342 research outputs found
A Note on the Cosmological Dynamics in Finite-Range Gravity
In this note we consider the homogeneous and isotropic cosmology in the
finite-range gravity theory recently proposed by Babak and Grishchuk. In this
scenario the universe undergoes late time accelerated expansion if both the
massive gravitons present in the model are tachyons. We carry out the phase
space analysis of the system and show that the late-time acceleration is an
attractor of the model.Comment: RevTex, 4 pages, two figures, New references added, To appear in
IJMP
Asymptotic Infrared Fractal Structure of the Propagator for a Charged Fermion
It is well known that the long-range nature of the Coulomb interaction makes
the definition of asymptotic ``in'' and ``out'' states of charged particles
problematic in quantum field theory. In particular, the notion of a simple
particle pole in the vacuum charged particle propagator is untenable and should
be replaced by a more complicated branch cut structure describing an electron
interacting with a possibly infinite number of soft photons. Previous work
suggests a Dirac propagator raised to a fractional power dependent upon the
fine structure constant, however the exponent has not been calculated in a
unique gauge invariant manner. It has even been suggested that the fractal
``anomalous dimension'' can be removed by a gauge transformation. Here, a gauge
invariant non-perturbative calculation will be discussed yielding an
unambiguous fractional exponent. The closely analogous case of soft graviton
exponents is also briefly explored.Comment: Updated with a corrected sign error, longer discussion of fractal
dimension, and more reference
Weakly Interacting, Dilute Bose Gases in 2D
This article surveys a number of theoretical problems and open questions in
the field of two-dimensional dilute Bose gases with weak repulsive
interactions. In contrast to three dimensions, in two dimensions the formation
of long-range order is prohibited by the Bogoliubov-Hohenberg theorem, and
Bose-Einstein condensation is not expected to be realized. Nevertheless, first
experimental indications supporting the formation of the condensate in low
dimensional systems have been recently obtained. This unexpected behaviour
appears to be due to the non-uniformity, introduced into a system by the
external trapping potential. Theoretical predictions, made for homogeneous
systems, require therefore careful reexamination.
We survey a number of popular theoretical treatments of the dilute weakly
interacting Bose gas and discuss their regions of applicability. The
possibility of Bose-Einstein condensation in a two-dimensional gas, the
validity of perturbative t-matrix approximation and diluteness condition are
issues that we discuss in detail.Comment: Survey, 25 pages RMP style, revised version, refs added, some changes
made, accepted for publication in Rev. Mod. Phy
Reduction and Realization in Toda and Volterra
We construct a new symplectic, bi-hamiltonian realization of the KM-system by
reducing the corresponding one for the Toda lattice. The bi-hamiltonian pair is
constructed using a reduction theorem of Fernandes and Vanhaecke. In this paper
we also review the important work of Moser on the Toda and KM-systems.Comment: 17 page
Multitemporal generalization of the Tangherlini solution
The n-time generalization of the Tangherlini solution [1] is considered. The
equations of geodesics for the metric are integrated. For it is shown
that the naked singularity is absent only for two sets of parameters,
corresponding to the trivial extensions of the Tangherlini solution. The motion
of a relativistic particle in the multitemporal background is considered. This
motion is governed by the gravitational mass tensor. Some generalizations of
the solution, including the multitemporal analogue of the Myers-Perry charged
black hole solution, are obtained.Comment: 14 pages. RGA-CSVR-005/9
Spinons, Solitons and Magnons in One-dimensional Heisenberg-Ising Antiferromagnets
We calculate the excitation spectra for the one- Heisenberg-Ising
antiferromagnets by expansions around the Ising limit. For , the
calculated expansion coefficients for the spinon-spectra agree term by term
with the solution of Johnson and McCoy. For , the solitons become gapless
before the Heisenberg limit is reached, signalling a transition to the Haldane
phase. By applying a staggered field we calculate the one-magnon spectra for
the Heisenberg chain. For the quantum renormalization of the
spin-wave spectra is calculated to be approximately .Comment: 4 pages, RevTex, 3 postscript figures, Latex file and figures have
been uuencode
Third quantization: a general method to solve master equations for quadratic open Fermi systems
The Lindblad master equation for an arbitrary quadratic system of n fermions
is solved explicitly in terms of diagonalization of a 4n x 4n matrix, provided
that all Lindblad bath operators are linear in the fermionic variables. The
method is applied to the explicit construction of non-equilibrium steady states
and the calculation of asymptotic relaxation rates in the far from equilibrium
problem of heat and spin transport in a nearest neighbor Heisenberg XY spin 1/2
chain in a transverse magnetic field.Comment: 24 pages, with 8 eps figures - few minor corrections to the published
version, e.g. anti-symmetrizing the matrix given by eq. (27
Non-Abelian Bosonization and Haldane's Conjecture
We study the long wavelength limit of a spin S Heisenberg antiferromagnetic
chain. The fermionic Lagrangian obtained corresponds to a perturbed level 2S
SU(2) Wess-Zumino-Witten model. This effective theory is then mapped into a
compact U(1) boson interacting with Z_{2S} parafermions. The analysis of this
effective theory allows us to show that when S is an integer there is a mass
gap to all excitations, whereas this gap vanishes in the half-odd-integer spin
case. This gives a field theory treatment of the so-called Haldane's conjecture
for arbitrary values of the spin S.Comment: 9 pages REVTeX, no figure
Correlation effects during liquid infiltration into hydrophobic nanoporous mediums
Correlation effects arising during liquid infiltration into hydrophobic
porous medium are considered. On the basis of these effects a mechanism of
energy absorption at filling porous medium by nonwetting liquid is suggested.
In accordance with this mechanism, the absorption of mechanical energy is a
result expenditure of energy for the formation of menisci in the pores on the
shell of the infinite cluster and expenditure of energy for the formation of
liquid-porous medium interface in the pores belonging to the infinite cluster
of filled pores. It was found that in dependences on the porosity and,
consequently, in dependences on the number of filled pores neighbors, the
thermal effect of filling can be either positive or negative and the cycle of
infiltration-defiltration can be closed with full outflow of liquid. It can
occur under certain relation between percolation properties of porous medium
and the energy characteristics of the liquid-porous medium interface and the
liquid-gas interface. It is shown that a consecutive account of these
correlation effects and percolation properties of the pores space during
infiltration allow to describe all experimental data under discussion
Effective spacetime from multi-dimensional gravity
We study the effective spacetimes in lower dimensions that can be extracted
from a multidimensional generalization of the Schwarzschild-Tangherlini
spacetimes derived by Fadeev, Ivashchuk and Melnikov ({\it Phys. Lett,} {\bf A
161} (1991) 98). The higher-dimensional spacetime has
dimensions, where and are the number of "internal" and "external" extra
dimensions, respectively. We analyze the effective spacetime obtained
after dimensional reduction of the external dimensions. We find that when
the extra dimensions are compact (i) the physics in lower dimensions is
independent of and the character of the singularities in higher dimensions,
and (ii) the total gravitational mass of the effective matter distribution
is less than the Schwarzshild mass. In contrast, when the extra dimensions
are large this is not so; the physics in does explicitly depend on
, as well as on the nature of the singularities in high dimensions, and the
mass of the effective matter distribution (with the exception of wormhole-like
distributions) is bigger than the Schwarzshild mass. These results may be
relevant to observations for an experimental/observational test of the theory.Comment: A typo in Eq. (24) is fixe
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