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0704.1601 | Spontaneous symmetry breaking of solitons trapped in a double-channel
potential | We consider a two-dimensional (2D) nonlinear Schrodinger equation with
self-focusing nonlinearity and a quasi-1D double-channel potential, i.e., a
straightforward 2D extension of the well-known double-well potential. The model
may be realized in terms of nonlinear optics and Bose-Einstein condensates. The
variational approximation (VA) predicts a bifurcation breaking the symmetry of
2D solitons trapped in the double channel, the bifurcation being of the
subcritical type. The predictions of the VA are confirmed by numerical
simulations. The work presents the first example of the spontaneous symmetry
breaking (SSB) of 2D solitons in any dual-core system.
| nlin.PS |
0704.1602 | What does Hirsch index evolution explain us? A case study: Turkish
Journal of Chemistry | The evolution of Turkish Journal of Chemistry (Turk J. Chem) Hirsch index
(h-index) over the period 1995-2005 is studied and determined in the case of
the self and without self-citations. It is seen that the effect of Hirsch index
of Turk J. Chem has a highly positive trend during the last five years. It
proves that Turk J. Chem is improving itself both in quantity and quality since
h-index reflects peer review, and peer review reflects research quality of a
journal.
| physics.ed-ph physics.soc-ph |
0704.1603 | Measuring energy dependent polarization in soft gamma-rays using Compton
scattering in PoGOLite | Linear polarization in X- and gamma-rays is an important diagnostic of many
astrophysical sources, foremost giving information about their geometry,
magnetic fields, and radiation mechanisms. However, very few X-ray polarization
measurements have been made, and then only mono-energetic detections, whilst
several objects are assumed to have energy dependent polarization signatures.
In this paper we investigate whether detection of energy dependent polarization
from cosmic sources is possible using the Compton technique, in particular with
the proposed PoGOLite balloon-experiment, in the 25-100 keV range. We use
Geant4 simulations of a PoGOLite model and input photon spectra based on Cygnus
X-1 and accreting magnetic pulsars (100 mCrab). Effective observing times of 6
and 35 hours were simulated, corresponding to a standard and a long duration
flight respectively. Both smooth and sharp energy variations of the
polarization are investigated and compared to constant polarization signals
using chi-square statistics. We can reject constant polarization, with energy,
for the Cygnus X-1 spectrum (in the hard state), if the reflected component is
assumed to be completely polarized, whereas the distinction cannot be made for
weaker polarization. For the accreting pulsar, constant polarization can be
rejected in the case of polarization in a narrow energy band with at least 50%
polarization, and similarly for a negative step distribution from 30% to 0%
polarization.
| astro-ph |
0704.1604 | Baryon Number-Induced Chern-Simons Couplings of Vector and Axial-Vector
Mesons in Holographic QCD | We show that holographic models of QCD predict the presence of a Chern-Simons
coupling between vector and axial-vector mesons at finite baryon density. In
the AdS/CFT dictionary, the coefficient of this coupling is proportional to the
baryon number density, and is fixed uniquely in the five-dimensional
holographic dual by anomalies in the flavor currents. For the lightest mesons,
the coupling mixes transverse $\rho$ and $a_1$ polarization states. At
sufficiently large baryon number densities, it produces an instability, which
causes the $\rho$ and $a_1$ mesons to condense in a state breaking both
rotational and translational invariance.
| hep-ph hep-th |
0704.1605 | Total Quantum Zeno Effect beyond Zeno Time | In this work we show that is possible to obtain Total Quantum Zeno Effect in
an unstable systems for times larger than the correlation time of the bath. The
effect is observed for some particular systems in which one can chose
appropriate observables which frequent measurements freeze the system into the
initial state. For a two level system in a squeezed bath one can show that
there are two bath dependent observables displaying Total Zeno Effect when the
system is initialized in some particular states. We show also that these states
are intelligent states of two conjugate observables associated to the
electromagnetic fluctuations of the bath.
| quant-ph |
0704.1606 | Asteroseismic Signatures of Stellar Magnetic Activity Cycles | Observations of stellar activity cycles provide an opportunity to study
magnetic dynamos under many different physical conditions. Space-based
asteroseismology missions will soon yield useful constraints on the interior
conditions that nurture such magnetic cycles, and will be sensitive enough to
detect shifts in the oscillation frequencies due to the magnetic variations. We
derive a method for predicting these shifts from changes in the Mg II activity
index by scaling from solar data. We demonstrate this technique on the
solar-type subgiant beta Hyi, using archival International Ultraviolet Explorer
spectra and two epochs of ground-based asteroseismic observations. We find
qualitative evidence of the expected frequency shifts and predict the optimal
timing for future asteroseismic observations of this star.
| astro-ph |
0704.1607 | Anomalous energy transport in the FPU-beta chain | We consider the energy current correlation function for the FPU-beta lattice.
For small non-linearity one can rely on kinetic theory. The issue reduces then
to a spectral analysis of the linearized collision operator. We prove thereby
that, on the basis of kinetic theory, the energy current correlations decay in
time as t^(-3/5). It follows that the thermal conductivity is anomalous,
increasing as N^(2/5) with the system size N.
| math-ph math.MP |
0704.1608 | Diffractive parton distributions from the analysis with higher twist | Diffractive parton distributions of the proton are determined from fits to
diffractive data from HERA. In addition to the twist--2 contribution, the
twist--4 contribution from longitudinally polarised virtual photons is
considered, which is important in the region of small diffractive masses. A new
prediction for the longitudinal diffractive structure function is presented
which differs significantly from that obtained in the pure twist--2 analyses.
| hep-ph |
0704.1609 | GRB 061121: Broadband spectral evolution through the prompt and
afterglow phases of a bright burst | Swift triggered on a precursor to the main burst of GRB 061121 (z=1.314),
allowing observations to be made from the optical to gamma-ray bands. Many
other telescopes, including Konus-Wind, XMM-Newton, ROTSE and the Faulkes
Telescope North, also observed the burst. The gamma-ray, X-ray and UV/optical
emission all showed a peak ~75s after the trigger, although the optical and
X-ray afterglow components also appear early on - before, or during, the main
peak. Spectral evolution was seen throughout the burst, with the prompt
emission showing a clear positive correlation between brightness and hardness.
The Spectral Energy Distribution (SED) of the prompt emission, stretching from
1eV up to 1MeV, is very flat, with a peak in the flux density at ~1keV. The
optical-to-X-ray spectra at this time are better fitted by a broken, rather
than single, power-law, similar to previous results for X-ray flares. The SED
shows spectral hardening as the afterglow evolves with time. This behaviour
might be a symptom of self-Comptonisation, although circumstellar densities
similar to those found in the cores of molecular clouds would be required. The
afterglow also decays too slowly to be accounted for by the standard models.
Although the precursor and main emission show different spectral lags, both are
consistent with the lag-luminosity correlation for long bursts. GRB 061121 is
the instantaneously brightest long burst yet detected by Swift. Using a
combination of Swift and Konus-Wind data, we estimate an isotropic energy of
2.8x10^53 erg over 1keV - 10MeV in the GRB rest frame. A probable jet break is
detected at ~2x10^5s, leading to an estimate of ~10^51 erg for the
beaming-corrected gamma-ray energy.
| astro-ph |
0704.1610 | High-altitude signatures of ionospheric density depletions caused by
field-aligned currents | We present Cluster measurements of large electric fields correlated with
intense downward field-aligned currents, and show that the data can be
reproduced by a simple model of ionospheric plasma depletion caused by the
currents. This type of magnetosphere-ionosphere interaction may be important
when considering the mapping between these two regions of space.
| physics.space-ph physics.plasm-ph |
0704.1611 | Burgers Turbulence | The last decades witnessed a renewal of interest in the Burgers equation.
Much activities focused on extensions of the original one-dimensional
pressureless model introduced in the thirties by the Dutch scientist J.M.
Burgers, and more precisely on the problem of Burgers turbulence, that is the
study of the solutions to the one- or multi-dimensional Burgers equation with
random initial conditions or random forcing. Such work was frequently motivated
by new emerging applications of Burgers model to statistical physics,
cosmology, and fluid dynamics. Also Burgers turbulence appeared as one of the
simplest instances of a nonlinear system out of equilibrium. The study of
random Lagrangian systems, of stochastic partial differential equations and
their invariant measures, the theory of dynamical systems, the applications of
field theory to the understanding of dissipative anomalies and of multiscaling
in hydrodynamic turbulence have benefited significantly from progress in
Burgers turbulence. The aim of this review is to give a unified view of
selected work stemming from these rather diverse disciplines.
| nlin.CD |
0704.1612 | Analytical evaluation of the X-ray scattering contribution to imaging
degradation in grazing-incidence X-ray telescopes | The focusing performance of X-ray optics (conveniently expressed in terms of
HEW, Half Energy Width) strongly depend on both mirrors deformations and photon
scattering caused by the microroughness of reflecting surfaces. In particular,
the contribution of X-ray Scattering (XRS) to the HEW of the optic is usually
an increasing function H(E) of the photon energy E. Therefore, in future hard
X-ray imaging telescopes of the future (SIMBOL-X, NeXT, Constellation-X, XEUS),
the X-ray scattering could be the dominant problem since they will operate also
in the hard X-ray band (i.e. beyond 10 keV). [...]
Several methods were proposed in the past years to estimate the scattering
contribution to the HEW, dealing with the surface microroughness expressed in
terms of its Power Spectral Density (PSD), on the basis of the well-established
theory of X-ray scattering from rough surfaces. We faced that problem on the
basis on the same theory, but we tried a new approach: the direct, analytical
translation of a given surface roughness PSD into a H(E) trend, and - vice
versa - the direct translation of a H(E) requirement into a surface PSD. This
PSD represents the maximum tolerable microroughness level in order to meet the
H(E) requirement in the energy band of a given X-ray telescope.
