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0704.0201

Weiqiang Wang

Ta Khongsap, Weiqiang Wang

Hecke-Clifford algebras and spin Hecke algebras I: the classical affine type

v3, proofs of Thms 3.4 and 3.11 modified and other minor changes, to appear in Transformation Groups

Transformation Groups, vol. 13 (2008), 389--412.

math.RT math.QA

Associated to the classical Weyl groups, we introduce the notion of degenerate spin affine Hecke algebras and affine Hecke-Clifford algebras. For these algebras, we establish the PBW properties, formulate the intertwiners, and describe the centers. We further develop connections of these algebras with the usual degenerate (i.e. graded) affine Hecke algebras of Lusztig by introducing a notion of degenerate covering affine Hecke algebras.

0704.0202

Simon Perdrix

Simon Perdrix

Towards Minimal Resources of Measurement-based Quantum Computation

8 pages

New J. Phys. 9 206 (2007)

10.1088/1367-2630/9/6/206

quant-ph

We improve the upper bound on the minimal resources required for measurement-based quantum computation. Minimizing the resources required for this model is a key issue for experimental realization of a quantum computer based on projective measurements. This new upper bound allows also to reply in the negative to the open question about the existence of a trade-off between observable and ancillary qubits in measurement-based quantum computation.

0704.0203

August Muench

August A. Muench, Charles J. Lada, K. L. Luhman, James Muzerolle and Erick Young

A Spitzer census of the IC 348 nebula

Accepted to AJ; 33 pages in emulateapj format.

Astron.J.134:411-444,2007

10.1086/518560

astro-ph

We present a Spitzer based census of the IC 348 nebula and embedded star cluster. Our Spitzer census supplemented by ground based spectra has added 42 class II T-Tauri sources to the cluster membership and identified ~20 class 0/I protostars. The population of IC 348 likely exceeds 400 sources after accounting statistically for unidentified diskless members. Our Spitzer census of IC 348 reveals a population of protostars that is anti-correlated spatially with the T-Tauri members, which comprise the centrally condensed cluster around a B star. The protostars are instead found mostly at the cluster periphery about 1 pc from the B star and spread out along a filamentary ridge. We find that the star formation rate in this protostellar ridge is consistent with that rate which built the exposed cluster while the presence of fifteen cold, starless, millimeter cores intermingled with this protostellar population indicates that the IC 348 nebula has yet to finish forming stars. We show that the IC 348 cluster is of order 3-5 crossing times old, and, as evidenced by its smooth radial profile and confirmed mass segregation, is likely relaxed. While it seems apparent that the current cluster configuration is the result of dynamical evolution and its primordial structure has been erased, our findings support a model where embedded clusters are built up from numerous smaller sub-clusters. Finally, the results of our Spitzer census indicate that the supposition that star formation must progress rapidly in a dark cloud should not preclude these observations that show it can be relatively long lived.

0704.0204

Marco Giuseppe Pala

Marco G. Pala, Michele Governale, J\"urgen K\"onig

Non-Equilibrium Josephson and Andreev Current through Interacting Quantum Dots

11 pages, 4 figures

New J. Phys. 9 (2007) 278

10.1088/1367-2630/9/8/278

cond-mat.supr-con cond-mat.mes-hall

We present a theory of transport through interacting quantum dots coupled to normal and superconducting leads in the limit of weak tunnel coupling. A Josephson current between two superconducting leads, carried by first-order tunnel processes, can be established by non-equilibrium proximity effect. Both Andreev and Josephson current is suppressed for bias voltages below a threshold set by the Coulomb charging energy. A $\pi$-transition of the supercurrent can be driven by tuning gate or bias voltages.

0704.0205

Paolo Esposito

P. Esposito, A. Tiengo, A. De Luca, F. Mattana

Discovery of X-ray emission from the young radio pulsar PSR J1357-6429

Revised version (minor changes in text and figures). Accepted for publication on Astronomy and Astrophysics Letters on 10/04/2007

Astronomy and Astrophysics, Volume 467, Issue 2, May IV 2007, pp.L45-L48

10.1051/0004-6361:20077480

astro-ph

We present the first X-ray detection of the very young pulsar PSR J1357-6429 (characteristic age of 7.3 kyr) using data from the XMM-Newton and Chandra satellites. We find that the spectrum is well described by a power-law plus blackbody model, with photon index Gamma=1.4 and blackbody temperature kT=160 eV. For the estimated distance of 2.5 kpc, this corresponds to a 2-10 keV luminosity of about 1.2E+32 erg/s, thus the fraction of the spin-down energy channeled by PSR J1357-6429 into X-ray emission is one of the lowest observed. The Chandra data confirm the positional coincidence with the radio pulsar and allow to set an upper limit of 3E+31 erg/s on the 2-10 keV luminosity of a compact pulsar wind nebula. We do not detect any pulsed emission from the source and determine an upper limit of 30% for the modulation amplitude of the X-ray emission at the radio frequency of the pulsar.

0704.0206

Stefano Lepri

Stefano Lepri, Giovanni Giacomelli

Resonant activation in bistable semiconductor lasers

Submitted to Phys. Rev. A

10.1103/PhysRevA.76.023815

physics.optics

We theoretically investigate the possibility of observing resonant activation in the hopping dynamics of two-mode semiconductor lasers. We present a series of simulations of a rate-equations model under random and periodic modulation of the bias current. In both cases, for an optimal choice of the modulation time-scale, the hopping times between the stable lasing modes attain a minimum. The simulation data are understood by means of an effective one-dimensional Langevin equation with multiplicative fluctuations. Our conclusions apply to both Edge Emitting and Vertical Cavity Lasers, thus opening the way to several experimental tests in such optical systems.

0704.0207

Madappa Prakash

M Prakash

Quark matter and the astrophysics of neutron stars

8 pages, 6 figures, Plenary talk in Quark Matter 2006 to appear in J. Phys. G: Nucl. Part. Phys. 34 (2007)

J.Phys.G34:S253-260,2007

10.1088/0954-3899/34/8/S10

astro-ph gr-qc nucl-th

Some of the means through which the possible presence of nearly deconfined quarks in neutron stars can be detected by astrophysical observations of neutron stars from their birth to old age are highlighted.

0704.0208

Seung-Moon Hong Mr

Tobias J. Hagge and Seung-Moon Hong

Some non-braided fusion categories of rank 3

18 pages, 7 figures, v2. Many expository improvements based on referee feedback, most notably to the proof of the main theorem and the section on pivotal structures. Fewer details are left to the reader. A new section outlines the structure of the proof of the main theorem and its relation to other results in the paper

math.GT math.QA

We classify all fusion categories for a given set of fusion rules with three simple object types. If a conjecture of Ostrik is true, our classification completes the classification of fusion categories with three simple object types. To facilitate the discussion we describe a convenient, concrete and useful variation of graphical calculus for fusion categories, discuss pivotality and sphericity in this framework, and give a short and elementary re-proof of the fact that the quadruple dual functor is naturally isomorphic to the identity.

0704.0209

Sangwook Park

Sangwook Park, David N. Burrows, Gordon P. Garmire (Penn State), Richard McCray (Colorado), Judith L. Racusin (Penn State), Svetozar A. Zhekov (Space Res Inst)

Chandra Observations of Supernova 1987A

8 pages, 4 figures (including 2 color figs), 3 tables. To appear in the proceedings of "Supernova 1987A: 20 Years after Supernovae and Gamma-Ray Bursters", held in Aspen CO. USA, Feb 19-23, 2007

AIP Conf.Proc.937:43-50,2007

10.1063/1.2803606

astro-ph

We have been monitoring Supernova (SN) 1987A with {\it Chandra X-Ray Observatory} since 1999. We present a review of previous results from our {\it Chandra} observations, and some preliminary results from new {\it Chandra} data obtained in 2006 and 2007. High resolution imaging and spectroscopic studies of SN 1987A with {\it Chandra} reveal that X-ray emission of SN 1987A originates from the hot gas heated by interaction of the blast wave with the ring-like dense circumstellar medium (CSM) that was produced by the massive progenitor's equatorial stellar winds before the SN explosion. The blast wave is now sweeping through dense CSM all around the inner ring, and thus SN 1987A is rapidly brightening in soft X-rays. At the age of 20 yr (as of 2007 January), X-ray luminosity of SN 1987A is $L_{\rm X}$ $\sim$ 2.4 $\times$ 10$^{36}$ ergs s$^{-1}$ in the 0.5$-$10 keV band. X-ray emission is described by two-component plane shock model with electron temperatures of $kT$ $\sim$ 0.3 and 2 keV. As the shock front interacts with dense CSM all around the inner ring, the X-ray remnant is now expanding at a much slower rate of $v$ $\sim$ 1400 km s$^{-1}$ than it was until 2004 ($v$ $\sim$ 6000 km s$^{-1}$).

0704.0210

Andrew Dancer

Andrew Dancer, Mckenzie Wang

Classification of superpotentials

10.1007/s00220-008-0641-z

math.DG

We extend our previous classification of superpotentials of ``scalar curvature type" for the cohomogeneity one Ricci-flat equations. We now consider the case not covered in our previous paper, i.e., when some weight vector of the superpotential lies outside (a scaled translate of) the convex hull of the weight vectors associated with the scalar curvature function of the principal orbit. In this situation we show that either the isotropy representation has at most 3 irreducible summands or the first order subsystem associated to the superpotential is of the same form as the Calabi-Yau condition for submersion type metrics on complex line bundles over a Fano K\"ahler-Einstein product.

0704.0211

Deryk Osthus

Daniela K\"uhn and Deryk Osthus

Linkedness and ordered cycles in digraphs

math.CO

The minimum semi-degree of a digraph D is the minimum of its minimum outdegree and its minimum indegree. We show that every sufficiently large digraph D with minimum semi-degree at least n/2 +k-1 is k-linked. The bound on the minimum semi-degree is best possible and confirms a conjecture of Manoussakis from 1990. We also determine the smallest minimum semi-degree which ensures that a sufficiently large digraph D is k-ordered, i.e. that for every ordered sequence of k distinct vertices of D there is a directed cycle which encounters these vertices in this order.

0704.0212

Krzysztof Turzynski

Z. Lalak, D. Langlois, S. Pokorski, K. Turzynski

Curvature and isocurvature perturbations in two-field inflation

29 pages, 12 figures; v2: updated references, discussion extended, matches the published version

JCAP 0707:014,2007

10.1088/1475-7516/2007/07/014

hep-th astro-ph gr-qc

We study cosmological perturbations in two-field inflation, allowing for non-standard kinetic terms. We calculate analytically the spectra of curvature and isocurvature modes at Hubble crossing, up to first order in the slow-roll parameters. We also compute numerically the evolution of the curvature and isocurvature modes from well within the Hubble radius until the end of inflation. We show explicitly for a few examples, including the recently proposed model of `roulette' inflation, how isocurvature perturbations affect significantly the curvature perturbation between Hubble crossing and the end of inflation.

0704.0213

Ketan Mulmuley D

Ketan D. Mulmuley Hariharan Narayanan

Geometric Complexity Theory V: On deciding nonvanishing of a generalized Littlewood-Richardson coefficient

This article has been withdrawn because it has been merged with the earlier article (GCT3) in the series, and a new article appears in this GCT5 slot now as shown in the abstract

cs.CC

This article has been withdrawn because it has been merged with the earlier article GCT3 (arXiv: CS/0501076 [cs.CC]) in the series. The merged article is now available as: Geometric Complexity Theory III: on deciding nonvanishing of a Littlewood-Richardson Coefficient, Journal of Algebraic Combinatorics, vol. 36, issue 1, 2012, pp. 103-110. (Authors: Ketan Mulmuley, Hari Narayanan and Milind Sohoni) The new article in this GCT5 slot in the series is: Geometric Complexity Theory V: Equivalence between blackbox derandomization of polynomial identity testing and derandomization of Noether's Normalization Lemma, in the Proceedings of FOCS 2012 (abstract), arXiv:1209.5993 [cs.CC] (full version) (Author: Ketan Mulmuley)

0704.0214

Miloslav Znojil

Miloslav Znojil

A schematic model of scattering in PT-symmetric Quantum Mechanics

16 pp., a part of the talk to be presented during the 2nd Int. Doppler-Institute Microconference on the Analytic and Algebraic Methods: Prague, Villa Lanna, April 3rd, 2007, cf. http://gemma.ujf.cas.cz/%7Eznojil/conf/micromeetingII.html

quant-ph hep-th

One-dimensional scattering problem admitting a complex, PT-symmetric short-range potential V(x) is considered. Using a Runge-Kutta-discretized version of Schroedinger equation we derive the formulae for the reflection and transmission coefficients and emphasize that the only innovation emerges in fact via a complexification of one of the potential-characterizing parameters.

