308 research outputs found
Klein-Gordon and Dirac particles in non-constant scalar-curvature background
The Klein-Gordon and Dirac equations are considered in a semi-infinite lab
() in the presence of background metrics and with . These metrics have non-constant scalar-curvatures. Various aspects of the
solutions are studied. For the first metric with , it is shown
that the spectrums are discrete, with the ground state energy for spin-0 particles. For , the spectrums are
found to be continuous. For the second metric with , each
particle, depends on its transverse-momentum, can have continuous or discrete
spectrum. For Klein-Gordon particles, this threshold transverse-momentum is
, while for Dirac particles it is . There is no solution for
case. Some geometrical properties of these metrics are also
discussed.Comment: 14 pages, LaTeX, to be published in Int. Jour. Mod. Phys.
Non-Douglas-Kazakov phase transition of two-dimensional generalized Yang-Mills theories
In two-dimensional Yang-Mills and generalized Yang-Mills theories for large
gauge groups, there is a dominant representation determining the thermodynamic
limit of the system. This representation is characterized by a density the
value of which should everywhere be between zero and one. This density itself
is determined through a saddle-point analysis. For some values of the parameter
space, this density exceeds one in some places. So one should modify it to
obtain an acceptable density. This leads to the well-known Douglas-Kazakov
phase transition. In generalized Yang-Mills theories, there are also regions in
the parameter space where somewhere this density becomes negative. Here too,
one should modify the density so that it remains nonnegative. This leads to
another phase transition, different from the Douglas-Kazakov one. Here the
general structure of this phase transition is studied, and it is shown that the
order of this transition is typically three. Using carefully-chosen parameters,
however, it is possible to construct models with phase-transition orders not
equal to three. A class of these non-typical models are also studied.Comment: 11 pages, accepted for publication in Eur. Phys. J.
Cosmological coincidence problem in interacting dark energy models
An interacting dark energy model with interaction term is considered. By studying the model near the
transition time, in which the system crosses the w=-1 phantom-divide-line, the
conditions needed to overcome the coincidence problem is investigated. The
phantom model, as a candidate for dark energy, is considered and for two
specific examples, the quadratic and exponential phantom potentials, it is
shown that it is possible the system crosses the w=-1 line, meanwhile the
coincidence problem is alleviated, the two facts that have root in
observations.Comment: 15 pages, LaTeX. Some minor explanations are added. To be published
in Phys. Rev.
A new class of integrable diffusion-reaction processes
We consider a process in which there are two types of particles, A and B, on
an infinite one-dimensional lattice. The particles hop to their adjacent sites,
like the totally asymmetric exclusion process (ASEP), and have also the
following interactions: A+B -> B+B and B+A -> B+B, all occur with equal rate.
We study this process by imposing four boundary conditions on ASEP master
equation. It is shown that this model is integrable, in the sense that its
N-particle S-matrix is factorized into a product of two-particle S-matrices
and, more importantly, the two-particle S-matrix satisfy quantum Yang-Baxter
equation. Using coordinate Bethe-ansatz, the N-particle wavefunctions and the
two-particle conditional probabilities are found exactly.
Further, by imposing four reasonable physical conditions on two-species
diffusion-reaction processes (where the most important ones are the equality of
the reaction rates and the conservation of the number of particles in each
reaction), we show that among the 4096 types of the interactions which have
these properties and can be modeled by a master equation and an appropriate set
of boundary conditions, there are only 28 independent interactions which are
integrable. We find all these interactions and also their corresponding wave
functions. Some of these may be new solutions of quantum Yang-Baxter equation.Comment: LaTex,16 pages, some typos are corrected, will be appeared in Phys.
Rev. E (2000
Spin 0 and spin 1/2 particles in a spherically symmetric static gravity and a Coulomb field
A relativistic particle in an attractive Coulomb field as well as a static
and spherically symmetric gravitational field is studied. The gravitational
field is treated perturbatively and the energy levels are obtained for both
spin 0 (Klein-Gordon) and spin 1/2 (Dirac) particles. The results are shown to
coincide with each other as well as the result of the nonrelativistic
(Schrodinger) equation in the nonrelativistic limit.Comment: 12 page
Transition from quintessence to phantom phase in quintom model
Assuming the Hubble parameter is a continuous and differentiable function of
comoving time, we investigate necessary conditions for quintessence to phantom
phase transition in quintom model. For power-law and exponential potential
examples, we study the behavior of dynamical dark energy fields and Hubble
parameter near the transition time, and show that the phantom-divide-line w=-1
is crossed in these models.Comment: LaTeX, 19 pages, four figures, some minor changes in Introduction,
two figures added and the references updated, accepted for publication in
Phys. Rev.
Neutrino oscillation in a space-time with torsion
Using the Einstein-Cartan-Dirac theory, we study the effect of torsion on
neutrino oscillation. We see that torsion cannot induce neutrino oscillation,
but affects it whenever oscillation exists for other reasons. We show that the
torsion effect on neutrino oscillation is as important as the neutrino mass
effect, whenever the ratio of neutrino number density to neutrino energy is
cm /eV, or the number density of the matter is cm.Comment: 7 pages, LaTex,Some typos corrected Journal: Int. J. Mod. Phys. A
(1999) (will be appeared
Remarks on generalized Gauss-Bonnet dark energy
The modified gravity with F(R,G) Lagrangian, G is the Gauss-Bonnet invariant,
is considered. It is shown that the phantom-divide-line crossing and the
deceleration to acceleration transition generally occur in these models. Our
results coincide with the known results of f(R)-gravity and f(G)-gravity
models. The contribution of quantum effects to these transitions is calculated,
and it is shown that in some special cases where there are no transitions in
classical level, quantum contributions can induce transitions. The quantum
effects are described via the account of conformal anomaly.Comment: 11 pages, LaTeX, a paragraph added, to be appeared in Phys. Rev.
Torsion Phenomenology at the LHC
We explore the potential of the CERN Large Hadron Collider (LHC) to test the
dynamical torsion parameters. The form of the torsion action can be established
from the requirements of consistency of effective quantum field theory. The
most phenomenologically relevant part of the torsion tensor is dual to a
massive axial vector field. This axial vector has geometric nature, that means
it does not belong to any representation of the gauge group of the SM extension
or GUT theory. At the same time, torsion should interact with all fermions,
that opens the way for the phenomenological applications.
We demonstrate that LHC collider can establish unique constraints on the
interactions between fermions and torsion field considerably exceeding present
experimental lower bounds on the torsion couplings and its mass. It is also
shown how possible non-universal nature of torsion couplings due to the
renormalization group running between the Planck and TeV energy scales can be
tested via the combined analysis of Drell-Yan and production
processes
Electrostatic self-energy and Bekenstein entropy bound in the massive Schwinger model
We obtain the electrostatic energy of two opposite charges near the horizon
of stationary black-holes in the massive Schwinger model. Besides the confining
aspects of the model, we discuss the Bekenstein entropy upper bound of a
charged object using the generalized second law. We show that despite the
massless case, in the massive Schwinger model the entropy of the black hole and
consequently the Bekenstein bound are altered by the vacuum polarization.Comment: 14 pages, accepted for publication in "Gen. Rel. Grav. (2005)
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