We have thereby found a new, analytical and widely applicable formalism to
compute the XRS contribution to the HEW from the surface PSD, provided that the
PSD had been measured in a wide range of spatial frequencies. The inverse
problem was also solved, allowing the immediate evaluation of the mirror
surface PSD from a measured function H(E). The same formalism allows
establishing the maximum allowed PSD of the mirror in order to fulfill a given
H(E) requirement. [...]
| astro-ph |
0704.1613 | Reply to ``Comment on `On the inconsistency of the Bohm-Gadella theory
with quantum mechanics''' | In this reply, we show that when we apply standard distribution theory to the
Lippmann-Schwinger equation, the resulting spaces of test functions would
comply with the Hardy axiom only if classic results of Paley and Wiener, of
Gelfand and Shilov, and of the theory of ultradistributions were wrong. As
well, we point out several differences between the ``standard method'' of
constructing rigged Hilbert spaces in quantum mechanics and the method used in
Time Asymmetric Quantum Theory.
| quant-ph hep-th math-ph math.MP |
0704.1614 | Modelling the Galactic bar using OGLE-II Red Clump Giant Stars | Red clump giant stars can be used as distance indicators to trace the mass
distribution of the Galactic bar. We use RCG stars from 44 bulge fields from
the OGLE-II microlensing collaboration database to constrain analytic tri-axial
models for the Galactic bar. We find the bar major axis is oriented at an angle
of 24 - 27 degrees to the Sun-Galactic centre line-of-sight. The ratio of
semi-major and semi-minor bar axis scale lengths in the Galactic plane x_0,
y_0, and vertical bar scale length z_0, is x_0 : y_0 : z_0 = 10 : 3.5 : 2.6,
suggesting a slightly more prolate bar structure than the working model of
Gerhard (2002) which gives the scale length ratios as x_0 : y_0 : z_0 = 10 : 4
: 3 .
| astro-ph |
0704.1615 | Dynamical Coupled-Channel Model of $\pi N$ Scattering in the W $\leq$ 2
GeV Nucleon Resonance Region | As a first step to analyze the electromagnetic meson production reactions in
the nucleon resonance region, the parameters of the hadronic interactions of a
dynamical coupled-channel model, developed in {\it Physics Reports 439, 193
(2007)}, are determined by fitting the $\pi N$ scattering data. The channels
included in the calculations are $\pi N$, $\eta N$ and $\pi\pi N$ which has
$\pi\Delta$, $\rho N$, and $\sigma N$ resonant components. The non-resonant
meson-baryon interactions of the model are derived from a set of Lagrangians by
using a unitary transformation method. One or two bare excited nucleon states
in each of $S$, $P$, $D$, and $F$ partial waves are included to generate the
resonant amplitudes in the fits. The parameters of the model are first
determined by fitting as much as possible the empirical $\pi N$ elastic
scattering amplitudes of SAID up to 2 GeV. We then refine and confirm the
resulting parameters by directly comparing the predicted differential cross
section and target polarization asymmetry with the original data of the elastic
$\pi^{\pm} p \to \pi^{\pm} p$ and charge-exchange $\pi^- p \to \pi^0 n$
processes. The predicted total cross sections of $\pi N$ reactions and $\pi
N\to \eta N$ reactions are also in good agreement with the data. Applications
of the constructed model in analyzing the electromagnetic meson production data
as well as the future developments are discussed.
| nucl-th |
0704.1616 | Reply to Comment on "Chiral suppression of scalar glueball decay" | Reply to the comment of Chao, He, and Ma.
| hep-ph |
0704.1617 | High-resolution study of a star-forming cluster in the Cep-A HW2 region | Due to its relatively small distance (725 pc), the Cepheus A East
star-forming region is an ideal laboratory to study massive star formation
processes. Based on its morphology, it has been suggested that the flattened
molecular gas distribution around the YSO HW2 may be a 350-AU-radius massive
protostellar disk. Goal of our work is to ascertain the nature of this
structure. We have employed the Plateau de Bure Interferometer to acquire
(sub-)arcsecond-resolution imaging of high-density and shock tracers, such as
methyl cyanide (CH3CN) and silicon monoxide (SiO), towards the HW2 position. On
the 1-arcsecond (about 725 AU) scale, the flattened distribution of molecular
gas around HW2 appears to be due to the projected superposition, on the plane
of the sky, of at least three protostellar objects, of which at least one is
powering a molecular outflow at a small angle with respect to the line of
sight. The presence of a protostellar disk around HW2 is not ruled out, but
such structure is likely to be detected on a smaller spatial scale, or using
different molecular tracers.
| astro-ph |
0704.1618 | A Renormalization group approach for highly anisotropic 2D Fermion
systems: application to coupled Hubbard chains | I apply a two-step density-matrix renormalization group method to the
anisotropic two-dimensional Hubbard model. As a prelude to this study, I
compare the numerical results to the exact one for the tight-binding model. I
find a ground-state energy which agrees with the exact value up to four digits
for systems as large as $24 \times 25$. I then apply the method to the
interacting case. I find that for strong Hubbard interaction, the ground-state
is dominated by magnetic correlations.
These correlations are robust even in the presence of strong frustration.
Interchain pair tunneling is negligible in the singlet and triplet channels and
it is not enhanced by frustration. For weak Hubbard couplings, interchain
non-local singlet pair tunneling is enhanced and magnetic correlations are
strongly reduced. This suggests a possible superconductive ground state.
| cond-mat.str-el cond-mat.supr-con |
0704.1619 | Proper Motion Dispersions of Red Clump Giants in the Galactic Bulge:
Observations and Model Comparisons | Red clump giants in the Galactic bulge are approximate standard candles and
hence they can be used as distance indicators. We compute the proper motion
dispersions of RCG stars in the Galactic bulge using the proper motion
catalogue from the second phase of the Optical Gravitational Microlensing
Experiment (OGLE-II, Sumi et al. 2004) for 45 fields. The proper motion
dispersions are measured to a few per cent accuracy due to the large number of
stars in the fields. The observational sample is comprised of 577736 stars.
These observed data are compared to a state-of-the-art particle simulation of
the Galactic bulge region. The predictions are in rough agreement with
observations, but appear to be too anisotropic in the velocity ellipsoid. We
note that there is significant field-to-field variation in the observed proper
motion dispersions. This could either be a real feature, or due to some unknown
systematic effect.
| astro-ph |
0704.1620 | Intramolecular long-range correlations in polymer melts: The segmental
size distribution and its moments | Presenting theoretical arguments and numerical results we demonstrate
long-range intrachain correlations in concentrated solutions and melts of long
flexible polymers which cause a systematic swelling of short chain segments.
They can be traced back to the incompressibility of the melt leading to an
effective repulsion $u(s) \approx s/\rho R^3(s) \approx ce/\sqrt{s}$ when
connecting two segments together where $s$ denotes the curvilinear length of a
segment, $R(s)$ its typical size, $ce \approx 1/\rho be^3$ the ``swelling
coefficient", $be$ the effective bond length and $\rho$ the monomer density.
The relative deviation of the segmental size distribution from the ideal
Gaussian chain behavior is found to be proportional to $u(s)$. The analysis of
different moments of this distribution allows for a precise determination of
the effective bond length $be$ and the swelling coefficient $ce$ of
asymptotically long chains. At striking variance to the short-range decay
suggested by Flory's ideality hypothesis the bond-bond correlation function of
two bonds separated by $s$ monomers along the chain is found to decay
algebraically as $1/s^{3/2}$. Effects of finite chain length are considered
briefly.
| cond-mat.soft |
0704.1621 | Stability Properties of Strongly Magnetized Spine Sheath Relativistic
Jets | The linearized relativistic magnetohydrodynamic (RMHD) equations describing a
uniform axially magnetized cylindrical relativistic jet spine embedded in a
uniform axially magnetized relativistically moving sheath are derived. The
displacement current is retained in the equations so that effects associated
with Alfven wave propagation near light speed can be studied. A dispersion
relation for the normal modes is obtained. Analytical solutions for the normal
modes in the low and high frequency limits are found and a general stability
condition is determined. A trans-Alfvenic and even a super-Alfvenic
relativistic jet spine can be stable to velocity shear driven Kelvin-Helmholtz
modes. The resonance condition for maximum growth of the normal modes is
obtained in the kinetically and magnetically dominated regimes. Numerical
solution of the dispersion relation verifies the analytical solutions and is
used to study the regime of high sound and Alfven speeds.
| astro-ph |
0704.1622 | MATLAB codes for teaching quantum physics: Part 1 | Among the ideas to be conveyed to students in an introductory quantum course,
we have the pivotal idea championed by Dirac that functions correspond to
column vectors (kets) and that differential operators correspond to matrices
(ket-bras) acting on those vectors. The MATLAB (matrix-laboratory) programming
environment is especially useful in conveying these concepts to students
because it is geared towards the type of matrix manipulations useful in solving
introductory quantum physics problems. In this article, we share MATLAB codes
which have been developed at WPI, focusing on 1D problems, to be used in
conjunction with Griffiths' introductory text.
| physics.ed-ph physics.comp-ph |
0704.1623 | Nanodevices and Maxwell's Demon | In the last twenty years there has been significant progress in our
understanding of quantum transport far from equilibrium and a conceptual
framework has emerged through a combination of the Landauer approach with the
non-equilibrium Green function (NEGF) method, which is now being widely used in
the analysis and design of nanoscale devices. It provides a unified description
for all kinds of devices from molecular conductors to carbon nanotubes to
silicon transistors covering different transport regimes from the ballistic to
the diffusive limit. In this talk I use a simple version of this model to
analyze a specially designed device that could be called an electronic
Maxwell's demon, one that lets electrons go preferentially in one direction
over another. My objective is to illustrate the fundamental role of contacts
and demons in transport and energy conversion. The discussion is kept at an
academic level steering clear of real world details, but the illustrative
devices we use are very much within the capabilities of present-day technology.
For example, recent experiments on thermoelectric effects in molecular
conductors agree well with the predictions from our model. The Maxwell's demon
device itself is very similar to the pentalayer spin-torque device which has
been studied by a number of groups though we are not aware of any discussion of
the possibility of using the device as a nanoscale heat engine or as a
refrigerator as proposed here. However, my objective is not to evaluate
possible practical applications. Rather it is to introduce a simple transparent
model showing how out-of-equibrium demons suitably incorporated into
nanodevices can achieve energy conversion.
| cond-mat.mes-hall |
0704.1624 | Complete Segal spaces arising from simplicial categories | In this paper, we compare several functors which take simplicial categories
or model categories to complete Segal spaces, which are particularly nice
simplicial spaces which, like simplicial categories, can be considered to be
models for homotopy theories. We then give a characterization, up to weak
equivalence, of complete Segal spaces arising from these functors.
| math.AT math.CT |
0704.1625 | A Systematic Scan for 7-colourings of the Grid | We study the mixing time of a systematic scan Markov chain for sampling from
the uniform distribution on proper 7-colourings of a finite rectangular
sub-grid of the infinite square lattice, the grid. A systematic scan Markov
chain cycles through finite-size subsets of vertices in a deterministic order
and updates the colours assigned to the vertices of each subset. The systematic
scan Markov chain that we present cycles through subsets consisting of 2x2
sub-grids and updates the colours assigned to the vertices using a procedure
known as heat-bath. We give a computer-assisted proof that this systematic scan
Markov chain mixes in O(log n) scans, where n is the size of the rectangular
sub-grid. We make use of a heuristic to compute required couplings of
colourings of 2x2 sub-grids. This is the first time the mixing time of a
systematic scan Markov chain on the grid has been shown to mix for less than 8
colours. We also give partial results that underline the challenges of proving
rapid mixing of a systematic scan Markov chain for sampling 6-colourings of the
grid by considering 2x3 and 3x3 sub-grids.