0704.0215

Tomasz Rolski

Zbigniew Pucha{\l}a and Tomasz Rolski

The exact asymptotic of the collision time tail distribution for independent Brownian particles with different drifts

20 pages

Probab. Theor. Relat. Field., Vol. 142, No. 3-4, pp. 595-617, (2008)

10.1007/s00440-007-0116-8

math.PR

In this note we consider the time of the collision $\tau$ for $n$ independent Brownian motions $X^1_t,...,X_t^n$ with drifts $a_1,...,a_n$, each starting from $x=(x_1,...,x_n)$, where $x_1<...<x_n$. We show the exact asymptotics of $P_x(\tau>t) = C h(x)t^{-\alpha}e^{-\gamma t}(1 + o(1))$ as $t\to\infty$ and identify $C,h(x),\alpha,\gamma$ in terms of the drifts.

0704.0216

Alexander Mattausch

Alexander Mattausch and Oleg Pankratov

Ab initio Study of Graphene on SiC

4 pages, 3 figures, 1 table; Submitted to Physical Review Letters on 01/08/07

10.1103/PhysRevLett.99.076802

cond-mat.mtrl-sci

Employing density-functional calculations we study single and double graphene layers on Si- and C-terminated 1x1-6H-SiC surfaces. We show that, in contrast to earlier assumptions, the first carbon layer is covalently bonded to the substrate, and cannot be responsible for the graphene-type electronic spectrum observed experimentally. The characteristic spectrum of free-standing graphene appears with the second carbon layer, which exhibits a weak van der Waals bonding to the underlying structure. For Si-terminated substrate, the interface is metallic, whereas on C-face it is semiconducting or semimetallic for single or double graphene coverage, respectively.

0704.0217

Wiroonsak Santipach

Wiroonsak Santipach and Michael L. Honig

Capacity of a Multiple-Antenna Fading Channel with a Quantized Precoding Matrix

IEEE Trans. Inf. Theory, vol. 55, no. 3, pp. 1218--1234, March 2009

10.1109/TIT.2008.2011437

cs.IT math.IT

http://arxiv.org/licenses/nonexclusive-distrib/1.0/

Given a multiple-input multiple-output (MIMO) channel, feedback from the receiver can be used to specify a transmit precoding matrix, which selectively activates the strongest channel modes. Here we analyze the performance of Random Vector Quantization (RVQ), in which the precoding matrix is selected from a random codebook containing independent, isotropically distributed entries. We assume that channel elements are i.i.d. and known to the receiver, which relays the optimal (rate-maximizing) precoder codebook index to the transmitter using B bits. We first derive the large system capacity of beamforming (rank-one precoding matrix) as a function of B, where large system refers to the limit as B and the number of transmit and receive antennas all go to infinity with fixed ratios. With beamforming RVQ is asymptotically optimal, i.e., no other quantization scheme can achieve a larger asymptotic rate. The performance of RVQ is also compared with that of a simpler reduced-rank scalar quantization scheme in which the beamformer is constrained to lie in a random subspace. We subsequently consider a precoding matrix with arbitrary rank, and approximate the asymptotic RVQ performance with optimal and linear receivers (matched filter and Minimum Mean Squared Error (MMSE)). Numerical examples show that these approximations accurately predict the performance of finite-size systems of interest. Given a target spectral efficiency, numerical examples show that the amount of feedback required by the linear MMSE receiver is only slightly more than that required by the optimal receiver, whereas the matched filter can require significantly more feedback.

0704.0218

Yuri Pritykin

Yuri Pritykin

On Almost Periodicity Criteria for Morphic Sequences in Some Particular Cases

9 pages. To be presented on 11th International Conference on Developments in Language Theory (DLT'2007), Turku, Finland, July 2007.

cs.DM cs.LO

In some particular cases we give criteria for morphic sequences to be almost periodic (=uniformly recurrent). Namely, we deal with fixed points of non-erasing morphisms and with automatic sequences. In both cases a polynomial-time algorithm solving the problem is found. A result more or less supporting the conjecture of decidability of the general problem is given.

0704.0219

Joseph Gelfand

Joseph D. Gelfand, B. M. Gaensler, Patrick O. Slane, Daniel J. Patnaude, John P. Hughes, Fernando Camilo

The Radio Emission, X-ray Emission, and Hydrodynamics of G328.4+0.2: A Comprehensive Analysis of a Luminous Pulsar Wind Nebula, its Neutron Star, and the Progenitor Supernova Explosion

27 pages, 11 figures, accepted for publication in The Astrophysical Journal

Astrophys.J.663:468-486,2007

10.1086/518498

astro-ph

We present new observational results obtained for the Galactic non-thermal radio source G328.4+0.2 to determine both if this source is a pulsar wind nebula or supernova remnant, and in either case, the physical properties of this source. Using X-ray data obtained by XMM, we confirm that the X-ray emission from this source is heavily absorbed and has a spectrum best fit by a power law model of photon index=2 with no evidence for a thermal component, the X-ray emission from G328.4+0.2 comes from a region significantly smaller than the radio emission, and that the X-ray and radio emission are significantly offset from each other. We also present the results of a new high resolution (7 arcseconds) 1.4 GHz image of G328.4+0.2 obtained using the Australia Telescope Compact Array, and a deep search for radio pulsations using the Parkes Radio Telescope. We find that the radio emission has a flat spectrum, though some areas along the eastern edge of G328.4+0.2 have a steeper radio spectral index of ~-0.3. Additionally, we obtain a luminosity limit of the central pulsar of L_{1400} < 30 mJy kpc^2, assuming a distance of 17 kpc. In light of these observational results, we test if G328.4+0.2 is a pulsar wind nebula (PWN) or a large PWN inside a supernova remnant (SNR) using a simple hydrodynamic model for the evolution of a PWN inside a SNR. As a result of this analysis, we conclude that G328.4+0.2 is a young (< 10000 years old) pulsar wind nebula formed by a low magnetic field (<10^12 G) neutron star born spinning rapidly (<10 ms) expanding into an undetected SNR formed by an energetic (>10^51 ergs), low ejecta mass (M < 5 Solar Masses) supernova explosion which occurred in a low density (n~0.03 cm^{-3}) environment.

0704.0220

Jason Ulery

Jason Glyndwr Ulery (for the STAR Collaboration)

Three Particle Correlations from STAR

Talk given at IWCF 2006, Hangzhou, China. 8 Pages, 8 Figures

Int.J.Mod.Phys.E16:3123-3130,2008

10.1142/S0218301307009117

nucl-ex

Two-particle correlations have shown modification to the away-side shape in central Au+Au collisions relative to $pp$, d+Au and peripheral Au+Au collisions. Different scenarios can explain this modification including: large angle gluon radiation, jets deflected by transverse flow, path length dependent energy loss, Cerenkov gluon radiation of fast moving particles, and conical flow generated by hydrodynamic Mach-cone shock-waves. Three-particle correlations have the power to distinguish the scenarios with conical emission, conical flow and Cerenkov radiation, from other scenarios. In addition, the dependence of the observed shapes on the $p_T$ of the associated particles can be used to distinguish conical emission from a sonic boom (Mach-cone) and from QCD-Cerenkov radiation. We present results from STAR on 3-particle azimuthal correlations for a high $p_T$ trigger particle with two softer particles. Results are shown for $pp$, d+Au and high statistics Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV. An important aspect of the analysis is the subtraction of combinatorial backgrounds. Systematic uncertainties due to this subtraction and the flow harmonics v2 and v4 are investigated in detail. The implications of the results for the presence or absence of conical flow from Mach-cones are discussed.

0704.0221

Lawrence M. Krauss

Lawrence M. Krauss (1,2) and Robert J. Scherrer (2) ((1) Case Western Reserve University, (2) Vanderbilt University)

The Return of a Static Universe and the End of Cosmology

5th prize 2007 Gravity Research Foundation Essay Competition, to appear, GRG October 2007; typos corrected; references updated

Gen.Rel.Grav.39:1545-1550,2007; Int.J.Mod.Phys.D17:685-690,2008

10.1007/s10714-007-0472-9 10.1142/S0218271808012449

astro-ph gr-qc hep-ph hep-th

We demonstrate that as we extrapolate the current $\Lambda$CDM universe forward in time, all evidence of the Hubble expansion will disappear, so that observers in our "island universe" will be fundamentally incapable of determining the true nature of the universe, including the existence of the highly dominant vacuum energy, the existence of the CMB, and the primordial origin of light elements. With these pillars of the modern Big Bang gone, this epoch will mark the end of cosmology and the return of a static universe. In this sense, the coordinate system appropriate for future observers will perhaps fittingly resemble the static coordinate system in which the de Sitter universe was first presented.

0704.0222

Miguel \'Angel S\'anchez-Conde Mr.

Miguel A. Sanchez-Conde

Dark Matter annihilation in Draco: new considerations on the expected gamma flux

2 pages, 2 figures, to appear in the Proceedings of the First International GLAST Symposium, Stanford University, 5-8 February 2007

AIP Conf.Proc.921:510-511,2007

10.1063/1.2757426

astro-ph

A new estimation of the gamma-ray flux that we expect to detect from SUSY dark matter annihilation from the Draco dSph is presented using the DM density profiles compatible with the latest observations. This calculation takes also into account the important effect of the Point Spread Function (PSF) of the telescope. We show that this effect is crucial in the way we will observe and interpret a possible signal detection. Finally, we discuss the prospects to detect a possible gamma signal from Draco for MAGIC and GLAST.

0704.0223

Fu-Yan Bian

Yu-Qing Lou (1,2,3) and Wei-Gang Wang (1), ((1) Tsinghua Center For astrophysics, Tsinghua University, (2)The University of Chicago, (3) National Astronomical Observatories, Chinese Academy of Science.)

Magnetohydrodynamic Rebound Shocks of Supernovae

5 pages, 1 figure, Accepted for publication in MNRAS

Mon.Not.Roy.Astron.Soc.Lett.378:L54-L58,2007

10.1111/j.1745-3933.2007.00319.x

astro-ph

We construct magnetohydrodynamic (MHD) similarity rebound shocks joining `quasi-static' asymptotic solutions around the central degenerate core to explore an MHD model for the evolution of random magnetic field in supernova explosions. This provides a theoretical basis for further studying synchrotron diagnostics, MHD shock acceleration of cosmic rays, and the nature of intense magnetic field in compact objects. The magnetic field strength in space approaches a limiting ratio, that is comparable to the ratio of the ejecta mass driven out versus the progenitor mass, during this self-similar rebound MHD shock evolution. The intense magnetic field of the remnant compact star as compared to that of the progenitor star is mainly attributed to both the gravitational core collapse and the radial distribution of magnetic field.

0704.0224

Jason Ulery

Jason Glyndwr Ulery (for the STAR Collaboration)

Are There Mach Cones in Heavy Ion Collisions? Three-Particle Correlations from STAR

Poster shown at Quark Matter 2006, Shanghai, China. 6 Pages, 6 Figures

Int.J.Mod.Phys.E16:2005-2010,2007

10.1142/S0218301307007374

nucl-ex

We present results from STAR on 3-particle azimuthal correlations for a $3<p_T<4$ GeV/c trigger particle with two softer $1<p_T<2$ GeV/c particles. Results are shown for pp, d+Au and high statistics Au+Au collisions at $\sqrt{s_{NN}}=200 GeV$. We observe a 3-particle correlation in central Au+Au collisions which may indicate the presence of conical emission. In addition, the dependence of the observed signal angular position on the $p_T$ of the associated particles can be used to distinguish conical flow from simple QCD-\v{C}erenkov radiation. An important aspect of the analysis is the subtraction of combinatorial backgrounds. Systematic uncertainties due to this subtraction and the flow harmonics $v_2$ and $v_4$ are investigated in detail.

0704.0225

Alexander Kashlinsky

A. Kashlinsky and D. Band

Exploring First Stars Era with GLAST

to appear in Proceedings of 1st International GLAST Symposium

AIP Conf.Proc.921:243-245,2007

10.1063/1.2757312

astro-ph

Cosmic infrared background (CIB) includes emissions from objects inaccessible to current telescopic studies, such as the putative Population III, the first stars. Recently, strong direct evidence for significant CIB levels produced by the first stars came from CIB fluctuations discovered in deep Spitzer images. Such CIB levels should have left a unique absorption feature in the spectra of high-z GRBs and blazars as suggested in [4]. This is observable with GLAST sources at z>2 and measuring this absorption will give important information on energetics and constituents of the first stars era.

