10,389 research outputs found
Entanglement, BEC, and superfluid-like behavior of two-mode photon systems
A system of two interacting photon modes, without constraints on the photon
number, in the presence of a Kerr nonlinearity, exhibits BEC if the transfer
amplitude is greater than the mode frequency. A symmetry-breaking field (SBF)
can be introduced by taking into account a classical electron current. The
ground state, in the limit of small nonlinearity, becomes a squeezed state, and
thus the modes become entangled. The smaller is the SBF, the greater is
entanglement. Superfluid-like behavior is observed in the study of entanglement
growth from an initial coherent state, since in the short-time range the growth
does not depend on the SBF amplitude, and on the initial state amplitude. On
the other hand, the latter is the only parameter which determines entanglement
in the absence of the SBF
A systematic analysis of X-ray afterglows of gamma-ray burst observed by XMM-Newton
This work is part of a systematic re-analysis program of all the data of
Gamma-Ray Burst (GRB) X-ray afterglows observed so far, in order to constrain
the GRB models. We present here a systematic analysis of those afterglows
observed by XMM-Newton between January 2000 and March 2004. This dataset
includes GRB 011211 and GRB 030329. We have obtained spectra, light curves and
colors for these afterglows. In this paper we focus on the continuum spectral
and temporal behavior. We compare these values with the theoretical ones
expected from the fireball model. We derive constraints about the burst
environment (absorption, density profile) and put constraints on their beaming
angle.Comment: 7 pages, 2 figures, COSPAR proceeding accepted for publication in
Advances in Space Researc
Shear instability in skin tissue
We propose two toy-models to describe, predict, and interpret the wrinkles
appearing on the surface of skin when it is sheared. With the first model, we
account for the lines of greatest tension present in human skin by subjecting a
layer of soft tissue to a pre-stretch, and for the epidermis by endowing one of
the layer's faces with a surface tension. For the second model, we consider an
anisotropic model for the skin, to reflect the presence of stiff collagen
fibres in a softer elastic matrix. In both cases, we find an explicit
bifurcation criterion, linking geometrical and material parameters to a
critical shear deformation accompanied by small static wrinkles, with decaying
amplitudes normal to the free surface of skin
An exact solution for the KPZ equation with flat initial conditions
We provide the first exact calculation of the height distribution at
arbitrary time of the continuum KPZ growth equation in one dimension with
flat initial conditions. We use the mapping onto a directed polymer (DP) with
one end fixed, one free, and the Bethe Ansatz for the replicated attractive
boson model. We obtain the generating function of the moments of the DP
partition sum as a Fredholm Pfaffian. Our formula, valid for all times,
exhibits convergence of the free energy (i.e. KPZ height) distribution to the
GOE Tracy Widom distribution at large time.Comment: 4 pages, no figur
Lepton asymmetry and primordial nucleosynthesis in the era of precision cosmology
We calculate and display the primordial light-element abundances as a
function of a neutrino degeneracy parameter \xi common to all flavors. It is
the only unknown parameter characterizing the thermal medium at the primordial
nucleosynthesis epoch. The observed primordial helium abundance Y_p is the most
sensitive cosmic ``leptometer.'' Adopting the conservative Y_p error analysis
of Olive and Skillman implies -0.04 \alt \xi \alt 0.07 whereas the errors
stated by Izotov and Thuan imply \xi=0.0245+-0.0092 (1 sigma). Improved
determinations of the baryon abundance have no significant impact on this
situation. A determination of Y_p that reliably distinguishes between a
vanishing or nonvanishing \xi is a crucial test of the cosmological standard
assumption that sphaleron effects equilibrate the cosmic lepton and baryon
asymmetries.Comment: 5 pages, 2 figures; minor changes, references added, replaced to
match the published version in PRD (Brief Reports
Time-dependence of correlation functions following a quantum quench
We show that the time-dependence of correlation functions in an extended
quantum system in d dimensions, which is prepared in the ground state of some
hamiltonian and then evolves without dissipation according to some other
hamiltonian, may be extracted using methods of boundary critical phenomena in
d+1 dimensions. For d=1 particularly powerful results are available using
conformal field theory. These are checked against those available from solvable
models. They may be explained in terms of a picture, valid more generally,
whereby quasiparticles, entangled over regions of the order of the correlation
length in the initial state, then propagate classically through the system.Comment: 4+ pages, Corrected Typo
The expectation hypothesis of the term structure of very short-term rates: statistical tests and economic value
This paper re-examines the validity of the Expectation Hypothesis (EH) of the term structure of US repo rates ranging in maturity from overnight to three months. We extend the work of Longstaff (2000a) in two directions: (i) we implement statistical tests designed to increase test power in this context; (ii) more importantly, we assess the economic value of departures from the EH based on criteria of profitability and economic significance in the context of a simple trading strategy. The EH is rejected throughout the term structure examined on the basis of the statistical tests. However, the results of our economic analysis are favorable to the EH, suggesting that the statistical rejections of the EH in the repo market are economically insignificant.Interest rates
A Correlation Between the Intrinsic Brightness and Average Decay Rate of Gamma-ray Burst X-ray Afterglow Light Curves
We present a correlation between the average temporal decay
({\alpha}X,avg,>200s) and early-time luminosity (LX,200s) of X-ray afterglows
of gamma-ray bursts as observed by Swift-XRT. Both quantities are measured
relative to a rest frame time of 200 s after the {\gamma}-ray trigger. The
luminosity average decay correlation does not depend on specific temporal
behavior and contains one scale independent quantity minimizing the role of
selection effects. This is a complementary correlation to that discovered by
Oates et al. (2012) in the optical light curves observed by Swift-UVOT. The
correlation indicates that on average, more luminous X-ray afterglows decay
faster than less luminous ones, indicating some relative mechanism for energy
dissipation. The X-ray and optical correlations are entirely consistent once
corrections are applied and contamination is removed. We explore the possible
biases introduced by different light curve morphologies and observational
selection effects, and how either geometrical effects or intrinsic properties
of the central engine and jet could explain the observed correlation.Comment: Accepted for Publication in ApJ; 16 pages, 15 figures, 2 table
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