| math.PR |
0704.1626 | Magnetic exponents of two-dimensional Ising spin glasses | The magnetic critical properties of two-dimensional Ising spin glasses are
controversial. Using exact ground state determination, we extract the
properties of clusters flipped when increasing continuously a uniform field. We
show that these clusters have many holes but otherwise have statistical
properties similar to those of zero-field droplets. A detailed analysis gives
for the magnetization exponent delta = 1.30 +/- 0.02 using lattice sizes up to
80x80; this is compatible with the droplet model prediction delta = 1.282. The
reason for previous disagreements stems from the need to analyze both singular
and analytic contributions in the low-field regime.
| cond-mat.dis-nn |
0704.1627 | Thin elastic shells with variable thickness for lithospheric flexure of
one-plate planets | Planetary topography can either be modeled as a load supported by the
lithosphere, or as a dynamical effect due to lithospheric flexure caused by
mantle convection. In both cases the response of the lithosphere to external
forces can be calculated with the theory of thin elastic plates or shells. On
one-plate planets the spherical geometry of the lithospheric shell plays an
important role in the flexure mechanism. So far the equations governing the
deformations and stresses of a spherical shell have only been derived under the
assumption of a shell of constant thickness. However local studies of gravity
and topography data suggest large variations in the thickness of the
lithosphere. In this article we obtain the scalar flexure equations governing
the deformations of a thin spherical shell with variable thickness or variable
Young's modulus. The resulting equations can be solved in succession, except
for a system of two simultaneous equations, the solutions of which are the
transverse deflection and an associated stress function. In order to include
bottom loading generated by mantle convection, we extend the method of stress
functions to include loads with a toroidal tangential component. We further
show that toroidal tangential displacement always occurs if the shell thickness
varies, even in the absence of toroidal loads. We finally prove that the
degree-one harmonic components of the transverse deflection and of the toroidal
tangential displacement are independent of the elastic properties of the shell
and are associated with translational and rotational freedom. The flexure
equations for a shell of variable thickness are useful not only for the
prediction of the gravity signal in local admittance studies, but also for the
construction of stress maps in tectonic analysis.
| physics.geo-ph physics.space-ph |
0704.1628 | Detection of single electron spin resonance in a double quantum dot | Spin-dependent transport measurements through a double quantum dot are a
valuable tool for detecting both the coherent evolution of the spin state of a
single electron as well as the hybridization of two-electron spin states. In
this paper, we discuss a model that describes the transport cycle in this
regime, including the effects of an oscillating magnetic field (causing
electron spin resonance) and the effective nuclear fields on the spin states in
the two dots. We numerically calculate the current flow due to the induced spin
flips via electron spin resonance and we study the detector efficiency for a
range of parameters. The experimental data are compared with the model and we
find a reasonable agreement.
| cond-mat.mes-hall |
0704.1629 | Donor type semiconductor at low temperature as maser active medium | In some semiconductors donor impurity atoms can attract additional electrons,
forming negative donor impurity ions. Thus we have 3 energy levels for
electrons: zero energy levels at the bottom of the conductivity band, negative
energy levels of the bounded electrons of the negative donor impurity ions, and
deeper negative energy levels of the outer electrons of the neutral donor
impurity atoms. So the donor impurity atoms could serve as active centres for a
maser. The maximum achievable relative population is 0.5. Typical wavelength of
the generated oscillation is 0.14 mm; three level scheme could be realized at
rather low temperatures, considerably lower than 6 K.
| cond-mat.mtrl-sci |
0704.1630 | Exciting the Magnetosphere of the Magnetar CXOU J164710.2-455216 in
Westerlund 1 | We describe XMM-Newton observations taken 4.3 days prior to and 1.5 days
subsequent to two remarkable events that were detected with Swift on 2006
September 21 from the candidate magnetar CXOU J164710.2-455216: (1) a 20 ms
burst with an energy of 1e37 erg (15-150 keV), and (2) a rapid spin-down
(glitch) with a fractionap period change of 1e-4. We find that the luminosity
of the pulsar increased by a factor of 100 in the interval between
observations, from 1e33 to 1e35 erg/s (0.5-8.0 keV), and that its spectrum
hardened. The pulsed count rate increased by a factor of 10 (0.5-8.0 keV), but
the fractional rms amplitude of the pulses decreased from 65 to 11 per cent,
and their profile changed from being single-peaked to exhibiting three peaks.
Similar changes have been observed from other magnetars in response to
outbursts, such as that of 1E 2259+586 in 2002 June. We suggest that a plastic
deformation of the neutron star's crust induced a very slight twist in the
external magnetic field, which in turn generated currents in the magnetosphere
that were the direct cause of the X-ray outburst.
| astro-ph |
0704.1631 | Further Evidence that the Redshifts of AGN Galaxies May Contain
Intrinsic Components | In the decreasing intrinsic redshift (DIR) model galaxies are assumed to be
born as compact objects that have been ejected with large intrinsic redshift
components, z_(i), out of the nuclei of mature AGN galaxies. As young AGN
(quasars) they are initially several magnitudes sub-luminous to mature galaxies
but their luminosity gradually increases over 10^8 yrs, as z_(i) decreases and
they evolve into mature AGN (Seyferts and radio galaxies). Evidence presented
here that low- and intermediate-redshift AGN are unquestionably sub-luminous to
radio galaxies is then strong support for this model and makes it likely that
the high-redshift AGN (quasars) are also sub-luminous, having simply been
pushed above the radio galaxies on a logz-m_(v) plot by the presence of a large
intrinsic component in their redshifts. An increase in luminosity below z =
0.06 is also seen. It is associated in the DIR model with an increase in
luminosity as the sources mature but, if real, is difficult to interpret in the
cosmological redshift (CR) model since at this low redshift it is unlikely to
be associated with a higher star formation rate or an increase in the material
used to build galaxies. Whether it might be possible in the CR model to explain
these results by selection effects is also examined.
| astro-ph |
0704.1632 | Semiclassical scattering amplitude at the maximum point of the potential | We compute the scattering amplitude for Schr\"odinger operators at a critical
energy level, corresponding to the maximum point of the potential. We follow
the wrok of Robert and Tamura, '89, using Isozaki and Kitada's representation
formula for the scattering amplitude, together with results from Bony, Fujiie,
Ramond and Zerzeri '06 in order to analyze the contribution of trapped
trajectories.
| math.AP math-ph math.MP |
0704.1633 | Hilbert Spaces with Generic Predicates | We study the model theory of expansions of Hilbert spaces by generic
predicates. We first prove the existence of model companions for generic
expansions of Hilbert spaces in the form first of a distance function to a
random substructure, then a distance to a random subset. The theory obtained
with the random substructure is {\omega}-stable, while the one obtained with
the distance to a random subset is $TP_2$ and $NSOP_1$. That example is the
first continuous structure in that class.
| math.LO |
0704.1634 | Riggings of locally compact abelian groups | We obtain a set of generalized eigenvectors that provides a generalized
spectral decomposition for a given unitary representation of a commutative,
locally compact topological group. These generalized eigenvectors are
functionals belonging to the dual space of a rigging on the space of square
integrable functions on the character group. These riggings are obtained
through suitable spectral measure spaces.
| math-ph math.MP |
0704.1635 | Weak Amenability of Hyperbolic Groups | We prove that hyperbolic groups are weakly amenable. This partially extends
the result of Cowling and Haagerup showing that lattices in simple Lie groups
of real rank one are weakly amenable. We take a combinatorial approach in the
spirit of Haagerup and prove that for the word length metric d on a hyperbolic
group, the Schur multipliers associated with r^d have uniformly bounded norms
for 0<r<1. We then combine this with a Bozejko-Picardello type inequality to
obtain weak amenability.
| math.FA math.GR |
0704.1636 | Light Curves of Dwarf Plutonian Planets and other Large Kuiper Belt
Objects: Their Rotations, Phase Functions and Absolute Magnitudes | (Abridged) I report new light curves and determine the rotations and phase
functions of several large Kuiper Belt objects, including the dwarf planet Eris
(2003 UB313). (120348) 2004 TY364 shows a light curve which if double-peaked
has a period of 11.70+-0.01 hours and peak-to-peak amplitude of 0.22+-0.02
magnitudes. (84922) 2003 VS2 has a well defined double-peaked light curve of
7.41+-0.02 hours with a 0.21+-0.02 magnitude range. (126154) 2001 YH140 shows
variability of 0.21+-0.04 magnitudes with a possible 13.25+-0.2 hour
single-peaked period. The seven new KBOs in the sample which show no
discernible variations within the uncertainties on short rotational time scales
are 2001 UQ18, (55565) 2002 AW197, (119979) 2002 WC19, (120132) 2003 FY128,
(136108) Eris 2003 UB313, (90482) Orcus 2004 DW, and (90568) 2004 GV9. The
three medium to large sized Kuiper Belt objects 2004 TY364, Orcus and 2004 GV9
show fairly steep linear phase curves (~0.18 to 0.26 mags per degree) between
phase angles of 0.1 and 1.5 degrees. The extremely large dwarf planet Eris
(2003 UB313) shows a shallower phase curve (0.09+-0.03 mags per degree) which
is more similar to the other known dwarf planet Pluto. It appears the surface
properties of the largest dwarf planets in the Kuiper Belt maybe different than
the smaller Kuiper Belt objects. This may have to do with the larger objects
ability to hold more volatile ices as well as sustain atmospheres. The absolute
magnitudes obtained using the measured phase slopes are a few tenths of
magnitudes different from those given by the MPC.
| astro-ph |
0704.1637 | Fischler-Susskind holographic cosmology revisited | When Fischler and Susskind proposed a holographic prescription based on the
Particle Horizon, they found that spatially closed cosmological models do not
verify it due to the apparently unavoidable recontraction of the Particle
Horizon area. In this article, after a short review of their original work, we
expose graphically and analytically that spatially closed cosmological models
can avoid this problem if they expand fast enough. It has been also shown that
the Holographic Principle is saturated for a codimension one brane dominated
Universe. The Fischler-Susskind prescription is used to obtain the maximum
number of degrees of freedom per Planck volume at the Planck era compatible
with the Holographic Principle.
| hep-th gr-qc |
0704.1638 | Accelerated expansion of the Universe filled up with the scalar
gravitons | The concept of the scalar graviton as the source of the dark matter and dark
energy of the gravitaional origin is applied to study the evolution of the
isotropic homogeneous Universe. A realistic self-consistent solution to the
modified pure gravity equations, which correctly describes the accelerated
expansion of the spatially flat Universe, is found and investigated. It is
argued that the scenario with the scalar gravitons filling up the Universe may
emulate the LCDM model, reducing thus the true dark matter to an artefact.