0704.0226

Francesco Tombesi

F. Tombesi (1,2), B. De Marco (3), K. Iwasawa (4), M. Cappi (1), M. Dadina (1), G. Ponti (1,2), G. Miniutti (5) and G.G.C. Palumbo (2) ((1) INAF-IASF Bologna, (2) UNIBO, (3) SISSA, (4) MPE, (5) Institute of Astronomy, Cambridge)

Correlated modulation between the redshifted Fe K alpha line and the continuum emission in NGC 3783

8 pages, 7 figures, to be published in Astronomy and Astrophysics

10.1051/0004-6361:20066713

astro-ph

It has been suggested that X-ray observations of rapidly variable Seyfert galaxies may hold the key to probe the gas orbital motions in the innermost regions of accretion discs around black holes and, thus, trace flow patterns under the effect of the hole strong gravitational field. We explore this possibility analizing XMM-Newton observations of the seyfert 1 galaxy NGC 3783. A detiled time-resolved spectral analysis is performed down to the shortest possible time-scales (few ks) using "excess maps" and cross-correlating light curves in different energy bands. In addition to a constant core of the Fe K alpha line, we detected a variable and redshifted Fe K alpha emission feature between 5.3-6.1 keV. The line exhibits a modulation on a time-scale of 27 ks that is similar to and in phase with a modulation of the 0.3-10 keV source continuum. The time-scale of the correlated variability of the redshifted Fe line and continuum agrees with the local dynamical time-scale of the accretion disc at 10 r_g around a black hole of 10^7 M_sun. Given the shape of the redshfted line emission and the overall X-ray variability pattern, the line is likely to arise from the relativistic region near the black hole.

0704.0227

Concettina Sfienti Dr

C.Sfienti, M. De Napoli, S. Bianchin, A.S. Botvina, J. Brzychczyk, A. Le Fevre, J. Lukasik, P. Pawlowski, W. Trautmann and the ALADiN2000 Collaboration

Isotopic Effects in Nuclear Reactions at Relativistic Energies

10 pages, 5 figures, Proceeding of the XLV International Winter Meeting on Nuclear Physics, Bormio (Italy), 14-21 January 2007

nucl-ex

A systematic study of isotopic effects in the break-up of projectile spectators at relativistic energies has been performed at the GSI laboratory with the ALADiN spectrometer coupled to the LAND neutron detector. Besides a primary beam of 124Sn, also secondary beams of 124La and 107Sn produced at the FRS fragment separator have been used in order to extend the range of isotopic compositions. The gross properties of projectile fragmentation are very similar for all the studied systems but specific isotopic effects have been observed in both neutron and charged particle production. The breakup temperatures obtained from the double ratios of isotopic yields have been extracted and compared with the limiting-temperature expectation.

0704.0228

Th. M. Nieuwenhuizen

Theo M. Nieuwenhuizen

Einstein vs Maxwell: Is gravitation a curvature of space, a field in flat space, or both?

5 pages, 1 figure

Europhys.Lett.78:10010,2007

10.1209/0295-5075/78/10010

gr-qc astro-ph quant-ph

Starting with a field theoretic approach in Minkowski space, the gravitational energy momentum tensor is derived from the Einstein equations in a straightforward manner. This allows to present them as {\it acceleration tensor} = const. $\times$ {\it total energy momentum tensor}. For flat space cosmology the gravitational energy is negative and cancels the material energy. In the relativistic theory of gravitation a bimetric coupling between the Riemann and Minkowski metrics breaks general coordinate invariance. The case of a positive cosmological constant is considered. A singularity free version of the Schwarzschild black hole is solved analytically. In the interior the components of the metric tensor quickly die out, but do not change sign, leaving the role of time as usual. For cosmology the $\Lambda$CDM model is covered, while there appears a form of inflation at early times. Here both the total energy and the zero point energy vanish.

0704.0229

Ketan Mulmuley D

Ketan D. Mulmuley

Geometric Complexity Theory VI: the flip via saturated and positive integer programming in representation theory and algebraic geometry

139 pages. Corrects error in the conjectural saturation hypothesis (SH) in the earlier version, which was pointed out in a recent paper of Briand et al (arXIv:0810.3163v1 [math.CO])

cs.CC

http://arxiv.org/licenses/nonexclusive-distrib/1.0/

This article belongs to a series on geometric complexity theory (GCT), an approach to the P vs. NP and related problems through algebraic geometry and representation theory. The basic principle behind this approach is called the flip. In essence, it reduces the negative hypothesis in complexity theory (the lower bound problems), such as the P vs. NP problem in characteristic zero, to the positive hypothesis in complexity theory (the upper bound problems): specifically, to showing that the problems of deciding nonvanishing of the fundamental structural constants in representation theory and algebraic geometry, such as the well known plethysm constants--or rather certain relaxed forms of these decision probelms--belong to the complexity class P. In this article, we suggest a plan for implementing the flip, i.e., for showing that these relaxed decision problems belong to P. This is based on the reduction of the preceding complexity-theoretic positive hypotheses to mathematical positivity hypotheses: specifically, to showing that there exist positive formulae--i.e. formulae with nonnegative coefficients--for the structural constants under consideration and certain functions associated with them. These turn out be intimately related to the similar positivity properties of the Kazhdan-Lusztig polynomials and the multiplicative structural constants of the canonical (global crystal) bases in the theory of Drinfeld-Jimbo quantum groups. The known proofs of these positivity properties depend on the Riemann hypothesis over finite fields and the related results. Thus the reduction here, in conjunction with the flip, in essence, says that the validity of the P vs. NP conjecture in characteristic zero is intimately linked to the Riemann hypothesis over finite fields and related problems.

0704.0230

Rene Duffard

R. Duffard and F. Roig

Two new basaltic asteroids in the Outer Main Belt?

13 pages, 3 figures, 2 tables

astro-ph

The identification of basaltic asteroids in the asteroid Main Belt and the description of their surface mineralogy is necessary to understand the diversity in the collection of basaltic meteorites. Basaltic asteroids can be identified from their visible reflectance spectra and are classified as V-type in the usual taxonomies. In this work, we report visible spectroscopic observations of two candidate V-type asteroids, (7472) Kumakiri and (10537) 1991 RY16, located in the outer Main Belt (a > 2.85 UA). These candidate have been previously identified by Roig and Gil-Hutton (2006, Icarus 183, 411) using the Sloan Digital Sky Survey colors. The spectroscopic observations have been obtained at the Calar Alto Observatory, Spain, during observational runs in November and December 2006. The spectra of these two asteroids show the steep slope shortwards of 0.70 microns and the deep absorption feature longwards of 0.75 microns that are characteristic of V-type asteroids. However, the presence of a shallow but conspicuous absorption band around 0.65 microns opens some questions about the actual mineralogy of these two asteroids. Such band has never been observed before in basaltic asteroids with the intensity we detected it. We discuss the possibility for this shallow absorption feature to be caused by the presence of chromium on the asteroid surface. Our results indicate that, together with (1459) Magnya, asteroids (7472) Kumakiri and (10537) 1991 RY16 may be the only traces of basaltic material found up to now in the outer Main Belt.

0704.0231

Joaquim Ortega-Cerda

Joaquim Ortega-Cerda

Interpolating and sampling sequences in finite Riemann surfaces

Bull. Lond. Math. Soc. 40 (2008), no. 5, 876--886

10.1112/blms/bdn071

math.CV

We provide a description of the interpolating and sampling sequences on a space of holomorphic functions with a uniform growth restriction defined on finite Riemann surfaces.

0704.0232

Christoph Bergbauer

Christoph Bergbauer, Dirk Kreimer

New algebraic aspects of perturbative and non-perturbative Quantum Field Theory

15 pages, Contribution to the Proceedings of the ICMP 2006, 2 typos corrected, final version

in "New Trends in Mathematical Physics; Selected contributions of the XVth International Congress on Mathematical Physics", V. Sidoravicius (Ed.), Springer (2009)

hep-th

http://arxiv.org/licenses/nonexclusive-distrib/1.0/

In this expository article we review recent advances in our understanding of the combinatorial and algebraic structure of perturbation theory in terms of Feynman graphs, and Dyson-Schwinger equations. Starting from Lie and Hopf algebras of Feynman graphs, perturbative renormalization is rephrased algebraically. The Hochschild cohomology of these Hopf algebras leads the way to Slavnov-Taylor identities and Dyson-Schwinger equations. We discuss recent progress in solving simple Dyson-Schwinger equations in the high energy sector using the algebraic machinery. Finally there is a short account on a relation to algebraic geometry and number theory: understanding Feynman integrals as periods of mixed (Tate) motives.

0704.0233

Sandro Wimberger

Andrea Tomadin, Riccardo Mannella, and Sandro Wimberger

Many-body interband tunneling as a witness for complex dynamics in the Bose-Hubbard model

4 pages, 3 figures

Phys. Rev. Lett. 98, 130402 (2007)

10.1103/PhysRevLett.98.130402

cond-mat.other

A perturbative model is studied for the tunneling of many-particle states from the ground band to the first excited energy band, mimicking Landau-Zener decay for ultracold, spinless atoms in quasi-one dimensional optical lattices subjected to a tunable tilting force. The distributions of the computed tunneling rates provide an independent and experimentally accessible signature of the regular-chaotic transition in the strongly correlated many-body dynamics of the ground band.

0704.0234

Gabriele Ghisellini

G. Ghirlanda (1), L. Nava (1,2), G. Ghisellini (1), C. Firmani (1,3) ((1) Osserv. Astr. di Brera, (2) Univ. degli Studi dell'Insubria, (3) U.N.A.M.)

Comments on ``Are Swift Gamma-Ray Bursts consistent with the Ghirlanda relation?", by Campana et al.(astro--ph/0703676)

3 pages

astro-ph

In their recent paper, Campana et al. (2007) found that 5 bursts, among those detected by Swift, are outliers with respect to the E_peak-E_gamma ("Ghirlanda") correlation. We instead argue that they are not.

0704.0235

Thomas G. Rizzo

Thomas G. Rizzo

The Determination of the Helicity of $W'$ Boson Couplings at the LHC

29 pages, 11 figures; discussion and reference added, typos corrected

JHEP 0705:037,2007

10.1088/1126-6708/2007/05/037

SLAC-PUB-12392

hep-ph hep-ex

Apart from its mass and width, the most important property of a new charged gauge boson, $W'$, is the helicity of its couplings to the SM fermions. Such particles are expected to exist in many extensions of the Standard Model. In this paper we explore the capability of the LHC to determine the $W'$ coupling helicity at low integrated luminosities in the $\ell +E_T^{miss}$ discovery channel. We find that measurements of the transverse mass distribution, reconstructed from this final state in the $W-W'$ interference region, provides the best determination of this quantity. To make such measurements requires integrated luminosities of $\sim 10(60) fb^{-1}$ assuming $M_{W'}=1.5(2.5)$ TeV and provided that the $W'$ couplings have Standard Model magnitude. This helicity determination can be further strengthened by the use of various discovery channel leptonic asymmetries, also measured in the same interference regime, but with higher integrated luminosities.

0704.0236

Claus Gerhardt

Claus Gerhardt

Curvature flows in semi-Riemannian manifolds

48 pages, v4: minor typos corrected, this version will be published

Geometric Flows (Huai-Dong Cao and Shing-Tung Yau, eds.), Surveys in Differential Geometry, vol. XII, International Press of Boston, Somerville, MA, 2008, pp. 113--165

math.DG

We prove that the limit hypersurfaces of converging curvature flows are stable, if the initial velocity has a weak sign, and give a survey of the existence and regularity results.

0704.0237

Christopher W. Mauche

Christopher W. Mauche, Duane A. Liedahl, Shizuka Akiyama (Lawrence Livermore Nat'l Lab.), Tomasz Plewa (University of Chicago)

Hydrodynamic and Spectral Simulations of HMXB Winds

4 pages including 2 color encapsulated postscript figures; LaTeX format, uses ptptex.cls; submitted for inclusion in the proceedings of "The Extreme Universe in the Suzaku Era" conference, to be published in Progress of Theoretical Physics, Supplement.

Prog.Theor.Phys.Suppl.169:196-199,2007

10.1143/PTPS.169.196

astro-ph

We describe preliminary results of a global model of the radiatively-driven photoionized wind and accretion flow of the high-mass X-ray binary Vela X-1. The full model combines FLASH hydrodynamic calculations, XSTAR photoionization calculations, HULLAC atomic data, and Monte Carlo radiation transport. We present maps of the density, temperature, velocity, and ionization parameter from a FLASH two-dimensional time-dependent simulation of Vela X-1, as well as maps of the emissivity distributions of the X-ray emission lines.

