20,130 research outputs found
Evolution of Intermediate-Mass Black Hole X-Ray Binaries
The majority of the ultraluminous X-ray sources (ULXs) in external galaxies
are believed to be accreting black holes in binary systems; some of the black
holes could be as massive as \sim 100-1000 \ms. We have performed evolution
calculations for intermediate-mass black hole X-ray binaries, assuming they are
formed in dense star clusters via tidal capture. The results are compared with
those for stellar-mass black holes X-ray binaries. We find that these two types
of black holes may have similar companion stars and binary orbits if observed
as ULXs. However, intermediate-mass black holes seem to be favored in
explaining the most luminous ULXs. We also discuss the possibilities of
transient behavior and beamed emission in the evolution of these binary
systems.Comment: 11 pages, 3 figures. Accepted for publication in ApJ
Moments of a single entry of circular orthogonal ensembles and Weingarten calculus
Consider a symmetric unitary random matrix
from a circular orthogonal ensemble. In this paper, we study moments of a
single entry . For a diagonal entry we give the explicit
values of the moments, and for an off-diagonal entry we give leading
and subleading terms in the asymptotic expansion with respect to a large matrix
size . Our technique is to apply the Weingarten calculus for a
Haar-distributed unitary matrix.Comment: 17 page
Deformations of as Yang-Baxter sigma models
We consider a family of deformations of T^{1,1} in the Yang-Baxter sigma
model approach. We first discuss a supercoset description of T^{1,1}, which
makes manifest the full symmetry of the space and leads to the standard
Sasaki-Einstein metric. Next, we consider three-parameter deformations of
T^{1,1} by using classical r-matrices satisfying the classical Yang-Baxter
equation (CYBE). The resulting metric and NS-NS two-form agree exactly with the
ones obtained via TsT transformations, and contain the Lunin-Maldacena
background as a special case. It is worth noting that for AdS_5 x T^{1,1},
classical integrability for the full sector has been argued to be lost. Hence
our result indicates that the Yang-Baxter sigma model approach is applicable
even for non-integrable cosets. This observation suggests that the gravity/CYBE
correspondence can be extended beyond integrable cases.Comment: 21 pages, no figure, LaTeX, v2:clarifications and references added,
v3:minor corrections, further clarifications adde
Straight Round the Twist: Frustration and Chirality in Smectics-A
Frustration is a powerful mechanism in condensed matter systems, driving both
order and co plexity. In smectics, the frustration between macroscopic
chirality and equally spaced layers generates textures characterised by a
proliferation of defects. In this article, we study several different ground
states of the chiral Landau-de Gennes free energy for a smectic liquid crystal.
The standard theory finds the twist grain boundary (TGB) phase to be the ground
state for chiral type II smectics. However, for very highly chiral systems, the
hierarchical helical nanofilament (HN) phase can form and is stable over the
TGB.Comment: 9 pages, 3 figures, submitted to J. Interface Focu
New Kinetic Equation for Pair-annihilating Particles: Generalization of the Boltzmann Equation
A convenient form of kinetic equation is derived for pair annihilation of
heavy stable particles relevant to the dark matter problem in cosmology. The
kinetic equation thus derived extends the on-shell Boltzmann equation in a most
straightforward way, including the off-shell effect. A detailed balance
equation for the equilibrium abundance is further analyzed. Perturbative
analysis of this equation supports a previous result for the equilibrium
abundance using the thermal field theory, and gives the temperature power
dependence of equilibrium value at low temperatures. Estimate of the relic
abundance is possible using this new equilibrium abundance in the sudden
freeze-out approximation.Comment: 19 pages, LATEX file with 2 PS figure
Outflows driven by Giant Protoplanets
We investigate outflows driven by a giant protoplanet using three-dimensional
MHD nested grid simulations. We consider a local region around the protoplanet
in the protoplanetary disk, and calculate three models: (a) unmagnetized disk
model, (b) magnetized disk model having magnetic field azimuthally parallel to
the disk, and (c) magnetic field perpendicular to the disk. Outflows with
velocities, at least, 10 km/s are driven by the protoplanets in both magnetized
disk models, while outflow does not appear in unmagnetized disk model.