| gr-qc astro-ph hep-ph |
0704.1639 | Parity doubling in particle physics | Parity doubling in excited hadrons is reviewed. Parity degeneracy in hadrons
was first experimentally observed 40 years ago. Recently new experimental data
on light mesons caused much excitement and renewed interest to the phenomenon,
which still remains to be enigmatic. The present retrospective review is an
attempt to trace the history of parity doubling phenomenon, thus providing a
kind of introduction to the subject. We begin with early approaches of 1960s
(Regge theory and dynamical symmetries) and end up with the latest trends
(manifestations of broader degeneracies and AdS/QCD). We show the evolution of
various ideas about parity doubling. The experimental evidence for this
phenomenon is scrutinized in the non-strange sector. Some experiments of 1960s
devoted to the search for missing non-strange bosons are re-examined and it is
argued that results of these experiments are encouraging from the modern
perspective.
| hep-ph |
0704.1640 | Bergman kernels and equilibrium measures for ample line bundles | Let L be an ample holomorphic line bundle over a compact complex Hermitian
manifold X. Any fixed smooth Hermitian metric on L induces a Hilbert space
structure on the space of global holomorphic sections with values in the k:th
tensor power of L. In this paper various convergence results are obtained for
the corresponding Bergman kernels. The convergence is studied in the large k
limit and is expressed in terms of the equilibrium metric associated to the
fixed metric, as well as in terms of the Monge-Ampere measure of the fixed
metric itself on a certain support set. It is also shown that the equilibrium
metric has Lipschitz continuous first derivatives. These results can be seen as
generalizations of well-known results concerning the case when the curvature of
the fixed metric is positive (the corresponding equilibrium metric is then
simply the fixed metric itself).
| math.CV math.DG |
0704.1641 | U Geminorum: a test case for orbital parameters determination | High-resolution spectroscopy of U Gem was obtained during quiescence. We did
not find a hot spot or gas stream around the outer boundaries of the accretion
disk. Instead, we detected a strong narrow emission near the location of the
secondary star. We measured the radial velocity curve from the wings of the
double-peaked H$\alpha$ emission line, and obtained a semi-amplitude value that
is in excellent agreement with the obtained from observations in the
ultraviolet spectral region by Sion et al. (1998). We present also a new method
to obtain K_2, which enhances the detection of absorption or emission features
arising in the late-type companion. Our results are compared with published
values derived from the near-infrared NaI line doublet. From a comparison of
the TiO band with those of late type M stars, we find that a best fit is
obtained for a M6V star, contributing 5 percent of the total light at that
spectral region. Assuming that the radial velocity semi-amplitudes reflect
accurately the motion of the binary components, then from our results: K_em =
107+/-2 km/s; K_abs = 310+/-5 km/s, and using the inclination angle given by
Zhang & Robinson(1987); i = 69.7+/-0.7, the system parameters become: M_WD =
1.20+/-0.05 M_sun,; M_RD = 0.42+/-0.04 M_sun; and a = 1.55+/- 0.02 R_sun. Based
on the separation of the double emission peaks, we calculate an outer disk
radius of R_out/a ~0.61, close to the distance of the inner Lagrangian point
L_1/a~0.63. Therefore we suggest that, at the time of observations, the
accretion disk was filling the Roche-Lobe of the primary, and that the matter
leaving the L_1 point was colliding with the disc directly, producing the hot
spot at this location.
| astro-ph |
0704.1642 | Collective excitations of hard-core Bosons at half filling on square and
triangular lattices: Development of roton minima and collapse of roton gap | We study ground state properties and excitation spectra for hard-core Bosons
on square and triangular lattices, at half filling, using series expansion
methods. Nearest-neighbor repulsion between the Bosons leads to the development
of short-range density order at the antiferromagnetic wavevector, and
simultaneously a roton minima in the density excitation spectra. On the
square-lattice, the model maps on to the well studied XXZ model, and the roton
gap collapses to zero precisely at the Heisenberg symmetry point, leading to
the well known spectra for the Heisenberg antiferromagnet. On the
triangular-lattice, the collapse of the roton gap signals the onset of the
supersolid phase. Our results suggest that the transition from the superfluid
to the supersolid phase maybe weakly first order. We also find several features
in the density of states, including two-peaks and a sharp discontinuity, which
maybe observable in experimental realization of such systems.
| cond-mat.str-el |
0704.1643 | The LIL for $U$-statistics in Hilbert spaces | We give necessary and sufficient conditions for the (bounded) law of the
iterated logarithm for $U$-statistics in Hilbert spaces. As a tool we also
develop moment and tail estimates for canonical Hilbert-space valued
$U$-statistics of arbitrary order, which are of independent interest.
| math.PR |
0704.1644 | Circulating Current States in Bilayer Fermionic and Bosonic Systems | It is shown that fermionic polar molecules or atoms in a bilayer optical
lattice can undergo the transition to a state with circulating currents, which
spontaneously breaks the time reversal symmetry. Estimates of relevant
temperature scales are given and experimental signatures of the circulating
current phase are identified. Related phenomena in bosonic and spin systems
with ring exchange are discussed.
| cond-mat.other physics.atom-ph quant-ph |
0704.1645 | Non-Relativistic Propagators via Schwinger's Method | In order to popularize the so called Schwinger's method we reconsider the
Feynman propagator of two non-relativistic systems: a charged particle in a
uniform magnetic field and a charged harmonic oscillator in a uniform magnetic
field. Instead of solving the Heisenberg equations for the position and the
canonical momentum operators, ${\bf R}$ and ${\bf P}$, we apply this method by
solving the Heisenberg equations for the gauge invariant operators ${\bf R}$
and $\mathversion{bold}${\pi}$ = {\bf P}-e{\bf A}$, the latter being the
mechanical momentum operator. In our procedure we avoid fixing the gauge from
the beginning and the result thus obtained shows explicitly the gauge
dependence of the Feynman propagator.
| quant-ph hep-th |
0704.1646 | A linear RFQ ion trap for the Enriched Xenon Observatory | The design, construction, and performance of a linear radio-frequency ion
trap (RFQ) intended for use in the Enriched Xenon Observatory (EXO) are
described. EXO aims to detect the neutrinoless double-beta decay of $^{136}$Xe
to $^{136}$Ba. To suppress possible backgrounds EXO will complement the
measurement of decay energy and, to some extent, topology of candidate events
in a Xe filled detector with the identification of the daughter nucleus
($^{136}$Ba). The ion trap described here is capable of accepting, cooling, and
confining individual Ba ions extracted from the site of the candidate
double-beta decay event. A single trapped ion can then be identified, with a
large signal-to-noise ratio, via laser spectroscopy.
| physics.ins-det |
0704.1647 | How much entropy is produced in strongly coupled Quark-Gluon Plasma
(sQGP) by dissipative effects? | We argue that estimates of dissipative effects based on the first-order
hydrodynamics with shear viscosity are potentially misleading because higher
order terms in the gradient expansion of the dissipative part of the stress
tensor tend to reduce them. Using recently obtained sound dispersion relation
in thermal $\cal N$=4 supersymmetric plasma, we calculate the $resummed$ effect
of these high order terms for Bjorken expansion appropriate to RHIC/LHC
collisions. A reduction of entropy production is found to be substantial, up to
an order of magnitude.
| hep-ph |
0704.1648 | Spectral Analysis of the Chandra Comet Survey | We present results of the analysis of cometary X-ray spectra with an extended
version of our charge exchange emission model (Bodewits et al. 2006). We have
applied this model to the sample of 8 comets thus far observed with the Chandra
X-ray observatory and ACIS spectrometer in the 300-1000 eV range. The surveyed
comets are C/1999 S4 (LINEAR), C/1999 T1 (McNaught-Hartley), C/2000 WM1
(LINEAR), 153P/2002 (Ikeya-Zhang), 2P/2003 (Encke), C/2001 Q4 (NEAT), 9P/2005
(Tempel 1) and 73P/2006-B (Schwassmann-Wachmann 3) and the observations include
a broad variety of comets, solar wind environments and observational
conditions. The interaction model is based on state selective, velocity
dependent charge exchange cross sections and is used to explore how cometary
X-ray emission depend on cometary, observational and solar wind
characteristics. It is further demonstrated that cometary X-ray spectra mainly
reflect the state of the local solar wind. The current sample of Chandra
observations was fit using the constrains of the charge exchange model, and
relative solar wind abundances were derived from the X-ray spectra. Our
analysis showed that spectral differences can be ascribed to different solar
wind states, as such identifying comets interacting with (I) fast, cold wind,
(II), slow, warm wind and (III) disturbed, fast, hot winds associated with
interplanetary coronal mass ejections. We furthermore predict the existence of
a fourth spectral class, associated with the cool, fast high latitude wind.
| astro-ph |
0704.1649 | Hamiltonian formalism in a problem of 3-th waves hierarchy | By the method of discrete transformation equations of 3-th wave hierarchy are
constructed. We present in explicit form two Poisson structures, which allow to
construct Hamiltonian operator consequent application of which leads to all
equations of this hierarchy. For calculations it will be necessary results of
previous paper \cite{1}, which for convenience of the reader we present in
corresponding place of the text. The obtained formulae are checked by
independent calculations.
| hep-lat |
0704.1650 | Correlations, fluctuations and stability of a finite-size network of
coupled oscillators | The incoherent state of the Kuramoto model of coupled oscillators exhibits
marginal modes in mean field theory. We demonstrate that corrections due to
finite size effects render these modes stable in the subcritical case, i.e.
when the population is not synchronous. This demonstration is facilitated by
the construction of a non-equilibrium statistical field theoretic formulation
of a generic model of coupled oscillators. This theory is consistent with
previous results. In the all-to-all case, the fluctuations in this theory are
due completely to finite size corrections, which can be calculated in an
expansion in 1/N, where N is the number of oscillators. The N -> infinity limit
of this theory is what is traditionally called mean field theory for the
Kuramoto model.
| nlin.AO nlin.CD |
0704.1651 | Route to Lambda in conformally coupled phantom cosmology | In this letter we investigate acceleration in the flat cosmological model
with a conformally coupled phantom field and we show that acceleration is its
generic feature. We reduce the dynamics of the model to a 3-dimensional
dynamical system and analyze it on a invariant 2-dimensional submanifold. Then
the concordance FRW model with the cosmological constant $\Lambda$ is a global
attractor situated on a 2-dimensional invariant space. We also study the
behaviour near this attractor, which can be approximated by the dynamics of the
linearized part of the system. We demonstrate that trajectories of the
conformally coupled phantom scalar field with a simple quadratic potential
crosses the cosmological constant barrier infinitely many times in the phase
space. The universal behaviour of the scalar field and its potential is also
calculated. We conclude that the phantom scalar field conformally coupled to
gravity gives a natural dynamical mechanism of concentration of the equation of
state coefficient around the magical value $w_{\text{eff}}=-1$. We demonstrate
route to Lambda through the infinite times crossing the $w_{\text{eff}}=-1$
phantom divide.
| hep-th astro-ph |
0704.1652 | Interaction of Supernova Ejecta with Nearby Protoplanetary Disks | The early Solar System contained short-lived radionuclides such as 60Fe (t1/2
= 1.5 Myr) whose most likely source was a nearby supernova. Previous models of
Solar System formation considered a supernova shock that triggered the collapse
of the Sun's nascent molecular cloud. We advocate an alternative hypothesis,
that the Solar System's protoplanetary disk had already formed when a very
close (< 1 pc) supernova injected radioactive material directly into the disk.