0704.0238

Geoffrey C. Bower

Geoffrey C. Bower (Berkeley), Alberto Bolatto (Berkeley), Eric Ford (CfA, Florida), Paul Kalas (Berkeley), Jim Ulvestad (NRAO)

Radio Astrometric Detection and Characterization of Extra-Solar Planets: A White Paper Submitted to the NSF ExoPlanet Task Force

astro-ph

The extraordinary astrometric accuracy of radio interferometry creates an important and unique opportunity for the discovery and characterization of exo-planets. Currently, the Very Long Baseline Array can routinely achieve better than 100 microarcsecond accuracy, and can approach 10 microarcsecond with careful calibration. We describe here RIPL, the Radio Interferometric PLanet search, a new program with the VLBA and the Green Bank 100 m telescope that will survey 29 low-mass, active stars over 3 years with sub-Jovian planet mass sensitivity at 1 AU. An upgrade of the VLBA bandwidth will increase astrometric accuracy by an order of magnitude. Ultimately, the colossal collecting area of the Square Kilometer Array could push astrometric accuracy to 1 microarcsecond, making detection and characterizaiton of Earth mass planets possible. RIPL and other future radio astrometric planet searches occupy a unique volume in planet discovery and characterization parameter space. The parameter space of astrometric searches gives greater sensitivity to planets at large radii than radial velocity searches. For the VLBA and the expanded VLBA, the targets of radio astrometric surveys are by necessity nearby, low-mass, active stars, which cannot be studied efficiently through the radial velocity method, coronagraphy, or optical interferometry. For the SKA, detection sensitivity will extend to solar-type stars. Planets discovered through radio astrometric methods will be suitable for characterization through extreme adaptive optics. The complementarity of radio astrometric techniques with other methods demonstrates that radio astrometry can play an important role in the roadmap for exoplanet discovery and characterization.

0704.0239

J. Dzubiella

Joachim Dzubiella

Interface dynamics of microscopic cavities in water

to appear in J. Chem. Phys

10.1063/1.2734962

cond-mat.soft

An analytical description of the interface motion of a collapsing nanometer-sized spherical cavity in water is presented by a modification of the Rayleigh-Plesset equation in conjunction with explicit solvent molecular dynamics simulations. Quantitative agreement is found between the two approaches for the time-dependent cavity radius $R(t)$ at different solvent conditions while in the continuum picture the solvent viscosity has to be corrected for curvature effects. The typical magnitude of the interface or collapse velocity is found to be given by the ratio of surface tension and fluid viscosity, $v\simeq\gamma/\eta$, while the curvature correction accelerates collapse dynamics on length scales below the equilibrium crossover scales ($\sim$1nm). The study offers a starting point for an efficient implicit modeling of water dynamics in aqueous nanoassembly and protein systems in nonequilibrium.

0704.0240

Dam Thanh Son

D. T. Son, A. O. Starinets

Viscosity, Black Holes, and Quantum Field Theory

23 pages, a review. New proof of the universality of the viscosity entropy ratio, new derivation of Kubo's formula; references added and minor typos corrected in version 2

Ann.Rev.Nucl.Part.Sci.57:95-118,2007

10.1146/annurev.nucl.57.090506.123120

INT PUB 07-02

hep-th

We review recent progress in applying the AdS/CFT correspondence to finite-temperature field theory. In particular, we show how the hydrodynamic behavior of field theory is reflected in the low-momentum limit of correlation functions computed through a real-time AdS/CFT prescription, which we formulate. We also show how the hydrodynamic modes in field theory correspond to the low-lying quasinormal modes of the AdS black p-brane metric. We provide a proof of the universality of the viscosity/entropy ratio within a class of theories with gravity duals and formulate a viscosity bound conjecture. Possible implications for real systems are mentioned.

0704.0241

Jim Hague

J.P.Hague

Superconducting states of the quasi-2D Holstein model: Effects of vertex and non-local corrections

Reprint to improve access. 14 pages. 10 figures.

J. Phys.: Condens. Matter vol. 17 (2005) 5663-5676

10.1088/0953-8984/17/37/005

cond-mat.supr-con

I investigate superconducting states in a quasi-2D Holstein model using the dynamical cluster approximation (DCA). The effects of spatial fluctuations (non-local corrections) are examined and approximations neglecting and incorporating lowest-order vertex corrections are computed. The approximation is expected to be valid for electron-phonon couplings of less than the bandwidth. The phase diagram and superconducting order parameter are calculated. Effects which can only be attributed to theories beyond Migdal--Eliashberg theory are present. In particular, the order parameter shows momentum dependence on the Fermi-surface with a modulated form and s-wave order is suppressed at half-filling. The results are discussed in relation to Hohenberg's theorem and the BCS approximation.

0704.0242

Vincent L. Fish

Vincent L. Fish (NRAO)

Masers and star formation

10 pages, iaus.cls, to appear in IAU Symp. 242 proceedings (Astrophysical masers and their environments)

10.1017/S1743921307012604

astro-ph

Recent observational and theoretical advances concerning astronomical masers in star forming regions are reviewed. Major masing species are considered individually and in combination. Key results are summarized with emphasis on present science and future prospects.

0704.0243

Johannes Bauer

J. Bauer and A.C. Hewson

Renormalized quasiparticles in antiferromagnetic states of the Hubbard model

15 pages, 17 figures; some minor changes and additional figure

Eur. Phys. J. B 57 (2007), 235.

10.1140/epjb/e2007-00175-6

cond-mat.str-el

We analyze the properties of the quasiparticle excitations of metallic antiferromagnetic states in a strongly correlated electron system. The study is based on dynamical mean field theory (DMFT) for the infinite dimensional Hubbard model with antiferromagnetic symmetry breaking. Self-consistent solutions of the DMFT equations are calculated using the numerical renormalization group (NRG). The low energy behavior in these results is then analyzed in terms of renormalized quasiparticles. The parameters for these quasiparticles are calculated directly from the NRG derived self-energy, and also from the low energy fixed point of the effective impurity. They are found to be in good agreement. We show that the main low energy features of the $\bf k$-resolved spectral density can be understood in terms of the quasiparticle picture. We also find that Luttinger's theorem is satisfied for the total electron number in the doped antiferromagnetic state.

0704.0244

Sangeeta Sharma

S. Sharma (1,2), S. Pittalis (2), S. Kurth (2), S. Shallcross (3), J. K. Dewhurst (4) and E. K. U. Gross (2)

Comparison of exact-exchange calculations for solids in current-spin-density- and spin-density-functional theory

4 pages, 1 fig, 2 tables

10.1103/PhysRevB.76.100401

cond-mat.mtrl-sci

The relative merits of current-spin-density- and spin-density-functional theory are investigated for solids treated within the exact-exchange-only approximation. Spin-orbit splittings and orbital magnetic moments are determined at zero external magnetic field. We find that for magnetic (Fe, Co and Ni) and non-magnetic (Si and Ge) solids, the exact-exchange current-spin-density functional approach does not significantly improve the accuracy of the corresponding spin-density functional results.

0704.0245

Konstantinos Zoubos

Andreas Brandhuber, Bill Spence, Gabriele Travaglini, Konstantinos Zoubos

One-loop MHV Rules and Pure Yang-Mills

40 pages. v2: Minor corrections, references added. Published version

JHEP0707:002,2007

10.1088/1126-6708/2007/07/002

QMUL-PH-07-09

hep-th hep-ph

It has been known for some time that the standard MHV diagram formulation of perturbative Yang-Mills theory is incomplete, as it misses rational terms in one-loop scattering amplitudes of pure Yang-Mills. We propose that certain Lorentz violating counterterms, when expressed in the field variables which give rise to standard MHV vertices, produce precisely these missing terms. These counterterms appear when Yang-Mills is treated with a regulator, introduced by Thorn and collaborators, which arises in worldsheet formulations of Yang-Mills theory in the lightcone gauge. As an illustration of our proposal, we show that a simple one-loop, two-point counterterm is the generating function for the infinite sequence of one-loop, all-plus helicity amplitudes in pure Yang-Mills, in complete agreement with known expressions.

0704.0246

Natalya A. Zimbovskaya

Natalya A. Zimbovskaya

Fermi-liquid effects in the transresistivity in quantum Hall double layers near $\nu= 1/2 $

5 pages, 2 figures

JETP 98,1231 (2004)

10.1134/1.1777636

cond-mat.mes-hall

Here, we present theoretical studies of the temperature and magnetic field dependences of the Coulomb drag transresistivity between two parallel layers of two dimensional electron gases in quantum Hall regime near half filling of the lowest Landau level. It is shown that Fermi-liquid interactions between the relevant quasiparticles could give a significant effect on the transresistivity, providing its independence of the interlayer spacing for spacings taking on values reported in the experiments. Obtained results agree with the experimental evidence.

0704.0247

Diederik Roest

S. L. Cacciatori, M. M. Caldarelli, D. Klemm, D. S. Mansi, D. Roest

Geometry of four-dimensional Killing spinors

70 pages, JHEP3. v2: new explicit solutions for G_0 = 0 and reference added

JHEP0707:046,2007

10.1088/1126-6708/2007/07/046

hep-th gr-qc

The supersymmetric solutions of N=2, D=4 minimal ungauged and gauged supergravity are classified according to the fraction of preserved supersymmetry using spinorial geometry techniques. Subject to a reasonable assumption in the 1/2-supersymmetric time-like case of the gauged theory, we derive the complete form of all supersymmetric solutions. This includes a number of new 1/4- and 1/2-supersymmetric possibilities, like gravitational waves on bubbles of nothing in AdS_4.

0704.0248

Ricardo Weder

Ricardo Weder

A Rigorous Time-Domain Analysis of Full--Wave Electromagnetic Cloaking (Invisibility)

The presentation of the results has been simplified. Comments and references have been added

physics.optics math-ph math.MP

There is currently a great deal of interest in the theoretical and practical possibility of cloaking objects from the observation by electromagnetic waves. The basic idea of these invisibility devices \cite{glu1, glu2, le},\cite{pss1} is to use anisotropic {\it transformation media} whose permittivity and permeability $\var^{\lambda\nu}, \mu^{\lambda\nu}$, are obtained from the ones, $\var_0^{\lambda\nu}, \mu^{\lambda\nu}_0$, of isotropic media, by singular transformations of coordinates. In this paper we study electromagnetic cloaking in the time-domain using the formalism of time-dependent scattering theory. This formalism allows us to settle in an unambiguous way the mathematical problems posed by the singularities of the inverse of the permittivity and the permeability of the {\it transformation media} on the boundary of the cloaked objects. We write Maxwell's equations in Schr\"odinger form with the electromagnetic propagator playing the role of the Hamiltonian. We prove that the electromagnetic propagator outside of the cloaked objects is essentially self-adjoint. Moreover, the unique self-adjoint extension is unitarily equivalent to the electromagnetic propagator in the medium $\var_0^{\lambda\nu}, \mu^{\lambda\nu}_0$. Using this fact, and since the coordinate transformation is the identity outside of a ball, we prove that the scattering operator is the identity. Our results give a rigorous proof that the construction of \cite{glu1, glu2, le}, \cite{pss1} perfectly cloaks passive and active devices from observation by electromagnetic waves. Furthermore, we prove cloaking for general anisotropic materials. In particular, our results prove that it is possible to cloak objects inside general crystals.

0704.0249

Michael Potthoff

Jutta Ortloff, Matthias Balzer, Michael Potthoff

Non-perturbative conserving approximations and Luttinger's sum rule

13 pages, 10 figures, revised version with slightly extended discussion, accepted by EPJB

10.1140/epjb/e2007-00203-7

cond-mat.str-el

Weak-coupling conserving approximations can be constructed by truncations of the Luttinger-Ward functional and are well known as thermodynamically consistent approaches which respect macroscopic conservation laws as well as certain sum rules at zero temperature. These properties can also be shown for variational approximations that are generated within the framework of the self-energy-functional theory without a truncation of the diagram series. Luttinger's sum rule represents an exception. We analyze the conditions under which the sum rule holds within a non-perturbative conserving approximation. Numerical examples are given for a simple but non-trivial dynamical two-site approximation. The validity of the sum rule for finite Hubbard clusters and the consequences for cluster extensions of the dynamical mean-field theory are discussed.

0704.0250

Vladimir Dobrosavljevic

S. Pankov and V. Dobrosavljevic

2D-MIT as self-doping of a Wigner-Mott insulator

Contribution to the Proceedings of SCES2007; 2 pages, 1 figure.

Physica B 403, 1440 (2008)

10.1016/j.physb.2007.10.365

cond-mat.str-el cond-mat.dis-nn

We consider an interaction-driven scenario for the two-dimensional metal-insulator transition in zero magnetic field (2D-MIT), based on melting the Wigner crystal through vacancy-interstitial pair formation. We show that the transition from the Wigner-Mott insulator to a heavy Fermi liquid emerges as an instability to self-doping, resembling conceptually the solid to normal liquid transition in He3. The resulting physical picture naturally explains many puzzling features of the 2D-MIT.