Tube-like outflows along the azimuthal direction of the protoplanetary disk
appear in model with magnetic field being parallel to the disk. In this model,
the magnetically dominated regions (i.e., density gap) are clearly contrasted
from other regions and spiral waves appear near the protoplanet. On the other
hand, in model with magnetic field being perpendicular to the disk, outflows
are driven by a protoplanet with cone-like structure just as seen in the
outflow driven by a protostar. Magnetic field lines are strongly twisted near
the protoplanet and the outflows have well-collimated structures in this
model.These outflows can be landmarks for searching exo-protoplanets in their
formation stages. Our results indicate that the accretion rate onto the
protoplanet tend to have a larger value than that expected from previous
hydrodynamical calculations, since a fraction of the angular momentum of
circum-planetary disk is removed by outflows, enhanced non-axisymmetric
patterns caused by magnetic field, and magnetic braking. Possible implications
for observation are also briefly discussed.Comment: 11 pages, 3 figures, Submitted to ApJL, For high resolution figures
see http://www2.scphys.kyoto-u.ac.jp/~machidam/jupiter/doc/resubmit_0703.pd
Entanglement Cost of Antisymmetric States and Additivity of Capacity of Some Quantum Channel
We study the entanglement cost of the states in the contragredient space,
which consists of -dimensional systems. The cost is always ebits when the state is divided into bipartite \C^d \otimes
(\C^d)^{d-2}. Combined with the arguments in \cite{Matsumoto02}, additivity of
channel capacity of some quantum channels is also shown.Comment: revtex 4 pages, no figures, small changes in title and author's
affiliation and some typo are correcte
Temperature Power Law of Equilibrium Heavy Particle Density
A standard calculation of the energy density of heavy stable particles that
may pair-annihilate into light particles making up thermal medium is performed
to second order of coupling, using the technique of thermal field theory. At
very low temperatures a power law of temperature is derived for the energy
density of the heavy particle. This is in sharp contrast to the exponentially
suppressed contribution estimated from the ideal gas distribution function. The
result supports a previous dynamical calculation based on the Hartree
approximation, and implies that the relic abundance of dark matter particles is
enhanced compared to that based on the Boltzmann equation.Comment: 12 pages, LATEX file with 6 PS figure
Boltzmann Suppression of Interacting Heavy Particles
Matsumoto and Yoshimura have recently argued that the number density of heavy
particles in a thermal bath is not necessarily Boltzmann-suppressed for T << M,
as power law corrections may emerge at higher orders in perturbation theory.
This fact might have important implications on the determination of WIMP relic
densities. On the other hand, the definition of number densities in a
interacting theory is not a straightforward procedure. It usually requires
renormalization of composite operators and operator mixing, which obscure the
physical interpretation of the computed thermal average. We propose a new
definition for the thermal average of a composite operator, which does not
require any new renormalization counterterm and is thus free from such
ambiguities. Applying this definition to the model of Matsumoto and Yoshimura
we find that it gives number densities which are Boltzmann-suppressed at any
order in perturbation theory. We discuss also heavy particles which are
unstable already at T=0, showing that power law corrections do in general
emerge in this case.Comment: 7 pages, 5 figures. New section added, with the discussion of the
case of an unstable heavy particle. Version to appear on Phys. Rev.
Time evolution of a thin black ring via Hawking radiation
Black objects lose their mass and angular momenta through evaporation by
Hawking radiation, and the investigation of their time evolution has a long
history. In this paper, we study this problem for a five-dimensional doubly
spinning black ring. The black ring is assumed to emit only massless scalar
particles. We consider a thin black ring with a small thickness parameter,
, which can be approximated by a boosted Kerr string locally. We
show that a thin black ring evaporates with fixing its thickness parameter
. Further, in the case of an Emparan-Reall black ring, we derive
analytic formulas for the time evolution, which has one parameter to be
evaluated numerically. We find that the lifetime of a thin black ring is
shorter by a factor of compared to a five-dimensional
Schwarzschild black hole with the same initial mass. We also study detailed
properties of the Hawking radiation from the thin black ring, including the
energy and angular spectra of emitted particles.Comment: 28 pages, 6 figure
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