We conduct the first numerical simulations designed to answer two questions
related to this hypothesis: will the disk be destroyed by such a close
supernova; and will any of the ejecta be mixed into the disk? Our simulations
demonstrate that the disk does not absorb enough momentum from the shock to
escape the protostar to which it is bound. Only low amounts (< 1%) of mass loss
occur, due to stripping by Kelvin-Helmholtz instabilities across the top of the
disk, which also mix into the disk about 1% of the intercepted ejecta. These
low efficiencies of destruction and injectation are due to the fact that the
high disk pressures prevent the ejecta from penetrating far into the disk
before stalling. Injection of gas-phase ejecta is too inefficient to be
consistent with the abundances of radionuclides inferred from meteorites. On
the other hand, the radionuclides found in meteorites would have condensed into
dust grains in the supernova ejecta, and we argue that such grains will be
injected directly into the disk with nearly 100% efficiency. The meteoritic
abundances of the short-lived radionuclides such as 60Fe therefore are
consistent with injection of grains condensed from the ejecta of a nearby (< 1
pc) supernova, into an already-formed protoplanetary disk.
| astro-ph |
0704.1653 | Scaling cosmologies, geodesic motion and pseudo-susy | One-parameter solutions in supergravity carried by scalars and a metric trace
out curves on the scalar manifold. In ungauged supergravity these curves
describe a geodesic motion. It is known that a geodesic motion sometimes occurs
in the presence of a scalar potential and for time-dependent solutions this can
happen for scaling cosmologies. This note contains a further study of such
solutions in the context of pseudo-supersymmetry for multi-field systems whose
first-order equations we derive using a Bogomol'nyi-like method. In particular
we show that scaling solutions that are pseudo-BPS must describe geodesic
curves. Furthermore, we clarify how to solve the geodesic equations of motion
when the scalar manifold is a maximally non-compact coset such as occurs in
maximal supergravity. This relies upon a parametrization of the coset in the
Borel gauge. We then illustrate this with the cosmological solutions of
higher-dimensional gravity compactified on a $n$-torus.
| hep-th astro-ph |
0704.1654 | The Peculiar Velocities of Local Type Ia Supernovae and their Impact on
Cosmology | We quantify the effect of supernova Type Ia peculiar velocities on the
derivation of cosmological parameters. The published distant and local Ia SNe
used for the Supernova Legacy Survey first-year cosmology report form the
sample for this study. While previous work has assumed that the local SNe are
at rest in the CMB frame (the No Flow assumption), we test this assumption by
applying peculiar velocity corrections to the local SNe using three different
flow models. The models are based on the IRAS PSCz galaxy redshift survey, have
varying beta = Omega_m^0.6/b, and reproduce the Local Group motion in the CMB
frame. These datasets are then fit for w, Omega_m, and Omega_Lambda using
flatness or LambdaCDM and a BAO prior. The chi^2 statistic is used to examine
the effect of the velocity corrections on the quality of the fits. The most
favored model is the beta=0.5 model, which produces a fit significantly better
than the No Flow assumption, consistent with previous peculiar velocity
studies. By comparing the No Flow assumption with the favored models we derive
the largest potential systematic error in w caused by ignoring peculiar
velocities to be Delta w = +0.04. For Omega_Lambda, the potential error is
Delta Omega_Lambda = -0.04 and for Omega_m, the potential error is Delta
Omega_m < +0.01. The favored flow model (beta=0.5) produces the following
cosmological parameters: w = -1.08 (+0.09,-0.08), Omega_m = 0.27 (+0.02,-0.02)
assuming a flat cosmology, and Omega_Lambda = 0.80 (+0.08,-0.07) and Omega_m =
0.27 (+0.02,-0.02) for a w = -1 (LambdaCDM) cosmology.
| astro-ph |
0704.1655 | Creation of Quark-gluon Plasma in Celestial Laboratories | It is shown that a gravitationally collapsing black hole acts as an ultrahigh
energy particle accelerator that can accelerate particles to energies
inconceivable in any terrestrial particle accelerator, and that when the energy
E of the particles comprising the matter in the black hole is $ \sim 10^{2} $
GeV or more,or equivalently the temperature T is $ \sim 10^{15}$ K or more, the
entire matter in the black hole will be in the form of quark-gluon plasma
permeated by leptons.
| physics.gen-ph |
0704.1656 | Temperature-driven transition from the Wigner Crystal to the
Bond-Charge-Density Wave in the Quasi-One-Dimensional Quarter-Filled band | It is known that within the interacting electron model Hamiltonian for the
one-dimensional 1/4-filled band, the singlet ground state is a Wigner crystal
only if the nearest neighbor electron-electron repulsion is larger than a
critical value. We show that this critical nearest neighbor Coulomb interaction
is different for each spin subspace, with the critical value decreasing with
increasing spin. As a consequence, with the lowering of temperature, there can
occur a transition from a Wigner crystal charge-ordered state to a spin-Peierls
state that is a Bond-Charge-Density Wave with charge occupancies different from
the Wigner crystal. This transition is possible because spin excitations from
the spin-Peierls state in the 1/4-filled band are necessarily accompanied by
changes in site charge densities. We apply our theory to the 1/4-filled band
quasi-one-dimensional organic charge-transfer solids in general and to 2:1
tetramethyltetrathiafulvalene (TMTTF) and tetramethyltetraselenafulvalene
(TMTSF) cationic salts in particular. We believe that many recent experiments
strongly indicate the Wigner crystal to Bond-Charge-Density Wave transition in
several members of the TMTTF family. We explain the occurrence of two different
antiferromagnetic phases but a single spin-Peierls state in the generic phase
diagram for the 2:1 cationic solids. The antiferromagnetic phases can have
either the Wigner crystal or the Bond-Charge-Spin-Density Wave charge
occupancies. The spin-Peierls state is always a Bond-Charge-Density Wave.
| cond-mat.str-el |
0704.1657 | Bubbling Surface Operators And S-Duality | We construct smooth asymptotically AdS_5xS^5 solutions of Type IIB
supergravity corresponding to all the half-BPS surface operators in N=4 SYM.
All the parameters labeling a half-BPS surface operator are identified in the
corresponding bubbling geometry. We use the supergravity description of surface
operators to study the action of the SL(2,Z) duality group of N=4 SYM on the
parameters of the surface operator, and find that it coincides with the recent
proposal by Gukov and Witten in the framework of the gauge theory approach to
the geometrical Langlands with ramification. We also show that whenever a
bubbling geometry becomes singular that the path integral description of the
corresponding surface operator also becomes singular.
| hep-th |
0704.1658 | Resolving Cosmic Gamma Ray Anomalies with Dark Matter Decaying Now | Dark matter particles need not be completely stable, and in fact they may be
decaying now. We consider this possibility in the frameworks of universal extra
dimensions and supersymmetry with very late decays of WIMPs to Kaluza-Klein
gravitons and gravitinos. The diffuse photon background is a sensitive probe,
even for lifetimes far greater than the age of the Universe. Remarkably, both
the energy spectrum and flux of the observed MeV gamma ray excess may be
naturally explained by decaying dark matter with MeV mass splittings. Future
observations of continuum and line photon fluxes will test this explanation and
may provide novel constraints on cosmological parameters.
| astro-ph hep-ph |
0704.1659 | Neutrino-cooled accretion and GRB variability | For accretion rates Mdot~0.1 Msun/s to a few solar mass black hole the inner
part of the disk is expected to make a transition from advection dominance to
neutrino cooling. This transition is characterized by sharp changes of the disk
properties. I argue here that during this transition, a modest increase of the
accretion rate leads to powerful enhancement of the Poynting luminosity of the
GRB flow and decrease of its baryon loading. These changes of the
characteristics of the GRB flow translate into changing gamma-ray spectra from
the photosphere of the flow. The photospheric interpretation of the GRB
emission explains the observed narrowing of GRB pulses with increasing photon
energy and the luminosity-spectral peak relation within and among bursts.
| astro-ph |
0704.1660 | The VVDS type-1 AGN sample: The faint end of the luminosity function | In a previous paper (Gavignaud et al. 2006), we presented the type-1 Active
Galactic Nuclei (AGN) sample obtained from the first epoch data of the
VIMOS-VLT Deep Survey (VVDS). The sample consists of 130 faint, broad-line AGN
with redshift up to z=5 and 17.5< I <24.0, selected on the basis of their
spectra. In this paper we present the measurement of the Optical Luminosity
Function up to z=3.6 derived from this sample, we compare our results with
previous results from brighter samples both at low and at high redshift. Our
data, more than one magnitude fainter than previous optical surveys, allow us
to constrain the faint part of the luminosity function up to high redshift. By
combining our faint VVDS sample with the large sample of bright AGN extracted
from the SDSS DR3 (Richards et al., 2006b) and testing a number of different
evolutionary models, we find that the model which better represents the
combined luminosity functions, over a wide range of redshift and luminosity, is
a luminosity dependent density evolution (LDDE) model, similar to those derived
from the major X-surveys. Such a parameterization allows the redshift of the
AGN space density peak to change as a function of luminosity and explains the
excess of faint AGN that we find at 1.0< z <1.5. On the basis of this model we
find, for the first time from the analysis of optically selected samples, that
the peak of the AGN space density shifts significantly towards lower redshift
going to lower luminosity objects. This result, already found in a number of
X-ray selected samples of AGN, is consistent with a scenario of "AGN cosmic
downsizing", in which the density of more luminous AGN, possibly associated to
more massive black holes, peaks earlier in the history of the Universe, than
that of low luminosity ones.
| astro-ph |
0704.1661 | Can a Black Hole Collapse to a Space-time Singularity? | A critique of the singularity theorems of Penrose, Hawking, and Geroch is
given. It is pointed out that a gravitationally collapsing black hole acts as
an ultrahigh energy particle accelerator that can accelerate particles to
energies inconceivable in any terrestrial particle accelerator, and that when
the energy $E$ of the particles comprising matter in a black hole is $\sim
10^{2} GeV$ or more, or equivalently, the temperature $T$ is $\sim 10^{15} K$
or more, the entire matter in the black hole is converted into quark-gluon
plasma permeated by leptons. As quarks and leptons are fermions, it is
emphasized that the collapse of a black-hole to a space-time singularity is
inhibited by Pauli's exclusion principle. It is also suggested that ultimately
a black hole may end up either as a stable quark star, or as a pulsating quark
star which may be a source of gravitational radiation, or it may simply explode
with a mini bang of a sort.
| physics.gen-ph |
0704.1662 | Right-Handed Quark Mixings in Minimal Left-Right Symmetric Model with
General CP Violation | We present a systematic approach to solve analytically for the right-handed
quark mixings in the minimal left-right symmetric model which generally has
both explicit and spontaneous CP violations. The leading-order result has the
same hierarchical structure as the left-handed CKM mixing, but with additional
CP phases originating from a spontaneous CP-violating phase in the Higgs vev.