0704.0251

Gilad Gour

Gilad Gour, Nolan R. Wallach

Entanglement of Subspaces and Error Correcting Codes

8 pages, Published Version

Phys. Rev. A 76, 042309 (2007)

10.1103/PhysRevA.76.042309

quant-ph

We introduce the notion of entanglement of subspaces as a measure that quantify the entanglement of bipartite states in a randomly selected subspace. We discuss its properties and in particular we show that for maximally entangled subspaces it is additive. Furthermore, we show that maximally entangled subspaces can play an important role in the study of quantum error correction codes. We discuss both degenerate and non-degenerate codes and show that the subspace spanned by the logical codewords of a non-degenerate code is a 2k-totally (maximally) entangled subspace. As for non-degenerate codes, we provide a mathematical definition in terms of subspaces and, as an example, we analyze Shor's nine qubits code in terms of 22 mutually orthogonal subspaces.

0704.0252

Ashutosh Alok

Ashutosh Kumar Alok and S. Uma Sankar

Does the present data on B_s - bar B_s mixing rule out a large enhancement in the branching ratio of B_s --> mu+ mu- ?

7 pages, no figures

hep-ph

In this letter, we consider the constraints imposed by the recent measurement of B_s - bar B_s mixing on the new physics contribution to the rare decay B_s --> mu+ mu-. New physics in the form vector and axial-vector couplings is already severely constrained by the data on B --> (K,K*) mu+ mu-. Here, we show that B_s - bar B_s mixing data, together with the data on K0 - bar K0 mixing and K_L --> mu+ mu- decay rate, strongly constrain the scalar-pseudoscalar contribution to B_s --> mu+ mu-. We conclude that new physics can at best lead to a factor of 2 increase in the branching ratio of B_s --> mu+ mu- compared to its Standard Model expectation.

0704.0253

Paul Harvey

Paul M. Harvey, Luisa M. Rebull, Tim Brooke, William J. Spiesman, Nicholas Chapman, Tracy L. Huard, Neal J. Evans II, Lucas Cieza, Shih-Ping Lai, Lori E. Allen, Lee G. Mundy, Deborah L. Padgett, Anneila I. Sargent, Karl R. Stapelfeldt, Philip C. Myers, Ewine F. van Dishoeck, Geoffrey A. Blake, David W. Koerner

The Spitzer c2d Survey of Large, Nearby, Interstellar Clouds VIII. Serpens Observed with MIPS

Astrophys.J.663:1139-1148,2007

10.1086/518647

astro-ph

We present maps of 1.5 square degrees of the Serpens dark cloud at 24, 70, and 160\micron observed with the Spitzer Space Telescope MIPS Camera. More than 2400 compact sources have been extracted at 24um, nearly 100 at 70um, and 4 at 160um. We estimate completeness limits for our 24um survey from Monte Carlo tests with artificial sources inserted into the Spitzer maps. We compare source counts, colors, and magnitudes in the Serpens cloud to two reference data sets, a 0.50 deg^2 set on a low-extinction region near the dark cloud, and a 5.3 deg^2 subset of the SWIRE ELAIS N1 data that was processed through our pipeline. These results show that there is an easily identifiable population of young stellar object candidates in the Serpens Cloud that is not present in either of the reference data sets. We also show a comparison of visual extinction and cool dust emission illustrating a close correlation between the two, and find that the most embedded YSO candidates are located in the areas of highest visual extinction.

0704.0254

Alexandre Alves

Alexandre Alves and Oscar Eboli

Unravelling the sbottom spin at the CERN LHC

9 pages, 11 figures

Phys.Rev.D75:115013,2007

10.1103/PhysRevD.75.115013

hep-ph

Establishing that a signal of new physics is undoubtly supersymmetric requires not only the discovery of the supersymmetric partners but also probing their spins and couplings. We show that the sbottom spin can be probed at the CERN Large Hadron Collider using only angular correlations in sbottom pair production with subsequent decay of sbottoms into bottom quark plus the lightest neutralino, which allow us to distinguish a universal extra dimensional interpretation with a fermionic heavy bottom quark from supersymmetry with a bosonic bottom squark. We demonstrate that this channel provides a clear indication of the sbottom spin provided the sbottom production rate and branching ratio into bottom quark plus the lightest neutralino are sufficiently large to have a clear signal above Standard Model backgrounds.

0704.0255

Felipe Marin

Felipe Marin (Chicago, KICP), Risa Wechsler (KIPAC, Stanford), Joshua Frieman (Chicago, KICP and Fermilab), Robert Nichol (ICG, Portsmouth)

Modeling the three-point correlation function

12 pages, 11 figures, ApJ accepted. Corrected typos, minor changes from referee comments

Astrophys.J.672:849-860,2008

10.1086/523628

astro-ph

We present new predictions for the galaxy three-point correlation function (3PCF) using high-resolution dissipationless cosmological simulations of a flat LCDM Universe which resolve galaxy-size halos and subhalos. We create realistic mock galaxy catalogs by assigning luminosities and colors to dark matter halos and subhalos, and we measure the reduced 3PCF as a function of luminosity and color in both real and redshift space. As galaxy luminosity and color are varied, we find small differences in the amplitude and shape dependence of the reduced 3PCF, at a level qualitatively consistent with recent measurements from the SDSS and 2dFGRS. We confirm that discrepancies between previous 3PCF measurements can be explained in part by differences in binning choices. We explore the degree to which a simple local bias model can fit the simulated 3PCF. The agreement between the model predictions and galaxy 3PCF measurements lends further credence to the straightforward association of galaxies with CDM halos and subhalos.

0704.0256

Paul Harvey

Paul M. Harvey and Andrew Oldag

Multi-spectral Observations of Lunar Occultations: I. Resolving The Dust Shell Around AFGL 5440

Astrophys.J.663:543-552,2007

10.1086/518588

astro-ph

We present observations and modeling of a lunar occultation of the dust-enshrouded carbon star AFGL 5440. The observations were made over a continuous range of wavelengths from 1 - 4um with a high-speed spectrophotometer designed expressly for this purpose. We find that the occultation fringes cannot be fit by any single-size model. We use the DUSTY radiative transfer code to model a circumstellar shell and fit both the observed occultation light curves and the spectral energy distribution described in the literature. We find a strong constraint on the inner radius of the dust shell, Tmax = 950 K +/- 50K, and optical depth at 5um of 0.5 +/- 0.1. The observations are best fit by models with a density gradient of r^-2 or the gradient derived by Ivezic & Elitzur for a radiatively driven hydrodynamic outflow. Our models cannot fit the observed IRAS 60um flux without assuming a substantial abundance of graphite or by assuming a substantially higher mass-loss rate in the past.

0704.0257

Tara S. Holm

Tara S. Holm

Orbifold cohomology of abelian symplectic reductions and the case of weighted projective spaces

20 pages, 3 figures, 3 tables

math.SG math.AG

These notes accompany a lecture about the topology of symplectic (and other) quotients. The aim is two-fold: first to advertise the ease of computation in the symplectic category; and second to give an account of some new computations for weighted projective spaces. We start with a brief exposition of how orbifolds arise in the symplectic category, and discuss the techniques used to understand their topology. We then show how these results can be used to compute the Chen-Ruan orbifold cohomology ring of abelian symplectic reductions. We conclude by comparing the several rings associated to a weighted projective space. We make these computations directly, avoiding any mention of a stacky fan or of a labeled moment polytope.

0704.0258

Wschebor Nicolas

Diego Guerra, Ramon Mendez-Galain and Nicolas Wschebor

Correlation functions in the Non Perturbative Renormalization Group and field expansion

20 pages, 6 figures. Minor changes. Version to be published in EPJ B

Eur.Phys.J.B59:357-365,2007

10.1140/epjb/e2007-00296-x

hep-th cond-mat.stat-mech

The usual procedure of including a finite number of vertices in Non Perturbative Renormalization Group equations in order to obtain $n$-point correlation functions at finite momenta is analyzed. This is done by exploiting a general method recently introduced which includes simultaneously all vertices although approximating their momentum dependence. The study is performed using the self-energy of the tridimensional scalar model at criticality. At least in this example, low order truncations miss quantities as the critical exponent $\eta$ by as much as 60%. However, if one goes to high order truncations the procedure seems to converge rapidly.

0704.0259

Scott J. Kenyon

Scott J. Kenyon, Benjamin C. Bromley, David P. O'Brien, Donald R. Davis

Formation and Collisional Evolution of Kuiper Belt Objects

23 pages, 9 figures, 1 table; to appear in `Transneptunian Objects', Barucci et al. eds., University of Arizona Press

astro-ph

This chapter summarizes analytic theory and numerical calculations for the formation and collisional evolution of KBOs at 20--150 AU. We describe the main predictions of a baseline self-stirring model and show how dynamical perturbations from a stellar flyby or stirring by a giant planet modify the evolution. Although robust comparisons between observations and theory require better KBO statistics and more comprehensive calculations, the data are broadly consistent with KBO formation in a massive disk followed by substantial collisional grinding and dynamical ejection. However, there are important problems reconciling the results of coagulation and dynamical calculations. Contrasting our current understanding of the evolution of KBOs and asteroids suggests that additional observational constraints, such as the identification of more dynamical families of KBOs (like the 2003 EL61 family), would provide additional information on the relative roles of collisional grinding and dynamical ejection in the Kuiper Belt. The uncertainties also motivate calculations that combine collisional and dynamical evolution, a `unified' calculation that should give us a better picture of KBO formation and evolution.

0704.0260

Sergiy Torba M.

M. L. Gorbachuk, S. M. Torba

On Existence of Boundary Values of Polyharmonic Functions

10 pages

Methods Funct. Anal. Topol. 10, No.2, 4-12 (2004)

math.FA math.AP

In trigonometric series terms all polyharmonic functions inside the unit disk are described. For such functions it is proved the existence of their boundary values on the unit circle in the space of hyperfunctions. The necessary and sufficient conditions are presented for the boundary value to belong to certain subspaces of the space of hyperfunctions.

0704.0261

Scott Randall

Scott W. Randall, Maxim Markevitch, Douglas Clowe, Anthony H. Gonzalez, and Marusa Bradac

Constraints on the Self-Interaction Cross-Section of Dark Matter from Numerical Simulations of the Merging Galaxy Cluster 1E 0657-5

10.1086/587859

astro-ph

(Abridged) We compare recent results from X-ray, strong lensing, weak lensing, and optical observations with numerical simulations of the merging galaxy cluster 1E0657-56. X-ray observations reveal a bullet-like subcluster with a prominent bow shock, while lensing results show that the positions of the total mass peaks are consistent with the centroids of the collisionless galaxies (and inconsistent with the X-ray brightness peaks). Previous studies, based on older observational datasets, have placed upper limits on the self-interaction cross-section of dark matter per unit mass, sigma/m, using simplified analytic techniques. In this work, we take advantage of new, higher-quality observational datasets by running N-body simulations of 1E0657-56 that include the effects of self-interacting dark matter, and comparing the results with observations. Furthermore, the recent data allow for a new independent method of constraining sigma/m, based on the non-observation of an offset between the bullet subcluster mass peak and galaxy centroid. This new method places an upper limit (68% confidence) of sigma/m < 1.25 cm^2/g. If we make the assumption that the subcluster and the main cluster had equal mass-to-light ratios prior to the merger, we derive our most stringent constraint of sigma/m < 0.7 cm^2/g, which comes from the consistency of the subcluster's observed mass-to-light ratio with the main cluster's, and with the universal cluster value, ruling out the possibility of a large fraction of dark matter particles being scattered away due to collisions. Our limit is a slight improvement over the previous result from analytic estimates, and rules out most of the 0.5 - 5cm^2/g range invoked to explain inconsistencies between the standard collisionless cold dark matter model and observations.

0704.0262

Matteo Bertolini

Riccardo Argurio, Matteo Bertolini, Gabriele Ferretti, Alberto Lerda and Christoffer Petersson

Stringy Instantons at Orbifold Singularities

Latex, 29 pages, 6 figures. v3: typos corrected, one comment and refs added, published version

JHEP 0706:067,2007

10.1088/1126-6708/2007/06/067

hep-th

We study the effects produced by D-brane instantons on the holomorphic quantities of a D-brane gauge theory at an orbifold singularity. These effects are not limited to reproducing the well known contributions of the gauge theory instantons but also generate extra terms in the superpotential or the prepotential. On these brane instantons there are some neutral fermionic zero-modes in addition to the ones expected from broken supertranslations. They are crucial in correctly reproducing effects which are dual to gauge theory instantons, but they may make some other interesting contributions vanish. We analyze how orientifold projections can remove these zero-modes and thus allow for new superpotential terms. These terms contribute to the dynamics of the effective gauge theory, for instance in the stabilization of runaway directions.

