392 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.
Berry phase for spin--1/2 particles moving in a spacetime with torsion
Berry phase for a spin--1/2 particle moving in a flat spacetime with torsion
is investigated in the context of the Einstein-Cartan-Dirac model. It is shown
that if the torsion is due to a dense polarized background, then there is a
Berry phase only if the fermion is massless and its momentum is perpendicular
to the direction of the background polarization. The order of magnitude of this
Berry phase is discussed in other theoretical frameworks.Comment: 9 pages. Some typos corrected, a discussion on propagating torsion is
added, accepted for publication in Eur. Phys. J. C (2001
Phase structure of the generalized two dimensional Yang-Mills theories on sphere
We find a general expression for the free energy of
generalized 2D Yang-Mills theories in the strong () region at large .
We also show that in this region, the density function of Young tableau of
these models is a three-cut problem. In the specific model, we show
that the theory has a third order phase transition, like (YM_2) and
models. We have some comments for cases. At the end, we
study the phase structure of model for region.Comment: 13 pages, LaTex,the introduction section was changed,will be appeared
in: Eur. Phys. J. C (1999
A pseudo-conformal representation of the Virasoro algebra
Generalizing the concept of primary fields, we find a new representation of
the Virasoro algebra, which we call it a pseudo-conformal representation. In
special cases, this representation reduces to ordinary- or
logarithmic-conformal field theory. There are, however, other cases in which
the Green functions differ from those of ordinary- or logarithmic-conformal
field theories. This representation is parametrized by two matrices. We
classify these two matrices, and calculate some of the correlators for a simple
example.Comment: LaTex, 5 page
Large-N limit of the generalized 2-dimensional Yang-Mills theories
Using the standard saddle-point method, we find an explicit relation for the
large-N limit of the free energy of an arbitrary generalized 2D Yang-Mills
theory in the weak () region, we
investigate carefully the specific fourth Casimir theory, and show that the
ordinary integral equation of the density function is not adequate to find the
solution. There exist, however, another equation which restricts the
parameters. So one can find the free energy in strong region and show that the
theory has a third order phase transition.Comment: 10 pages, minor typos corrected, one reference update
Quantum reflection of massless neutrinos from a torsion-induced potential
In the context of the Einstein-Cartan-Dirac model, where the torsion of the
space-time couples to the axial currents of the fermions, we study the effects
of this quantum-gravitational interaction on a massless neutrino beam crossing
through a medium with high number density of fermions at rest. We calculate the
reflection amplitude and show that a specific fraction of the incident
neutrinos reflects from this potential if the polarization of the medium is
different from zero. We also discuss the order of magnitude of the fermionic
number density in which this phenomenon is observable, in other theoretical
contexts, for example the strong-gravity regime and the effective field theory
approach.Comment: 8 pages, LaTe
Derivation of quantum theories:symmetries and the exact solution of the derived system
Based on the technique of derivation of a theory, presented in our recent
paper, we investigate the properties of the derived quantum system. We show
that the derived quantum system possesses the (nonanomalous) symmetries of the
original one, and prove that the exact Green functions of the derived theory
are expressed in terms of the semiclassically approximated Green functions of
the original theory.Comment: 8 pages,LaTe
Models solvable through the empty-interval method
The most general one dimensional reaction-diffusion model with
nearest-neighbor interactions solvable through the empty interval method, and
without any restriction on the particle-generation from two adjacent empty
sites is studied. It is shown that turning on the reactions which generate
particles from two adjacent empty sites, results in a gap in the spectrum of
the evolution operator (or equivalently a finite relaxation time).Comment: 8 page
The phase-space of generalized Gauss-Bonnet dark energy
The generalized Gauss-Bonnet theory, introduced by Lagrangian F(R,G), has
been considered as a general modified gravity for explanation of the dark
energy. G is the Gauss-Bonnet invariant. For this model, we seek the situations
under which the late-time behavior of the theory is the de-Sitter space-time.
This is done by studying the two dimensional phase space of this theory, i.e.
the R-H plane. By obtaining the conditions under which the de-Sitter space-time
is the stable attractor of this theory, several aspects of this problem have
been investigated. It has been shown that there exist at least two classes of
stable attractors : the singularities of the F(R,G), and the cases in which the
model has a critical curve, instead of critical points. This curve is R=12H^2
in R-H plane. Several examples, including their numerical calculations, have
been discussed.Comment: 19 pages, 11 figures, typos corrected, a reference adde
Observables of the generalized 2D Yang-Mills theories on arbitrary surfaces: a path integral approach
Using the path integral method, we calculate the partition function and the
generating functional (of the field strengths) of the generalized 2D Yang-Mills
theories in the Schwinger--Fock gauge. Our calculation is done for arbitrary 2D
orientable, and also nonorientable surfaces.Comment: 6 pages, LaTe
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