We explore the phenomenology entailed by the new right-handed mixing matrix,
particularly the bounds on the mass of $W_R$ and the CP phase of the Higgs vev.
| hep-ph |
0704.1663 | Dynamics of single polymers under extreme confinement | We study the dynamics of a single chain polymer confined to a two dimensional
cell. We introduce a kinetically constrained lattice gas model that preserves
the connectivity of the chain, and we use this kinetically constrained model to
study the dynamics of the polymer at varying densities through Monte Carlo
simulations. Even at densities close to the fully-packed configuration, we find
that the monomers comprising the chain manage to diffuse around the box with a
root mean square displacement of the order of the box dimensions over time
scales for which the overall geometry of the polymer is, nevertheless, largely
preserved. To capture this shape persistence, we define the local tangent field
and study the two-time tangent-tangent correlation function, which exhibits a
glass-like behavior. In both closed and open chains, we observe reptational
motion and reshaping through local fingering events which entail global monomer
displacement.
| cond-mat.stat-mech cond-mat.soft |
0704.1664 | Diffuse Optical Light in Galaxy Clusters II: Correlations with Cluster
Properties | We have measured the flux, profile, color, and substructure in the diffuse
intracluster light (ICL) in a sample of ten galaxy clusters with a range of
mass, morphology, redshift, and density. Deep, wide-field observations for this
project were made in two bands at the one meter Swope and 2.5 meter du Pont
telescope at Las Campanas Observatory. Careful attention in reduction and
analysis was paid to the illumination correction, background subtraction, point
spread function determination, and galaxy subtraction. ICL flux is detected in
both bands in all ten clusters ranging from 7.6 x 10^{10} to 7.0 x 10^{11}
h^{-1} solar luminosities in r and 1.4 x 10^{10} to 1.2 x 10^{11} h^{-1} solar
luminosities in the B-band. These fluxes account for 6 to 22% of the total
cluster light within one quarter of the virial radius in r and 4 to 21% in the
B-band. Average ICL B-r colors range from 1.5 to 2.8 mags when k and evolution
corrected to the present epoch. In several clusters we also detect ICL in group
environments near the cluster center and up to ~1 h^{-1} Mpc distant from the
cluster center. Our sample, having been selected from the Abell sample, is
incomplete in that it does not include high redshift clusters with low density,
low flux, or low mass, and it does not include low redshift clusters with high
flux, mass, or density. This bias makes it difficult to interpret correlations
between ICL flux and cluster properties. Despite this selection bias, we do
find that the presence of a cD galaxy corresponds to both centrally
concentrated galaxy profiles and centrally concentrated ICL profiles. This is
consistent with ICL either forming from galaxy interactions at the center, or
forming at earlier times in groups and later combining in the center.
| astro-ph |
0704.1665 | Approach to Physical Reality: a note on Poincare Group and the
philosophy of Nagarjuna | We argue about a possible scenario of physical reality based on the
parallelism between Poincare group and the sunyata philosophy of Nagarjuna. The
notion of "relational" is the common denominator of two views. We have
approached the relational concept in third-person perspective (ontic level). It
is possible to deduce different physical consequence and interpretation through
first-person perspective approach. This relational interpretation leave open
the questions: i)we must abandon the idea for a physical system the possibility
to extract completeness information? ii)we must abandon the idea to infer a
possible structure of physical reality?
| physics.gen-ph |
0704.1666 | Ultraviolet Observations of Supernovae | The motivations to make ultraviolet (UV) studies of supernovae (SNe) are
reviewed and discussed in the light of the results obtained so far by means of
IUE and HST observations. It appears that UV studies of SNe can, and do lead to
fundamental results not only for our understanding of the SN phenomenon, such
as the kinematics and the metallicity of the ejecta, but also for exciting new
findings in Cosmology, such as the tantalizing evidence for "dark energy" that
seems to pervade the Universe and to dominate its energetics. The need for
additional and more detailed UV observations is also considered and discussed.
| astro-ph |
0704.1667 | Stochastic fluctuations in metabolic pathways | Fluctuations in the abundance of molecules in the living cell may affect its
growth and well being. For regulatory molecules (e.g., signaling proteins or
transcription factors), fluctuations in their expression can affect the levels
of downstream targets in a network. Here, we develop an analytic framework to
investigate the phenomenon of noise correlation in molecular networks.
Specifically, we focus on the metabolic network, which is highly inter-linked,
and noise properties may constrain its structure and function. Motivated by the
analogy between the dynamics of a linear metabolic pathway and that of the
exactly soluable linear queueing network or, alternatively, a mass transfer
system, we derive a plethora of results concerning fluctuations in the
abundance of intermediate metabolites in various common motifs of the metabolic
network. For all but one case examined, we find the steady-state fluctuation in
different nodes of the pathways to be effectively uncorrelated. Consequently,
fluctuations in enzyme levels only affect local properties and do not propagate
elsewhere into metabolic networks, and intermediate metabolites can be freely
shared by different reactions. Our approach may be applicable to study
metabolic networks with more complex topologies, or protein signaling networks
which are governed by similar biochemical reactions. Possible implications for
bioinformatic analysis of metabolimic data are discussed.
| q-bio.MN cond-mat.stat-mech |
0704.1668 | A new search for planet transits in NGC 6791 | Context. Searching for planets in open clusters allows us to study the
effects of dynamical environment on planet formation and evolution.
Aims. Considering the strong dependence of planet frequency on stellar
metallicity, we studied the metal rich old open cluster NGC 6791 and searched
for close-in planets using the transit technique.
Methods. A ten-night observational campaign was performed using the
Canada-France-Hawaii Telescope (3.6m), the San Pedro M\'artir telescope (2.1m),
and the Loiano telescope (1.5m). To increase the transit detection probability
we also made use of the Bruntt et al. (2003) eight-nights observational
campaign. Adequate photometric precision for the detection of planetary
transits was achieved.
Results. Should the frequency and properties of close-in planets in NGC 6791
be similar to those orbiting field stars of similar metallicity, then detailed
simulations foresee the presence of 2-3 transiting planets. Instead, we do not
confirm the transit candidates proposed by Bruntt et al. (2003). The
probability that the null detection is simply due to chance coincidence is
estimated to be 3%-10%, depending on the metallicity assumed for the cluster.
Conclusions. Possible explanations of the null-detection of transits include:
(i) a lower frequency of close-in planets in star clusters; (ii) a smaller
planetary radius for planets orbiting super metal rich stars; or (iii)
limitations in the basic assumptions. More extensive photometry with 3-4m class
telescopes is required to allow conclusive inferences about the frequency of
planets in NGC 6791.
| astro-ph |
0704.1669 | Possible polarisation and spin dependent aspects of quantum gravity | We argue that quantum gravity theories that carry a Lie algebraic
modification of the Poincare' and Heisenberg algebras inevitably provide
inhomogeneities that may serve as seeds for cosmological structure formation.
Furthermore, in this class of theories one must expect a strong polarisation
and spin dependence of various quantum-gravity effects.
| gr-qc astro-ph hep-ph |
0704.1670 | On the support genus of a contact structure | The algorithm given by Akbulut-Ozbagci constructs an explicit open book
decomposition on a contact three-manifold described by a contact surgery on a
link in the three-sphere. In this article, we will improve this algorithm by
using Giroux's contact cell decomposition process. Our algorithm is more
economical on choosing the supporting genus of the open book; in particular it
gives a good upper bound for the recently defined ``minimal supporting genus
invariant'' of contact structures.
| math.GT math.SG |
0704.1671 | Very Massive Stars in High-Redshift Galaxies | A significant fraction of Lyman Alpha (Lya) emitting galaxies (LAEs) at z>
5.7 have rest-frame equivalent widths (EW) greater than ~100 Angstrom. However
only a small fraction of the Lya flux produced by a galaxy is transmitted
through the IGM, which implies intrinsic Lya EWs that are in excess of the
maximum allowed for a population-II stellar population having a Salpeter mass
function. In this paper we study characteristics of the sources powering Lya
emission in high redshift galaxies. We propose a simple model for Lya emitters
in which galaxies undergo a burst of very massive star formation that results
in a large intrinsic EW, followed by a phase of population-II star formation
with a lower EW. We confront this model with a range of high redshift
observations and find that the model is able to simultaneously describe the
following eight properties of the high redshift galaxy population with
plausible values for parameters like the efficiency and duration of star
formation: i-iv) the UV and Lya luminosity functions of LAEs at z=5.7 and 6.5,
v-vi) the mean and variance of the EW distribution of Lya selected galaxies at
z=5.7, vii) the EW distribution of i-drop galaxies at z~6, and viii) the
observed correlation of stellar age with EW. Our modeling suggests that the
observed anomalously large intrinsic equivalent widths require a burst of very
massive star formation lasting no more than a few to ten percent of the
galaxies star forming lifetime. This very massive star formation may indicate
the presence of population-III star formation in a few per cent of i-drop
galaxies, and in about half of the Lya selected galaxies.
| astro-ph |
0704.1672 | Two center multipole expansion method: application to macromolecular
systems | We propose a new theoretical method for the calculation of the interaction
energy between macromolecular systems at large distances. The method provides a
linear scaling of the computing time with the system size and is considered as
an alternative to the well known fast multipole method. Its efficiency,
accuracy and applicability to macromolecular systems is analyzed and discussed
in detail.
| physics.bio-ph physics.comp-ph |
0704.1673 | Holographic formula for Q-curvature | This paper derives an explicit formula for Branson's Q-curvature in
even-dimensional conformal geometry. The ingredients in the formula come from
the Poincare metric in one higher dimension; hence the formula is called
holographic. When specialized to the conformally flat case, the holographic
formula expresses Q-curvature as a multiple of the Pfaffian and the divergence
of a natural one-form. The paper also outlines the relation between holographic
formulae for Q-curvature and a new theory of conformally covariant families of
differential operators due to the second author.
| math.DG |
0704.1674 | The azimuth structure of nuclear collisions -- I | We describe azimuth structure commonly associated with elliptic and directed
flow in the context of 2D angular autocorrelations for the purpose of precise
separation of so-called nonflow (mainly minijets) from flow. We extend the
Fourier-transform description of azimuth structure to include power spectra and
autocorrelations related by the Wiener-Khintchine theorem. We analyze several
examples of conventional flow analysis in that context and question the
relevance of reaction plane estimation to flow analysis. We introduce the 2D
angular autocorrelation with examples from data analysis and describe a
simulation exercise which demonstrates precise separation of flow and nonflow
using the 2D autocorrelation method. We show that an alternative correlation
measure based on Pearson's normalized covariance provides a more intuitive
measure of azimuth structure.