0704.0263

Gregory Eyink L

Gregory L. Eyink

Turbulent Diffusion of Lines and Circulations

13 pages; no figures

10.1016/j.physleta.2007.04.054

physics.flu-dyn physics.plasm-ph

We study material lines and passive vectors in a model of turbulent flow at infinite-Reynolds number, the Kraichnan-Kazantsev ensemble of velocities that are white-noise in time and rough (Hoelder continuous) in space. It is argued that the phenomenon of ``spontaneous stochasticity'' generalizes to material lines and that conservation of circulations generalizes to a ``martingale property'' of the stochastic process of lines.

0704.0264

Jian Dai

Jian Dai

Gluon Radiation of an Expanding Color Skyrmion in the Quark-Gluon Plasma

8 pages, 3 eps figures

hep-ph hep-th nucl-th

The density of states and energy spectrum of the gluon radiation are calculated for the color current of an expanding hydrodynamic skyrmion in the quark gluon plasma with a semiclassical method. Results are compared with those in literatures.

0704.0265

Stefano Covino

A. Dolcini, F. Farfanelli, S. Ciprini, A. Treves, S. Covino, G. Tosti, E. Pian, B. Sbarufatti, E. Molinari, G. Chincarini, F.M. Zerbi, G. Malaspina, P. Conconi, L. Nicastro, E. Palazzi, V. Testa, F. Vitali, L.A. Antonelli, J. Danziger, G. Tagliaferri, E. Meurs, S. Vergani, A. Fernandez-Soto, E. Distefano, G. Cutispoto, F. D'Alessio

REM near-IR and optical multiband observations of PKS2155-304 in 2005

This paper is the corrected version of the paper published in A&A 469 503. It contains the material in the "Errata Corrrige", in press in A&A

Astron.Astrophys.469:503,2007

10.1051/0004-6361:20066477

astro-ph

Spectral variability is the main tool for constraining emission models of BL Lac objects. By means of systematic observations of the BL Lac prototype PKS 2155-304 in the infrared-optical band, we explore variability on the scales of months, days and hours. We made our observations with the robotic 60 cm telescope REM located at La Silla, Chile. VRIJHK filters were used. PKS 2155-304 was observed from May to December 2005. The wavelength interval explored, the total number of photometric points and the short integration time render our photometry substantially superior to previous ones for this source. On the basis of the intensity and colour we distinguish three different states of the source, each of duration of months, which include all those described in the literature. In particular, we report the highest state ever detected in the H band. The source varied by a factor of 4 in this band, much more than in the V band (a factor ~2). The source softened with increasing intensity, contrary to the general pattern observed in the UV-X-ray bands. On five nights of November we had nearly continuous monitoring for 2-3 hours. A variability episode with a time scale of ~24 h is well documented, a much more rapid flare with t=1-2 h, is also apparent, but is supported by relatively few points.

0704.0266

Jennifer L. Hoffman

Jennifer L. Hoffman

Supernova Polarization and the Type IIn Classification

5 pages, 4 figures; to appear in "Supernova 1987A: 20 Years After: Supernovae and Gamma-Ray Bursters", AIP, New York, eds. S. Immler, K.W. Weiler, and R. McCray. v2: References added, typos corrected, and figures slightly modified for legibility when reduced in size

AIP Conf.Proc.937:365-369,2007

10.1063/1.2803592

astro-ph

While the members of the Type IIn category of supernovae are united by the presence of strong multicomponent Balmer emission lines in their spectra, they are quite heterogeneous with respect to other properties such as Balmer line profiles, light curves, strength of radio emission, and intrinsic brightness. We are now beginning to see variety among SNe IIn in their polarimetric characteristics as well, some but not all of which may be due to inclination angle effects. The increasing number of known "hybrid" SNe with IIn-like emission lines suggests that circumstellar material may be more common around all types of SNe than previously thought. Investigation of the correlations between spectropolarimetric signatures and other IIn attributes will help us address the question of classification of "interacting SNe" and the possibility of distinguishing different groups within the diverse IIn subclass.

0704.0267

Cynthia S. Froning

C.S. Froning, E.L. Robinson, and M.A. Bitner

Near-Infrared Spectra of the Black Hole X-Ray Binary, A0620-00

Accepted for publication in the Astrophysical Journal

Astrophys.J.663:1215-1224,2007

10.1086/518820

astro-ph

We present broadband NIR spectra of A0620-00 obtained with SpeX on the IRTF. The spectrum is characterized by a blue continuum on which are superimposed broad emission lines of HI and HeII and a host of narrower absorption lines of neutral metals and molecules. Spectral type standard star spectra scaled to the dereddened spectrum of A0620-00 in K exceed the A0620-00 spectrum in J and H for all stars of spectral type K7V or earlier, demonstrating that the donor star, unless later than K7V, cannot be the sole NIR flux source in A0620-00. In addition, the atomic absorption lines in the K3V spectrum are too weak with respect to those of A0620-00 even at 100% donor star contribution, restricting the spectral type of the donor star in A0620-00 to later than K3V. Comparison of the A0620-00 spectrum to scaled K star spectra indicates that the CO absorption features are significantly weaker in A0620-00 than in field dwarf stars. Fits of scaled model spectra of a Roche lobe-filling donor star to the spectrum of A0620-00 show that the best match to the CO absorption lines is obtained when the C abundance is reduced to [C/H] = -1.5. The donor star contribution in the H waveband is determined to be 82+-2%. Combined with previous published results from Froning & Robinson (2001) and Marsh et al. (1994), this gives a precise mass for the black hole in A0620-00 of M_BH = 9.7+-0.6 M_solar.

0704.0268

Mark Whitney

Mark Whitney, Nemanja Isailovic, Yatish Patel, John Kubiatowicz

Automated Generation of Layout and Control for Quantum Circuits

16 pages, 11 figures, To appear in ACM Computing Frontiers 2007, this version contains expanded related work

quant-ph

We present a computer-aided design flow for quantum circuits, complete with automatic layout and control logic extraction. To motivate automated layout for quantum circuits, we investigate grid-based layouts and show a performance variance of four times as we vary grid structure and initial qubit placement. We then propose two polynomial-time design heuristics: a greedy algorithm suitable for small, congestion-free quantum circuits and a dataflow-based analysis approach to placement and routing with implicit initial placement of qubits. Finally, we show that our dataflow-based heuristic generates better layouts than the state-of-the-art automated grid-based layout and scheduling mechanism in terms of latency and potential pipelinability, but at the cost of some area.

0704.0269

Manasvita Joshi

M. Joshi and M. Boettcher

Modeling the Spectral Energy Distribution and Variability of 3C 66A during the WEBT campaign of 2003 -- 2004

23 pages, 9 figures, submitted to and accepted for publication in ApJ

Astrophys.J.662:884-891,2007

10.1086/518210

astro-ph

The BL Lac object 3C 66A was observed in an extensive multiwavelength monitoring campaign from July 2003 till April 2004. The spectral energy distribution (SED) was measured over the entire electromagnetic spectrum, with flux measurements from radio to X-ray frequencies and upper limits in the very high energy (VHE) gamma-ray regime. Here, we use a time-dependent leptonic jet model to reproduce the SED and optical spectral variability observed during our multiwavelength campaign. Our model simulations could successfully reproduce the observed SED and optical light curves and predict an intrinsic cutoff value for the VHE gamma-ray emission at ~ 4 GeV. The effect of the optical depth due to the intergalactic infrared background radiation (IIBR) on the peak of the high-energy component of 3C 66A was found to be negligible. Also, the presence of a broad line region (BLR) in the case of 3C 66A may play an important role in the emission of gamma-ray photons when the emission region is very close to the central engine, but further out, the production mechanism of hard X-ray and gamma-ray photons becomes rapidly dominated by synchrotron self-Compton emission. We further discuss the possibility of an observable X-ray spectral variability pattern. The simulated results do not predict observable hysteresis patterns in the optical or soft X-ray regimes for major flares on multi-day time scales.

0704.0270

Xavier Bonfils

X. Bonfils, M. Mayor, X. Delfosse, T. Forveille, M. Gillon, C. Perrier, S. Udry, F. Bouchy, C. Lovis, F. Pepe, D. Queloz, N. C. Santos and J.-L. Bertaux

The HARPS search for southern extra-solar planets. X. A m sin i = 11 Mearth planet around the nearby spotted M dwarf GJ 674

submitted to A&A (January 09, 2007)

10.1051/0004-6361:20077068

astro-ph

Context: How planet properties depend on stellar mass is a key diagnostic of planetary formation mechanisms. Aims: This motivates planet searches around stars which are significantly more massive or less massive than the Sun, and in particular our radial velocity search for planets around very-low mass stars. Methods: As part of that program, we obtained measurements of GJ 674, an M2.5 dwarf at d=4.5 pc, which have a dispersion much in excess of their internal errors. An intensive observing campaign demonstrates that the excess dispersion is due to two superimposed coherent signals, with periods of 4.69 and 35 days. Results: These data are well described by a 2-planet Keplerian model where each planet has a ~11 Mearth minimum mass. A careful analysis of the (low level) magnetic activity of GJ 674 however demonstrates that the 35-day period coincides with the stellar rotation period. This signal therefore originates in a spot inhomogeneity modulated by stellar rotation. The 4.69-day signal on the other hand is caused by a bona-fide planet, GJ 674b. Conclusion: Its detection adds to the growing number of Neptune-mass planets around M-dwarfs, and reinforces the emerging conclusion that this mass domain is much more populated than the jovian mass range. We discuss the metallicity distributions of M dwarf with and without planets and find a low 11% probability that they are drawn from the same parent distribution. Moreover, we find tentative evidence that the host star metallicity correlates with the total mass of their planetary system.

0704.0271

Edgardo Brigatti

E. Brigatti, V. Schwammle and Minos A. Neto

An individual based model with global competition interaction: fluctuations effects in pattern formation

9 pages, 9 figures, minor changes

Physical Review E 77, 021914 (2008)

10.1103/PhysRevE.77.021914

cond-mat.stat-mech q-bio.PE

We present some numerical results obtained from a simple individual based model that describes clustering of organisms caused by competition. Our aim is to show how, even when a deterministic description developed for continuum models predicts no pattern formation, an individual based model displays well defined patterns, as a consequence of fluctuations effects caused by the discrete nature of the interacting agents.

0704.0272

Monica Ivette Rodriguez

Monica Ivette Rodriguez, Tommy Wiklind, Ronald J. Allen, Vladimir Escalante, and Laurent Loinard

A Comparison between Anomalous 6-cm H$_2$CO Absorption and CO(1-0) Emission in the L1204/S140

9 pages 6 figures ApJ:accepted

Astrophys.J.663:824-833,2007

10.1086/518553

astro-ph

We report observations of the dust cloud L1204 with the Onsala 25-m telescope in the 6 cm (1$_{11}-1_{10}$) transition of \htco. The observed region includes the S140 H${\alpha}$ arc. This spectral line is seen here in absorption against the cosmic microwave background, indicating the presence of widespread warm molecular gas at intermediate densities. Overall, the distributions of H$_2$CO and CO (taken from the literature) are fairly similar, though significant differences exist at small scales. Most notably, while the CO peak is nearly coincident with the S140 H${\alpha}$ arc, the maximum H$_2$CO absorption is clearly separated from it by a full 10$'$ beam ($\sim$ 3 pc). We argue that these differences result from differing abundances and excitation requirements. The CO(1-0) line is more optically thick and more biased towards warm gas than the H$_2$CO 6 cm line. On the other hand, formaldehyde is more easily photodissociated and is, therefore, a poorer tracer of the molecular gas located immediately behind Photon Dominated Regions.

0704.0273

David Cimasoni

David Cimasoni, Nicolai Reshetikhin

Dimers on surface graphs and spin structures. II

23 pages, 3 figures

Comm. Math. Phys. 281 (2008), 445-468

10.1007/s00220-008-0488-3

math-ph math.GT math.MP

In a previous paper, we showed how certain orientations of the edges of a graph G embedded in a closed oriented surface S can be understood as discrete spin structures on S. We then used this correspondence to give a geometric proof of the Pfaffian formula for the partition function of the dimer model on G. In the present article, we generalize these results to the case of compact oriented surfaces with boundary. We also show how the operations of cutting and gluing act on discrete spin structures and how they change the partition function. These operations allow to reformulate the dimer model as a quantum field theory on surface graphs.

0704.0274

Georg von Hippel

Georg M. von Hippel

New version announcement for TaylUR, an arbitrary-order diagonal automatic differentiation package for Fortran 95

3 pages, uses elsart.cls

Comput.Phys.Commun. 176 (2007) 710-711

10.1016/j.cpc.2007.03.008

physics.comp-ph

We present a new version of TaylUR, a Fortran 95 module to automatically compute the numerical values of a complex-valued function's derivatives with respect to several variables up to an arbitrary order in each variable, but excluding mixed derivatives. The new version fixes a potentially serious bug in the code for exponential-related functions that could corrupt the imaginary parts of derivatives, as well as being compatible with a wider range of compilers.

