43,488 research outputs found
A New Model for the Hard Time Lags in Black Hole X-Ray Binaries
The time-dependent Comptonized output of a cool soft X-ray source drifting
inward through an inhomogeneous hot inner disk or corona is numerically
simulated. We propose that this scenario can explain from first principles the
observed trends in the hard time lags and power spectra of the rapid aperiodic
variability of the X-ray emission of Galactic black-hole candidates.Comment: 10 pages, including 2 figures; uses epsf.sty, rotate.sty; accepted
for ApJ Letter
Quantum Phase Interference for Quantum Tunneling in Spin Systems
The point-particle-like Hamiltonian of a biaxial spin particle with external
magnetic field along the hard axis is obtained in terms of the potential field
description of spin systems with exact spin-coordinate correspondence. The
Zeeman energy term turns out to be an effective gauge potential which leads to
a nonintegrable pha se of the Euclidean Feynman propagator.
The phase interference between clockwise and anticlockwise under barrier
propagations is recognized explicitly as the Aharonov-Bohm effect. An
additional phase which is significant for quantum phase interference is
discovered with the quantum theory of spin systems besides the known phase
obtained with the semiclassical treatment of spin. We also show the energ y
dependence of the effect and obtain the tunneling splitting at excited states
with the help of periodic instantons.Comment: 19 pages, no figure, to appear in PR
Phase structure of lattice QCD with two flavors of Wilson quarks at finite temperature and chemical potential
We present results for phase structure of lattice QCD with two degenerate
flavors () of Wilson quarks at finite temperature and small baryon
chemical potential . Using the imaginary chemical potential for which
the fermion determinant is positive, we perform simulations at points where the
ratios of pseudo-scalar meson mass to the vector meson mass are
between and as well as in the quenched limit. By analytic
continuation to real quark chemical potential , we obtain the transition
temperature as a function of small . We attempt to determine the nature
of transition at imaginary chemical potential by histogram, MC history, and
finite size scaling. In the infinite heavy quark limit, the transition is of
first order. At intermediate values of quark mass corresponding to the
ratio of in the range from to at
, the MC simulations show absence of phase transition.Comment: 10 pages, 17 figures;16 figures;9 pages,10 figures;10 pages,11
figure
Spin transfer and polarization of antihyperons in lepton induced reactions
We study the polarization of antihyperon in lepton induced reactions such as
and with polarized beams using
different models for spin transfer in high energy fragmentation processes. We
compare the results with the available data and those for hyperons. We make
predictions for future experiments.Comment: 31 pages, 6 figures. submitted to Phys. Rev. D. content changed,
references adde
Constraining and Dark Energy with Gamma-Ray Bursts
An relationship with a small
scatter for current -ray burst (GRB) data was recently reported, where
is the beaming-corrected -ray energy and
is the peak energy in the local observer frame. By considering this
relationship for a sample of 12 GRBs with known redshift, peak energy, and
break time of afterglow light curves, we constrain the mass density of the
universe and the nature of dark energy. We find that the mass density
(at the confident level) for a flat
universe with a cosmological constant, and the parameter of an assumed
static dark-energy equation of state ().
Our results are consistent with those from type Ia supernovae. A larger sample
established by the upcoming {\em Swift} satellite is expected to provide
further constraints.Comment: 8 pages including 4 figures, to appear in ApJ Letters, typos
correcte
Scaling of geometric phases close to quantum phase transition in the XY chain
We show that geometric phase of the ground state in the XY model obeys
scaling behavior in the vicinity of a quantum phase transition. In particular
we find that geometric phase is non-analytical and its derivative with respect
to the field strength diverges at the critical magnetic field. Furthermore,
universality in the critical properties of the geometric phase in a family of
models is verified. In addition, since quantum phase transition occurs at a
level crossing or avoided level crossing and these level structures can be
captured by Berry curvature, the established relation between geometric phase
and quantum phase transitions is not a specific property of the XY model, but a
very general result of many-body systems.Comment: 4 page
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