| hep-ph |
0704.1675 | Exploiting Social Annotation for Automatic Resource Discovery | Information integration applications, such as mediators or mashups, that
require access to information resources currently rely on users manually
discovering and integrating them in the application. Manual resource discovery
is a slow process, requiring the user to sift through results obtained via
keyword-based search. Although search methods have advanced to include evidence
from document contents, its metadata and the contents and link structure of the
referring pages, they still do not adequately cover information sources --
often called ``the hidden Web''-- that dynamically generate documents in
response to a query. The recently popular social bookmarking sites, which allow
users to annotate and share metadata about various information sources, provide
rich evidence for resource discovery. In this paper, we describe a
probabilistic model of the user annotation process in a social bookmarking
system del.icio.us. We then use the model to automatically find resources
relevant to a particular information domain. Our experimental results on data
obtained from \emph{del.icio.us} show this approach as a promising method for
helping automate the resource discovery task.
| cs.AI cs.CY cs.DL |
0704.1676 | Personalizing Image Search Results on Flickr | The social media site Flickr allows users to upload their photos, annotate
them with tags, submit them to groups, and also to form social networks by
adding other users as contacts. Flickr offers multiple ways of browsing or
searching it. One option is tag search, which returns all images tagged with a
specific keyword. If the keyword is ambiguous, e.g., ``beetle'' could mean an
insect or a car, tag search results will include many images that are not
relevant to the sense the user had in mind when executing the query. We claim
that users express their photography interests through the metadata they add in
the form of contacts and image annotations. We show how to exploit this
metadata to personalize search results for the user, thereby improving search
performance. First, we show that we can significantly improve search precision
by filtering tag search results by user's contacts or a larger social network
that includes those contact's contacts. Secondly, we describe a probabilistic
model that takes advantage of tag information to discover latent topics
contained in the search results. The users' interests can similarly be
described by the tags they used for annotating their images. The latent topics
found by the model are then used to personalize search results by finding
images on topics that are of interest to the user.
| cs.IR cs.AI cs.CY cs.DL cs.HC |
0704.1677 | Resummed Cross Section for Jet Production at Hadron Colliders | We study the resummation of large logarithmic perturbative corrections to the
single-inclusive jet cross section at hadron colliders. The corrections we
address arise near the threshold for the partonic reaction, when the incoming
partons have just enough energy to produce the high-transverse-momentum final
state. The structure of the resulting logarithmic corrections is known to
depend crucially on the treatment of the invariant mass of the produced jet at
threshold. We allow the jet to have a non-vanishing mass at threshold, which
most closely corresponds to the situation in experiment. Matching our results
to available semi-analytical next-to-leading-order calculations, we derive
resummed results valid to next-to-leading logarithmic accuracy. We present
numerical results for the resummation effects at Tevatron and RHIC energies.
| hep-ph |
0704.1678 | Settling the Complexity of Computing Two-Player Nash Equilibria | We settle a long-standing open question in algorithmic game theory. We prove
that Bimatrix, the problem of finding a Nash equilibrium in a two-player game,
is complete for the complexity class PPAD Polynomial Parity Argument, Directed
version) introduced by Papadimitriou in 1991.
This is the first of a series of results concerning the complexity of Nash
equilibria. In particular, we prove the following theorems:
Bimatrix does not have a fully polynomial-time approximation scheme unless
every problem in PPAD is solvable in polynomial time. The smoothed complexity
of the classic Lemke-Howson algorithm and, in fact, of any algorithm for
Bimatrix is not polynomial unless every problem in PPAD is solvable in
randomized polynomial time. Our results demonstrate that, even in the simplest
form of non-cooperative games, equilibrium computation and approximation are
polynomial-time equivalent to fixed point computation. Our results also have
two broad complexity implications in mathematical economics and operations
research: Arrow-Debreu market equilibria are PPAD-hard to compute. The P-Matrix
Linear Complementary Problem is computationally harder than convex programming
unless every problem in PPAD is solvable in polynomial time.
| cs.GT cs.CC |
0704.1679 | Equation of State in Relativistic Magnetohydrodynamics: variable versus
constant adiabatic index | The role of the equation of state for a perfectly conducting, relativistic
magnetized fluid is the main subject of this work. The ideal constant
$\Gamma$-law equation of state, commonly adopted in a wide range of
astrophysical applications, is compared with a more realistic equation of state
that better approximates the single-specie relativistic gas. The paper focus on
three different topics. First, the influence of a more realistic equation of
state on the propagation of fast magneto-sonic shocks is investigated. This
calls into question the validity of the constant $\Gamma$-law equation of state
in problems where the temperature of the gas substantially changes across
hydromagnetic waves. Second, we present a new inversion scheme to recover
primitive variables (such as rest-mass density and pressure) from conservative
ones that allows for a general equation of state and avoids catastrophic
numerical cancellations in the non-relativistic and ultrarelativistic limits.
Finally, selected numerical tests of astrophysical relevance (including
magnetized accretion flows around Kerr black holes) are compared using
different equations of state. Our main conclusion is that the choice of a
realistic equation of state can considerably bear upon the solution when
transitions from cold to hot gas (or viceversa) are present. Under these
circumstances, a polytropic equation of state can significantly endanger the
solution.
| astro-ph |
0704.1680 | Carbon Nanotube Thin Film Field Emitting Diode: Understanding the System
Response Based on Multiphysics Modeling | In this paper, we model the evolution and self-assembly of randomly oriented
carbon nanotubes (CNTs), grown on a metallic substrate in the form of a thin
film for field emission under diode configuration. Despite high output, the
current in such a thin film device often decays drastically. The present paper
is focused on understanding this problem. A systematic, multiphysics based
modelling approach is proposed. First, a nucleation coupled model for
degradation of the CNT thin film is derived, where the CNTs are assumed to
decay by fragmentation and formation of clusters. The random orientation of the
CNTs and the electromechanical interaction are then modeled to explain the
self-assembly. The degraded state of the CNTs and the electromechanical force
are employed to update the orientation of the CNTs. Field emission current at
the device scale is finally obtained by using the Fowler-Nordheim equation and
integration over the computational cell surfaces on the anode side. The
simulated results are in close agreement with the experimental results. Based
on the developed model, numerical simulations aimed at understanding the
effects of various geometric parameters and their statistical features on the
device current history are reported.
| cond-mat.mtrl-sci cond-mat.mes-hall |
0704.1681 | Demographics of Transition Objects | The unusual properties of transition objects (young stars with an optically
thin inner disc surrounded by an optically thick outer disc) suggest that
significant disc evolution has occured in these systems. We explore the nature
of these systems by examining their demographics, specifically their stellar
accretion rates (Mdot) and disc masses (Mdisc) compared to those of accreting T
Tauri stars of comparable age. We find that transition objects in Taurus occupy
a restricted region of the Mdot vs. Mdisc plane. Compared to non-transition
single stars in Taurus, they have stellar accretion rates that are typically
~10 times lower at the same disc mass and median disc masses ~4 times larger.
These properties are anticipated by several proposed planet formation theories
and suggest that the formation of Jovian mass planets may play a significant
role in explaining the origin of at least some transition objects. Considering
transition objects as a distinct demographic group among accreting T Tauri
stars leads to a tighter relationship between disc masses and stellar accretion
rates, with a slope between the two quantities that is close to the value of
unity expected in simple theories of disc accretion.
| astro-ph |
0704.1682 | Modeling the Field Emission Current Fluctuation in Carbon Nanotube Thin
Films | Owing to their distinct properties, carbon nanotubes (CNTs) have emerged as
promising candidate for field emission devices. It has been found
experimentally that the results related to the field emission performance show
variability. The design of an efficient field emitting device requires the
analysis of the variabilities with a systematic and multiphysics based modeling
approach. In this paper, we develop a model of randomly oriented CNTs in a thin
film by coupling the field emission phenomena, the electron-phonon transport
and the mechanics of single isolated CNT. A computational scheme is developed
by which the states of CNTs are updated in time incremental manner. The device
current is calculated by using Fowler-Nordheim equation for field emission to
study the performance at the device scale.
| cond-mat.mtrl-sci cond-mat.mes-hall |
0704.1683 | Spectral averaging for trace compatible operators | In this note the notions of trace compatible operators and infinitesimal
spectral flow are introduced. We define the spectral shift function as the
integral of infinitesimal spectral flow. It is proved that the spectral shift
function thus defined is absolutely continuous and Krein's formula is
established. Some examples of trace compatible affine spaces of operators are
given.
| math.FA math.SP |
0704.1684 | The molecular environment of massive star forming cores associated with
Class II methanol maser emission | Methanol maser emission has proven to be an excellent signpost of regions
undergoing massive star formation (MSF). To investigate their role as an
evolutionary tracer, we have recently completed a large observing program with
the ATCA to derive the dynamical and physical properties of molecular/ionised
gas towards a sample of MSF regions traced by 6.7 GHz methanol maser emission.
We find that the molecular gas in many of these regions breaks up into multiple
sub-clumps which we separate into groups based on their association
with/without methanol maser and cm continuum emission. The temperature and
dynamic state of the molecular gas is markedly different between the groups.