0704.0275

George M. Bergman

George M. Bergman (U.C.Berkeley)

Mapping radii of metric spaces

24 pages. To appear, Pacific J. Math. Any updates, errata, related references etc. learned of after publication will be noted at http://math.berkeley.edu/~gbergman/papers . Changes from first version: correction to display (30) and statement of Cor. 26; new display (41) and Lemma 33; minor clarifications of wording etc.

Pacific J. Math., 236 (2008) 223-261

10.2140/pjm.2008.236.223

math.MG

It is known that every closed curve of length \leq 4 in R^n (n>0) can be surrounded by a sphere of radius 1, and that this is the best bound. Letting S denote the circle of circumference 4, with the arc-length metric, we here express this fact by saying that the "mapping radius" of S in R^n is 1. Tools are developed for estimating the mapping radius of a metric space X in a metric space Y. In particular, it is shown that for X a bounded metric space, the supremum of the mapping radii of X in all convex subsets of normed metric spaces is equal to the infimum of the sup norms of all convex linear combinations of the functions d(x,-): X --> R (x\in X). Several explicit mapping radii are calculated, and open questions noted.

0704.0276

Maik Wolleben

M. Wolleben

A New Model For The Loop-I (The North Polar Spur) Region

17 pages, 6 figures, to appear in ApJ

Astrophys.J.664:349-356,2007

10.1086/518711

astro-ph

The North Polar Spur (NPS) is the brightest filament of Loop I, a large circular feature in the radio continuum sky. In this paper, a model consisting of two synchrotron emitting shells is presented that reproduces large-scale structures revealed by recent polarization surveys. The polarized emission of the NPS is reproduced by one of these shells. The other shell, which passes close to the Sun, gives rise to polarized emission towards the Galactic poles. It is proposed that X-ray emission seen towards the NPS is produced by interaction of the two shells. Two OB-associations coincide with the centers of the shells. A formation scenario of the Loop I region is suggested.

0704.0277

Roy Meshulam

Gil Kalai and Roy Meshulam

Leray numbers of projections and a topological Helly type theorem

9 pages

10.1112/jtopol/jtn010

math.CO

Let X be a simplicial complex on the vertex set V. The rational Leray number L(X) of X is the minimal d such that the rational reduced homology of any induced subcomplex of X vanishes in dimensions d and above. Let \pi be a simplicial map from X to a simplex Y, such that the cardinality of the preimage of any point in |Y| is at most r. It is shown that L(\pi(X)) \leq r L(X)+r-1. One consequence is a topological extension of a Helly type result of Amenta.

0704.0278

Igor Khavkine

Igor Khavkine, J. Daniel Christensen

q-Deformed spin foam models of quantum gravity

21 pages, 6 figures, amsrefs

Class.Quant.Grav.24:3271-3290,2007

10.1088/0264-9381/24/13/009

gr-qc

We numerically study Barrett-Crane models of Riemannian quantum gravity. We have extended the existing numerical techniques to handle q-deformed models and arbitrary space-time triangulations. We present and interpret expectation values of a few selected observables for each model, including a spin-spin correlation function which gives insight into the behaviour of the models. We find the surprising result that, as the deformation parameter q goes to 1 through roots of unity, the limit is discontinuous.

0704.0279

Andreea O. Petric

A. O. Petric and M. P. Rupen

HI velocity dispersion in NGC 1058

29 pages, 16 figures reduced to the lowest qual. to fit the astro-ph size requirements, accepted by AJ

Astron.J.134:1952-1962,2007

10.1086/518558

astro-ph

We present excellent resolution and high sensitivity Very Large Array (VLA) observations of the 21cm HI line emission from the face-on galaxy NGC 1058, providing the first reliable study of the HI profile shapes throughout the entire disk of an external galaxy. Our observations show an intriguing picture of the interstellar medium; throughout this galaxy velocity-- dispersions range between 4 to 15 km/sec but are not correlated with star formation, stars or the gaseous spiral arms. The velocity dispersions decrease with radius, but this global trend has a large scatter as there are several isolated, resolved regions of high dispersion. The decline of star light with radius is much steeper than that of the velocity dispersions or that of the energy in the gas motions.

0704.0280

Ronald F. Webbink

Ronald F. Webbink (University of Illinois at Urbana-Champaign)

Common Envelope Evolution Redux

25 pages, 6 figures. To appear in "Short Period Binary Stars", ed. E.F. Milone, D.A. Leahy, & D.W. Hobill (Springer)

10.1007/978-1-4020-6544-6_13

astro-ph

Common envelopes form in dynamical time scale mass exchange, when the envelope of a donor star engulfs a much denser companion, and the core of the donor plus the dense companion star spiral inward through this dissipative envelope. As conceived by Paczynski and Ostriker, this process must be responsible for the creation of short-period binaries with degenerate components, and, indeed, it has proven capable of accounting for short-period binaries containing one white dwarf component. However, attempts to reconstruct the evolutionary histories of close double white dwarfs have proven more problematic, and point to the need for enhanced systemic mass loss, either during the close of the first, slow episode of mass transfer that produced the first white dwarf, or during the detached phase preceding the final, common envelope episode. The survival of long-period interacting binaries with massive white dwarfs, such as the recurrent novae T CrB and RS Oph, also presents interpretative difficulties for simple energetic treatments of common envelope evolution. Their existence implies that major terms are missing from usual formulations of the energy budget for common envelope evolution. The most plausible missing energy term is the energy released by recombination in the common envelope, and, indeed, a simple reformulation the energy budget explicitly including recombination resolves this issue.

0704.0281

Denis Richard

Denis Richard

The Source of Turbulence in Astrophysical Disks: An Ill-posed Problem.

UCSC-NASA Ames Research Center Workshop on Stellar and Planets Formation March 29, 2007

astro-ph

An critical overview of the current state of research in turbulence in astrophysical disks.

0704.0282

Samuele Bandi

Samuele Bandi, Luca Stabellini, Andrea Conti and Velio Tralli

On Punctured Pragmatic Space-Time Codes in Block Fading Channel

cs.IT cs.CC math.IT

This paper considers the use of punctured convolutional codes to obtain pragmatic space-time trellis codes over block-fading channel. We show that good performance can be achieved even when puncturation is adopted and that we can still employ the same Viterbi decoder of the convolutional mother code by using approximated metrics without increasing the complexity of the decoding operations.

0704.0283

Richard Green

R.M. Green

On the Markov trace for Temperley--Lieb algebras of type $E_n$

Approximately 37 pages, AMSTeX. 9 figures.

math.QA

We show that there is a unique Markov trace on the tower of Temperley--Lieb type quotients of Hecke algebras of Coxeter type $E_n$ (for all $n \geq 6$). We explain in detail how this trace may be computed easily using tom Dieck's calculus of diagrams. As applications, we show how to use the trace to show that the diagram representation is faithful, and to compute leading coefficients of certain Kazhdan--Lusztig polynomials.

0704.0284

Hsien-Chung Kao

Hsien-chung Kao

Second Order Perturbative Calculation of Quasinormal Modes of Schwarzschild Black Holes

12 pages, LaTex

Phys.Rev.D75:124008,2007

10.1103/PhysRevD.75.124008

hep-th gr-qc

We analytically calculate to second order the correction to the asymptotic form of quasinormal frequencies of four dimensional Schwarzschild black holes based on the monodromy analysis proposed by Motl and Neitzke. Our results are in good agreement with those obtained from numerical calculation.

0704.0285

Xiaosong Wu

Walt A. de Heer, Claire Berger, Xiaosong Wu, Phillip N. First, Edward H. Conrad, Xuebin Li, Tianbo Li, Michael Sprinkle, Joanna Hass, Marcin L. Sadowski, Marek Potemski, Gerard Martinez

Epitaxial graphene

19 pages, 11 figures, submitted to Solid State Communications.

Solid State Comm. 143, 92 (2007)

10.1016/j.ssc.2007.04.023

cond-mat.mes-hall cond-mat.mtrl-sci

Graphene multilayers are grown epitaxially on single crystal silicon carbide. This system is composed of several graphene layers of which the first layer is electron doped due to the built-in electric field and the other layers are essentially undoped. Unlike graphite the charge carriers show Dirac particle properties (i.e. an anomalous Berry's phase, weak anti-localization and square root field dependence of the Landau level energies). Epitaxial graphene shows quasi-ballistic transport and long coherence lengths; properties which may persists above cryogenic temperatures. Paradoxically, in contrast to exfoliated graphene, the quantum Hall effect is not observed in high mobility epitaxial graphene. It appears that the effect is suppressed due to absence of localized states in the bulk of the material.Epitaxial graphene can be patterned using standard lithography methods and characterized using a wide array of techniques. These favorable features indicate that interconnected room temperature ballistic devices may be feasible for low dissipation high-speed nanoelectronics.

0704.0286

Peter Kuchment

Peter Kuchment and Leonid Kunyansky

Mathematics of thermoacoustic tomography

Mathematics of Thermoacoustic Tomography, European J. Appl. Math., v. 19, 2008, pp. 1-34.

math.AP math-ph math.MP

The paper presents a survey of mathematical problems, techniques, and challenges arising in the Thermoacoustic and Photoacoustic Tomography.

0704.0287

Pablo M. Saz Parkinson

Pablo M. Saz Parkinson (Milagro Collaboration)

Search for Very High Energy Emission from Gamma-Ray Bursts using Milagro

To appear in "Proceedings of the First International GLAST Symposium", Febuary 5-8, 2007, Stanford University, AIP, Eds. S. Ritz, P. F. Michelson, and C. Meegan

10.1063/1.2757406

astro-ph

Gamma-Ray Bursts (GRBs) have been detected at GeV energies by EGRET and models predict emission at > 100 GeV. Milagro is a wide field (2 sr) high duty cycle (> 90 %) ground based water Cherenkov detector that records extensive air showers in the energy range 100 GeV to 100 TeV. We have searched for very high energy emission from a sample of 106 gamma-ray bursts (GRB) detected since the beginning of 2000 by BATSE, BeppoSax, HETE-2, INTEGRAL, Swift or the IPN. No evidence for emission from any of the bursts has been found and we present upper limits from these bursts.

0704.0288

Gargi Chaudhuri

G. Chaudhuri, S. Das Gupta

Specific heat and bimodality in canonical and grand canonical versions of the thermodynamic model

19 pages, 5 figures

Phys.Rev.C76:014619,2007

10.1103/PhysRevC.76.014619

nucl-th

We address two issues in the thermodynamic model for nuclear disassembly. Surprisingly large differences in results for specific heat were seen in predictions from the canonical and grand canonical ensembles when the nuclear system passes from liquid-gas co-existence to the pure gas phase. We are able to pinpoint and understand the reasons for such and other discrepancies when they appear. There is a subtle but important difference in the physics addressed in the two models. In particular if we reformulate the parameters in the canonical model to better approximate the physics addressed in the grand canonical model, calculations for observables converge. Next we turn to the issue of bimodality in the probability distribution of the largest fragment in both canonical and grand canonical ensembles. We demonstrate that this distribution is very closely related to average multiplicities. The relationship of the bimodal distribution to phase transition is discussed.

0704.0289

Volker Schweikhard

V. Schweikhard, S. Tung, and E. A. Cornell

Vortex proliferation in the Berezinskii-Kosterlitz-Thouless regime on a two-dimensional lattice of Bose-Einstein condensates

changed title; changed definition of vortex density surrogate "D"; additional data in Fig. 3; text revisions

10.1103/PhysRevLett.99.030401

cond-mat.mes-hall

We observe the proliferation of vortices in the Berezinskii-Kosterlitz-Thouless regime on a two-dimensional array of Josephson-coupled Bose-Einstein condensates. As long as the Josephson (tunneling) energy J exceeds the thermal energy T, the array is vortex-free. With decreasing J/T, vortices appear in the system in ever greater numbers. We confirm thermal activation as the vortex formation mechanism and obtain information on the size of bound vortex pairs as J/T is varied.

0704.0290

Jarrod R. Hurley

Jarrod R. Hurley, Sverre J. Aarseth, Michael M. Shara

The core binary fractions of star clusters from realistic simulations

34 pages, 12 figures, accepted for publication in the Astrophysical Journal

Astrophys.J.665:707-718,2007

10.1086/517879

astro-ph

We investigate the evolution of binary fractions in star clusters using N-body models of up to 100000 stars. Primordial binary frequencies in these models range from 5% to 50%. Simulations are performed with the NBODY4 code and include a full mass spectrum of stars, stellar evolution, binary evolution and the tidal field of the Galaxy. We find that the overall binary fraction of a cluster almost always remains close to the primordial value, except at late times when a cluster is near dissolution. A critical exception occurs in the central regions where we observe a marked increase in binary fraction with time -- a simulation starting with 100000 stars and 5% binaries reached a core binary frequency as high as 40% at the end of the core-collapse phase (occurring at 16 Gyr with ~20000 stars remaining). Binaries are destroyed in the core by a variety of processes as a cluster evolves, but the combination of mass-segregation and creation of new binaries in exchange interactions produces the observed increase in relative number. We also find that binaries are cycled into and out of cluster cores in a manner that is analogous to convection in stars. For models of 100000 stars we show that the evolution of the core-radius up to the end of the initial phase of core-collapse is not affected by the exact value of the primordial binary frequency (for frequencies of 10% or less). We discuss the ramifications of our results for the likely primordial binary content of globular clusters.

