24,797 research outputs found
Density matrix of chaotic quantum systems
The nonequilibrium dynamics in chaotic quantum systems denies a fully
understanding up to now, even if thermalization in the long-time asymptotic
state has been explained by the eigenstate thermalization hypothesis which
assumes a universal form of the observable matrix elements in the eigenbasis of
Hamiltonian. It was recently proposed that the density matrix elements have
also a universal form, which can be used to understand the nonequilibrium
dynamics at the whole time scale, from the transient regime to the long-time
steady limit. In this paper, we numerically test these assumptions for density
matrix in the models of spins.Comment: 6 pages, 5 figure
Synchrotron Radiation from Electrons with a Pitch-angle Distribution
In most astrophysical processes involving synchrotron radiation, the pitch-angle distribution of the electrons is assumed to be isotropic. However, if electrons are accelerated anisotropically, e.g., in a relativistic shock wave with an ordered magnetic field or in magnetic reconnection regions, the electron pitch angles might be anisotropic. In this Letter, we study synchrotron radiation from electrons with a pitch-angle distribution with respect to a large-scale uniform magnetic field. Assuming that the pitch-angle distribution is normal with a scatter of σ p and that the viewing direction is where the pitch-angle direction peaks, we find that for electrons with a Lorentz factor γ, the observed flux satisfies F ν ∝ ν 2/3 for ν ν cr (ν cr is the critical frequency of synchrotron), if σ p 1/γ is satisfied. On the other hand, if σ p 1/γ, the spectrum below ν cr is a broken power law with a break frequency , e.g., for ν ν br and for . Thus, the ultimate synchrotron line of death is F ν ∝ ν 2/3. We discuss the application of this theory to blazars and gamma-ray bursts
A Refined Holographic QCD Model and QCD Phase Structure
We consider the Einstein-Maxwell-dilaton system with an arbitrary kinetic
gauge function and a dilaton potential. A family of analytic solutions is
obtained by the potential reconstruction method. We then study its holographic
dual QCD model. The kinetic gauge function can be fixed by requesting the
linear Regge spectrum of mesons. We calculate the free energy to obtain the
phase diagram of the holographic QCD model.Comment: 21 pages, 17 figures. arXiv admin note: substantial text overlap with
arXiv:1301.038
Confinement-Deconfinment Phase Transition for Heavy Quarks
We study confinement-deconfinement phase transition for heavy quarks in a
bottom-up holographic QCD model. We consider a black hole background in an
Einstein-Maxwell-scalar system and add probe open strings to the background.
Combining the various configurations of the open strings and the phase
structure of the black hole background itself, we obtain the
confinement-deconfinement phase diagram for heavy quarks in the holographic QCD
model.Comment: 23 pages, 14 figures, published in JHEP. arXiv admin note: text
overlap with arXiv:1301.038
Dispersion Measure Variation of Repeating Fast Radio Burst Sources
The repeating fast radio burst (FRB) 121102 was recently localized in a dwarf
galaxy at a cosmological distance. The dispersion measure (DM) derived for each
burst from FRB 121102 so far has not shown significant evolution, even though
an apparent increase was recently seen with newly detected VLA bursts. It is
expected that more repeating FRB sources may be detected in the future. In this
work, we investigate a list of possible astrophysical processes that might
cause DM variation of a particular FRB source. The processes include (1) the
cosmological scale effects such as Hubble expansion and large-scale structure
fluctuations; (2) the FRB local effects such as gas density fluctuation,
expansion of a supernova remnant, a pulsar wind nebula, and an HII region; and
(3) the propagation effect due to plasma lensing. We find that the DM
variations contributed by the large-scale structure are extremely small, and
any observable DM variation is likely caused by the plasma local to the FRB
source. Besides mechanisms that produce decreasing DM with time, we suggest
that an FRB source in an expanding supernova remnant around a nearly neutral
ambient medium during the deceleration (Sedov-Taylor and snowplow) phases or in
a growing HII region can introduce DM increasing. Some effects (e.g. an FRB
source moving in an HII region or plasma lensing) can give either positive or
negative DM variations. Future observations of DM variations of FRB 121102 and
other repeating FRB sources can bring important clues for the physical origin
of these sources.Comment: 12 pages. Accepted for publication in Ap
Convergence of martingale solution to slow-fast systems with jumps modulated by Markovian switching
This paper investigates the convergence of martingale solutions to slow-fast
systems with jumps modulated by Markovian switching on weakly irreducible
class. The key point here is to deals with slow-fast systems and two-time-scale
Markovian switching simultaneously, while averaging on the slow component
requires two invariant measures respectively due to the coexistence of the fast
component and Markovian switching. We first investigate the slow-fast systems
modulated by Markovian chains with single weakly irreducible class, and the
existence and uniqueness of the solution will be proved. Then weak convergence
is presented based on tightness and the exponential ergodicity of the fast
component with the martingale method, where the appropriate perturbed test
functions plays a decisive role in processing. Finally we extend results to the
case of the multiple irreducible class
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