Based on these differences, we attempt to assess the evolutionary state of the
cores in the groups and thus investigate the role of class II methanol masers
as a tracer of MSF.
| astro-ph |
0704.1685 | Gravitating Global k-monopole | A gravitating global k-monopole produces a tiny gravitational field outside
the core in addition to a solid angular deficit in the k-field theory. As a new
feature, the gravitational field can be attractive or repulsive depending on
the non-canonical kinetic term.
| gr-qc |
0704.1686 | Effect of atomic beam alignment on photon correlation measurements in
cavity QED | Quantum trajectory simulations of a cavity QED system comprising an atomic
beam traversing a standing-wave cavity are carried out. The delayed photon
coincident rate for forwards scattering is computed and compared with the
measurements of Rempe et al. [Phys. Rev. Lett. 67, 1727 (1991)] and Foster et
al. [Phys. Rev. A 61, 053821 (2000)]. It is shown that a moderate atomic beam
misalignment can account for the degradation of the predicted correlation. Fits
to the experimental data are made in the weak-field limit with a single
adjustable parameter--the atomic beam tilt from perpendicular to the cavity
axis. Departures of the measurement conditions from the weak-field limit are
discussed.
| quant-ph |
0704.1687 | Studies on optimizing potential energy functions for maximal intrinsic
hyperpolarizability | We use numerical optimization to study the properties of (1) the class of
one-dimensional potential energy functions and (2) systems of point charges in
two-dimensions that yield the largest hyperpolarizabilities, which we find to
be within 30% of the fundamental limit. We investigate the character of the
potential energy functions and resulting wavefunctions and find that a broad
range of potentials yield the same intrinsic hyperpolarizability ceiling of
0.709.
| physics.optics physics.chem-ph |
0704.1688 | Critical test for Altshuler-Aronov theory: Evolution of the density of
states singularity in double perovskite Sr$_2$FeMoO$_6$ with controlled
disorder | With high-resolution photoemission spectroscopy measurements, the density of
states (DOS) near the Fermi level ($E_\mathrm{F}$) of double perovskite
Sr$_2$FeMoO$_6$ having different degrees of Fe/Mo antisite disorder has been
investigated with varying temperature. The DOS near $E_\mathrm{F}$ showed a
systematic depletion with increasing degree of disorder, and recovered with
increasing temperature. Altshuler-Aronov (AA) theory of disordered metals well
explains the dependences of the experimental results. Scaling analysis of the
spectra provides experimental indication for the functional form of the AA DOS
singularity.
| cond-mat.mtrl-sci cond-mat.str-el |
0704.1689 | Some Properties of and Open Problems on Hessian Nilpotent Polynomials | In the recent progress [BE1], [M], [Z1] and [Z2], the well-known Jacobian
conjecture ([BCW], [E]) has been reduced to a problem on HN (Hessian nilpotent)
polynomials (the polynomials whose Hessian matrix are nilpotent) and their
(deformed) inversion pairs. In this paper, we prove several results on HN
polynomials, their (deformed) inversion pairs as well as the associated
symmetric polynomial or formal maps. We also propose some open problems for
further study of these objects.
| math.CV math.AG |
0704.1690 | Two Results on Homogeneous Hessian Nilpotent Polynomials | Let $z=(z_1, ..., z_n)$ and $\Delta=\sum_{i=1}^n \frac {\partial^2}{\partial
z^2_i}$ the Laplace operator. A formal power series $P(z)$ is said to be {\it
Hessian Nilpotent}(HN) if its Hessian matrix $\Hes P(z)=(\frac {\partial^2
P}{\partial z_i\partial z_j})$ is nilpotent. In recent developments in [BE1],
[M] and [Z], the Jacobian conjecture has been reduced to the following
so-called {\it vanishing conjecture}(VC) of HN polynomials: {\it for any
homogeneous HN polynomial $P(z)$ $($of degree $d=4$$)$, we have $\Delta^m
P^{m+1}(z)=0$ for any $m>>0$.} In this paper, we first show that, the VC holds
for any homogeneous HN polynomial $P(z)$ provided that the projective
subvarieties ${\mathcal Z}_P$ and ${\mathcal Z}_{\sigma_2}$ of $\mathbb C
P^{n-1}$ determined by the principal ideals generated by $P(z)$ and
$\sigma_2(z):=\sum_{i=1}^n z_i^2$, respectively, intersect only at regular
points of ${\mathcal Z}_P$. Consequently, the Jacobian conjecture holds for the
symmetric polynomial maps $F=z-\nabla P$ with $P(z)$ HN if $F$ has no non-zero
fixed point $w\in \mathbb C^n$ with $\sum_{i=1}^n w_i^2=0$. Secondly, we show
that the VC holds for a HN formal power series $P(z)$ if and only if, for any
polynomial $f(z)$, $\Delta^m (f(z)P(z)^m)=0$ when $m>>0$.
| math.AG math.CV |
0704.1691 | A Vanishing Conjecture on Differential Operators with Constant
Coefficients | In the recent progress [BE1], [Me] and [Z2], the well-known JC (Jacobian
conjecture) ([BCW], [E]) has been reduced to a VC (vanishing conjecture) on the
Laplace operators and HN (Hessian nilpotent) polynomials (the polynomials whose
Hessian matrix are nilpotent). In this paper, we first show that the vanishing
conjecture above, hence also the JC, is equivalent to a vanishing conjecture
for all 2nd order homogeneous differential operators $\Lambda$ and
$\Lambda$-nilpotent polynomials $P$ (the polynomials $P(z)$ satisfying
$\Lambda^m P^m=0$ for all $m\ge 1$). We then transform some results in the
literature on the JC, HN polynomials and the VC of the Laplace operators to
certain results on $\Lambda$-nilpotent polynomials and the associated VC for
2nd order homogeneous differential operators $\Lambda$. This part of the paper
can also be read as a short survey on HN polynomials and the associated VC in
the more general setting. Finally, we discuss a still-to-be-understood
connection of $\Lambda$-nilpotent polynomials in general with the classical
orthogonal polynomials in one or more variables. This connection provides a
conceptual understanding for the isotropic properties of homogeneous
$\Lambda$-nilpotent polynomials for the 2nd order homogeneous full rank
differential operators $\Lambda$ with constant coefficients.
| math.CV math.AG |
0704.1692 | Effects of accelerating growth on the evolution of weighted complex
networks | Many real systems possess accelerating statistics where the total number of
edges grows faster than the network size. In this paper, we propose a simple
weighted network model with accelerating growth. We derive analytical
expressions for the evolutions and distributions for strength, degree, and
weight, which are relevant to accelerating growth. We also find that
accelerating growth determines the clustering coefficient of the networks.
Interestingly, the distributions for strength, degree, and weight display a
transition from scale-free to exponential form when the parameter with respect
to accelerating growth increases from a small to large value. All the
theoretical predictions are successfully contrasted with extensive numerical
simulations.
| physics.soc-ph |
0704.1693 | N_p N_n Scheme Based on New Empirical Formula for Excitation Energy | We examine the $N_p N_n$ scheme based on a recently proposed simple empirical
formula which is highly valid for the excitation energy of the first excited
natural parity even multipole states in even-even nuclei. We demonstrate
explicitly that the $N_p N_n$ scheme for the excitation energy emerges from the
separate exponential dependence of the excitation energy on the valence nucleon
numbers $N_p$ and $N_n$ together with the fact that only a limited set of
numbers is allowed for the $N_p$ and $N_n$ of the existing nuclei.
| nucl-th |
0704.1694 | Locally Decodable Codes From Nice Subsets of Finite Fields and Prime
Factors of Mersenne Numbers | A k-query Locally Decodable Code (LDC) encodes an n-bit message x as an N-bit
codeword C(x), such that one can probabilistically recover any bit x_i of the
message by querying only k bits of the codeword C(x), even after some constant
fraction of codeword bits has been corrupted. The major goal of LDC related
research is to establish the optimal trade-off between length and query
complexity of such codes.
Recently [Y] introduced a novel technique for constructing locally decodable
codes and vastly improved the upper bounds for code length. The technique is
based on Mersenne primes. In this paper we extend the work of [Y] and argue
that further progress via these methods is tied to progress on an old number
theory question regarding the size of the largest prime factors of Mersenne
numbers.
Specifically, we show that every Mersenne number m=2^t-1 that has a prime
factor p>m^\gamma yields a family of k(\gamma)-query locally decodable codes of
length Exp(n^{1/t}). Conversely, if for some fixed k and all \epsilon > 0 one
can use the technique of [Y] to obtain a family of k-query LDCs of length
Exp(n^\epsilon); then infinitely many Mersenne numbers have prime factors arger
than known currently.
| cs.CC math.NT |
0704.1695 | Pair production with neutrinos in an intense background magnetic field | We present a detailed calculation of the electron-positron production rate
using neutrinos in an intense background magnetic field. The computation is
done for the process nu -> nu e- e+ (where nu can be nu_e, nu_mu, or nu_tau)
within the framework of the Standard Model. Results are given for various
combinations of Landau-levels over a range of possible incoming neutrino
energies and magnetic field strengths.
| hep-ph astro-ph |
0704.1696 | Theoretical Aspects of the SOM Algorithm | The SOM algorithm is very astonishing. On the one hand, it is very simple to
write down and to simulate, its practical properties are clear and easy to
observe. But, on the other hand, its theoretical properties still remain
without proof in the general case, despite the great efforts of several
authors. In this paper, we pass in review the last results and provide some
conjectures for the future work.
| math.ST stat.TH |
0704.1697 | Effect of the Spatial Dispersion on the Shape of a Light Pulse in a
Quantum Well | Reflectance, transmittance and absorbance of a symmetric light pulse, the
carrying frequency of which is close to the frequency of interband transitions
in a quantum well, are calculated. Energy levels of the quantum well are
assumed discrete, and two closely located excited levels are taken into
account. A wide quantum well (the width of which is comparable to the length of
the light wave, corresponding to the pulse carrying frequency) is considered,
and the dependance of the interband matrix element of the momentum operator on
the light wave vector is taken into account. Refractive indices of barriers and
quantum well are assumed equal each other. The problem is solved for an
arbitrary ratio of radiative and nonradiative lifetimes of electronic
excitations. It is shown that the spatial dispersion essentially affects the
shapes of reflected and transmitted pulses. The largest changes occur when the
radiative broadening is close to the difference of frequencies of interband
transitions taken into account.
| cond-mat.mes-hall |
0704.1698 | The origin of the anomalously strong influence of out-of-plane disorder
on high-Tc superconductivity | The electronic structure of Bi2Sr2-xRxCuOy(R=La, Eu) near the (pi,0) point of
the first Brillouin zone was studied by means of angle-resolved photoemission
spectroscopy (ARPES). The temperature T* above which the pseudogap structure in
the ARPES spectrum disappears was found to have an R dependence that is
opposite to that ofthe superconducting transition temperature Tc. This
indicates that the pseudogap state is competing with high-Tc superconductivity,
and the large Tc suppression observed with increasing the out-of-plane disorder
is due to the stabilization of the pseudogap state.
| cond-mat.supr-con cond-mat.str-el |
0704.1699 | Relativistic Hydrodynamics at RHIC and LHC | Recent development of a hydrodynamic model is discussed by putting an
emphasis on realistic treatment of the early and late stages in relativistic
heavy ion collisions. The model, which incorporates a hydrodynamic description
of the quark-gluon plasma with a kinetic approach of hadron cascades, is
applied to analysis of elliptic flow data at the Relativistic Heavy Ion
Collider energy. It is predicted that the elliptic flow parameter based on the
hybrid model increases with the collision energy up to the Large Hadron
Collider energy.
| nucl-th hep-ph nucl-ex |
0704.1700 | Retract rationality and Noether's problem | Let K be any field and G be a finite group. We will prove that, if K is any
field, p an odd prime number, and G is a non-abelian group of exponent p with
|G|=p^3 or p^4 satisfying [K(\zeta_p):K] <= 2, then K(G) is rational over K. We
will also show that K(G) is retract rational if G belongs to a much larger
class of p-groups. In particular, generic G-polynomials of G-Galois extensions
exist for these groups.
| math.AC math.RA |