0704.0291

Matthew Jeppesen

M. Jeppesen, J. Dugu\'e, G. R. Dennis, M. T. Johnsson, C. Figl, N. P. Robins and J. D. Close

Approaching the Heisenberg limit in an atom laser

Corrected analysis, added figure

10.1103/PhysRevA.77.063618

physics.atom-ph cond-mat.other

We present experimental and theoretical results showing the improved beam quality and reduced divergence of an atom laser produced by an optical Raman transition, compared to one produced by an RF transition. We show that Raman outcoupling can eliminate the diverging lens effect that the condensate has on the outcoupled atoms. This substantially improves the beam quality of the atom laser, and the improvement may be greater than a factor of ten for experiments with tight trapping potentials. We show that Raman outcoupling can produce atom lasers whose quality is only limited by the wavefunction shape of the condensate that produces them, typically a factor of 1.3 above the Heisenberg limit.

0704.0292

Gregory Soyez

Gavin P. Salam and Gregory Soyez

A practical Seedless Infrared-Safe Cone jet algorithm

42 pages, 11 figures. SISCone, the C++ implementation of the algorithm, is available at http://projects.hepforge.org/siscone/ (standalone), http://www.lpthe.jussieu.fr/~salam/fastjet/ (FastJet plugin). v2: FastJet URL corrected

JHEP 0705:086,2007

10.1088/1126-6708/2007/05/086

hep-ph

Current cone jet algorithms, widely used at hadron colliders, take event particles as seeds in an iterative search for stable cones. A longstanding infrared (IR) unsafety issue in such algorithms is often assumed to be solvable by adding extra `midpoint' seeds, but actually is just postponed to one order higher in the coupling. A proper solution is to switch to an exact seedless cone algorithm, one that provably identifies all stable cones. The only existing approach takes N 2^N time to find jets among N particles, making it unusable at hadron level. This can be reduced to N^2 ln(N) time, leading to code (SISCone) whose speed is similar to that of public midpoint implementations. Monte Carlo tests provide a strong cross-check of an analytical proof of the IR safety of the new algorithm, and the absence of any 'R_{sep}' issue implies a good practical correspondence between parton and hadron levels. Relative to a midpoint cone, the use of an IR safe seedless algorithm leads to modest changes for inclusive jet spectra, mostly through reduced sensitivity to the underlying event, and significant changes for some multi-jet observables.

0704.0293

Mikhail Voloshin

S. Dubynskiy, A. Le Yaouanc, L. Oliver, J.-C. Raynal and M.B. Voloshin

Isospin breaking in the yield of heavy meson pairs in e+e- annihilation near threshold

16 pages, 2 figures

Phys.Rev.D75:113001,2007

10.1103/PhysRevD.75.113001

FTPI-MINN-07/08, UMN-TH-2541/07, LPT-Orsay/07-19

hep-ph

We revisit the problem of interplay between the strong and the Coulomb interaction in the charged-to-neutral yield ratio for $B {\bar B}$ and $D {\bar D}$ pairs near their respective thresholds in $e^+e^-$ annihilation. We consider here a realistic situation with a resonant interaction in the isospin I=0 channel and a nonresonant strong scattering amplitude in the I=1 state. We find that the yield ratio has a smooth behavior depending on the scattering phase in the I=1 channel. The same approach is also applicable to the $K {\bar K}$ production at the $\phi(1020)$ resonance, where the Coulomb effect in the charged-to-neutral yield ratio is generally sensitive to the scattering phases in both the isoscalar and the isovector channels. Furthermore, we apply the same approach to the treatment of the effect of the isotopic mass difference between the charged and neutral mesons and argue that the strong-scattering effects generally result in a modification to the pure kinematical effect of this mass difference.

0704.0294

Scott A. Yost

B.F.L. Ward and S.A. Yost

QED x QCD Resummation and Shower/ME Matching for LHC Physics

12 pages, LaTex with packages amsmath, amssymb

ActaPhys.Polon.B38:2395-2403,2007

BU-HEPP-07/02

hep-ph

We present the theory of QED x QCD resummation and its interplay with shower/matrix element matching in precision LHC physics scenarios. We illustrate the theory using single heavy gauge boson production at hadron colliders.

0704.0295

Saugata Basu

Saugata Basu

On the number of topological types occurring in a parametrized family of arrangements

20 pages, 2 figures. Revised version with updated bibliography and corrected references

Discrete Comput. Geom. 40:481-503 (2008)

math.CO math.GT

Let ${\mathcal S}(\R)$ be an o-minimal structure over $\R$, $T \subset \R^{k_1+k_2+\ell}$ a closed definable set, and $$ \displaylines{\pi_1: \R^{k_1+k_2+\ell}\to \R^{k_1 + k_2}, \pi_2: \R^{k_1+k_2+\ell}\to \R^{\ell}, \ \pi_3: \R^{k_1 + k_2} \to \R^{k_2}} $$ the projection maps. For any collection ${\mathcal A} = \{A_1,...,A_n\}$ of subsets of $\R^{k_1+k_2}$, and $\z \in \R^{k_2}$, let $\A_\z$ denote the collection of subsets of $\R^{k_1}$, $\{A_{1,\z},..., A_{n,\z}\}$, where $A_{i,\z} = A_i \cap \pi_3^{-1}(\z), 1 \leq i \leq n$. We prove that there exists a constant $C = C(T) > 0,$ such that for any family ${\mathcal A} = \{A_1,...,A_n\}$ of definable sets, where each $A_i = \pi_1(T \cap \pi_2^{-1}(\y_i))$, for some $\y_i \in \R^{\ell}$, the number of distinct stable homotopy types of $\A_\z, \z \in \R^{k_2}$, is bounded by $ \displaystyle{C \cdot n^{(k_1+1)k_2},} $ while the number of distinct homotopy types is bounded by $ \displaystyle{C \cdot n^{(k_1+3)k_2}.} $ This generalizes to the general o-minimal setting, bounds of the same type proved in \cite{BV} for semi-algebraic and semi-Pfaffian families. One main technical tool used in the proof of the above results, is a topological comparison theorem which might be of independent interest in the study of arrangements.

0704.0296

Itzhak Bars

Itzhak Bars and Bora Orcal

Generalized Twistor Transform And Dualities, With A New Description of Particles With Spin, Beyond Free and Massless

33 pages

Phys.Rev.D75:104015,2007

10.1103/PhysRevD.75.104015

USC-07/HEP-B3

hep-th

A generalized twistor transform for spinning particles in 3+1 dimensions is constructed that beautifully unifies many types of spinning systems by mapping them to the same twistor, thus predicting an infinite set of duality relations among spinning systems with different Hamiltonians. Usual 1T-physics is not equipped to explain the duality relationships and unification between these systems. We use 2T-physics in 4+2 dimensions to uncover new properties of twistors, and expect that our approach will prove to be useful for practical applications as well as for a deeper understanding of fundamental physics. Unexpected structures for a new description of spinning particles emerge. A unifying symmetry SU(2,3) that includes conformal symmetry SU(2,2)=SO(4,2) in the massless case, turns out to be a fundamental property underlying the dualities of a large set of spinning systems, including those that occur in high spin theories. This may lead to new forms of string theory backgrounds as well as to new methods for studying various corners of M theory. In this paper we present the main concepts, and in a companion paper we give other details.

0704.0297

Sung-Chul Yoon

Sung-Chul Yoon, Philipp Podsiadlowski and Stephan Rosswog

Remnant evolution after a carbon-oxygen white dwarf merger

15 pages, 15 figures, 3 tables, submitted to MNRAS (Low resolution version; a high resolution version can be found at: http://www.astro.uva.nl/~scyoon/papers/wdmerger.pdf)

10.1111/j.1365-2966.2007.12161.x

astro-ph

We systematically explore the evolution of the merger of two carbon-oxygen (CO) white dwarfs. The dynamical evolution of a 0.9 Msun + 0.6 Msun CO white dwarf merger is followed by a three-dimensional SPH simulation. We use an elaborate prescription in which artificial viscosity is essentially absent, unless a shock is detected, and a much larger number of SPH particles than earlier calculations. Based on this simulation, we suggest that the central region of the merger remnant can, once it has reached quasi-static equilibrium, be approximated as a differentially rotating CO star, which consists of a slowly rotating cold core and a rapidly rotating hot envelope surrounded by a centrifugally supported disc. We construct a model of the CO remnant that mimics the results of the SPH simulation using a one-dimensional hydrodynamic stellar evolution code and then follow its secular evolution. The stellar evolution models indicate that the growth of the cold core is controlled by neutrino cooling at the interface between the core and the hot envelope, and that carbon ignition in the envelope can be avoided despite high effective accretion rates. This result suggests that the assumption of forced accretion of cold matter that was adopted in previous studies of the evolution of double CO white dwarf merger remnants may not be appropriate. Our results imply that at least some products of double CO white dwarfs merger may be considered good candidates for the progenitors of Type Ia supernovae. In this case, the characteristic time delay between the initial dynamical merger and the eventual explosion would be ~10^5 yr. (Abridged).

0704.0298

Sergiy Torba M.

Ya. Grushka and S. Torba

Direct Theorems in the Theory of Approximation of the Banach Space Vectors by Entire Vectors of Exponential Type

13 pages, typos corrected

Grushka Ya. and Torba S., "Direct Theorems in the Theory of Approximation of Banach Space Vectors by Exponential Type Entire Vectors", Methods Funct. Anal. Topology. 11 (2007), no. 3, 267-278

math.FA math.SP

http://arxiv.org/licenses/nonexclusive-distrib/1.0/

For an arbitrary operator A on a Banach space X which is a generator of C_0-group with certain growth condition at the infinity, the direct theorems on connection between the smoothness degree of a vector $x\in X$ with respect to the operator A, the order of convergence to zero of the best approximation of x by exponential type entire vectors for the operator A, and the k-module of continuity are given. Obtained results allows to acquire Jackson-type inequalities in many classic spaces of periodic functions and weighted $L_p$ spaces.

0704.0299

Nicolas Yunes

Stephon Alexander and Nicolas Yunes

Parametrized Post-Newtonian Expansion of Chern-Simons Gravity

14 pagges

Phys.Rev.D75:124022,2007

10.1103/PhysRevD.75.124022

IGPG-07/4-1

hep-th astro-ph gr-qc

We investigate the weak-field, post-Newtonian expansion to the solution of the field equations in Chern-Simons gravity with a perfect fluid source. In particular, we study the mapping of this solution to the parameterized post-Newtonian formalism to 1 PN order in the metric. We find that the PPN parameters of Chern-Simons gravity are identical to those of general relativity, with the exception of the inclusion of a new term that is proportional to the Chern-Simons coupling parameter and the curl of the PPN vector potentials. We also find that the new term is naturally enhanced by the non-linearity of spacetime and we provide a physical interpretation for it. By mapping this correction to the gravito-electro-magnetic framework, we study the corrections that this new term introduces to the acceleration of point particles and the frame-dragging effect in gyroscopic precession. We find that the Chern-Simons correction to these classical predictions could be used by current and future experiments to place bounds on intrinsic parameters of Chern-Simons gravity and, thus, string theory.

0704.0300

Philip Kim

Meninder Purewal, Byung Hee Hong, Anirudhh Ravi, Bhupesh Chandra, James Hone, and Philip Kim

Scaling of Resistance and Electron Mean Free Path of Single-Walled Carbon Nanotubes

4 pages 4 figures, to appear in Phys. Rev. Lett

Phys. Rev. Lett, 98, 186808 (2007)

10.1103/PhysRevLett.98.186808

cond-mat.mes-hall cond-mat.mtrl-sci

We present an experimental investigation on the scaling of resistance in individual single walled carbon nanotube devices with channel lengths that vary four orders of magnitude on the same sample. The electron mean free path is obtained from the linear scaling of resistance with length at various temperatures. The low temperature mean free path is determined by impurity scattering, while at high temperature the mean free path decreases with increasing temperature, indicating that it is limited by electron-phonon scattering. An unusually long mean free path at room temperature has been experimentally confirmed. Exponentially increasing resistance with length at extremely long length scales suggests anomalous localization effects.