15 research outputs found
Large-N transition temperature for superconducting films in a magnetic field
We consider the -component Ginzburg-Landau model in the large limit,
the system being embedded in an external constant magnetic field and confined
between two parallel planes a distance apart from one another. On physical
grounds, this corresponds to a material in the form of a film in the presence
of an external magnetic field. Using techniques from dimensional and
-function regularization, modified by the external field and the
confinement conditions, we investigate the behavior of the system as a function
of the film thickness . This behavior suggests the existence of a minimal
critical thickness below which superconductivity is suppressed.Comment: Revtex, two column, 4 pages, 2 figure
Spontaneous Symmetry Breaking in Compactified Theory
We consider the massive vector -component theory
in Euclidian space and, using an extended Matsubara formalism we perform a
compactification on a -dimensional subspace, . This allows us to
treat jointly the effect of temperature and spatial confinement in the
effective potential of the model, setting forth grounds for an analysis of
phase transitions driven by temperature and spatial boundary. For , which
corresponds to the heated system confined between two parallel planes
(separation ), we obtain, in the large limit at one-loop order, formulas
for temperature- and boundary-dependent mass and coupling constant. The
equation for the critical curve in the plane is also derived.Comment: LATEX, 11 pages no figure
Non-Commutative Complete Mellin Representation for Feynman Amplitudes
We extend the complete Mellin (CM) representation of Feynman amplitudes to
the non-commutative quantum field theories. This representation is a versatile
tool. It provides a quick proof of meromorphy of Feynman amplitudes in
parameters such as the dimension of space-time. In particular it paves the road
for the dimensional renormalization of these theories. This complete Mellin
representation also allows the study of asymptotic behavior under rescaling of
arbitrary subsets of external invariants of any Feynman amplitude.Comment: 14 pages, no figur
Halperin-Lubensky-Ma effect in type-I superconducting films
In this note we employ concurrently techniques of generalized
-functions and compactification methods introduced in previous
publications, to study the Halperin-Lubensky-Ma theory of induced weak
first-order phase transitions applied to type-I superconducting films. We
obtain closed formulas to the critical temperature and to the size temperature
as functions of the film thickness.Comment: 4 pages, RevTex
Vacuum polarization in dimensions
We study the main properties of the one-loop vacuum polarization function
() for spinor in ` dimensions', i.e., with
fields defined on such that , with bag-like boundary conditions on
the boundary . We obtain
an exact expression for the induced current due to an external constant
electric field normal to the boundary. We show that, for the particular case of
2+1 dimensions, there is a transverse component for the induced current, which
is localized on a region close to . This current is a
parity breaking effect purely due to the boundary.Comment: 11 pages, no figure
One-loop dimensional reduction of the linear sigma model
We perform the dimensional reduction of the linear model at one-loop
level. The effective potential of the reduced theory obtained from the
integration over the nonzero Matsubara frequencies is exhibited. Thermal mass
and coupling constant renormalization constants are given, as well as the
thermal renormalization group equation which controls the dependence of the
counterterms on the temperature. We also recover, for the reduced theory, the
vacuum unstability of the model for large N.Comment: 19 pages, Latex, no figures, to be submitted to Physica
Finite-size effects on the chiral phase diagram of four-fermion models in four dimensions
We study the size dependence of the dynamical symmetry breaking in the
four-dimensional Nambu-Jona-Lasinio model. We show that the presence of
boundaries reduces the chiral breaking region, and this effect is strengthened
for a larger number of compactified dimensions. A critical value for the length
of the compactified dimensions exists, below which the dynamical symmetry
breaking is not possible. Considering finite temperature and chemical
potential, the chiral phase structure for the system with compactified
dimensions is obtained. A gradual decreasing of the chiral breaking region with
increasing of chemical potential is found. Also, at fixed chemical potential,
the decreasing of the size of the system changes the order of the chiral phase
transition.Comment: LATEX 14 pages 2 figure
The thermal coupling constant and the gap equation in the model
By the concurrent use of two different resummation methods, the composite
operator formalism and the Dyson-Schwinger equation, we re-examinate the
behavior at finite temperature of the O(N)-symmetric model in
a generic D-dimensional Euclidean space. In the cases D=3 and D=4, an analysis
of the thermal behavior of the renormalized squared mass and coupling constant
are done for all temperatures. It results that the thermal renormalized squared
mass is positive and increases monotonically with the temperature. The behavior
of the thermal coupling constant is quite different in odd or even dimensional
space. In D=3, the thermal coupling constant decreases up to a minimum value
diferent from zero and then grows up monotonically as the temperature
increases. In the case D=4, it is found that the thermal renormalized coupling
constant tends in the high temperature limit to a constant asymptotic value.
Also for general D-dimensional Euclidean space, we are able to obtain a formula
for the critical temperature of the second order phase transition. This formula
agrees with previous known values at D=3 and D=4.Comment: 23 pages, 4 figure
Dressed States Approach to Quantum Systems
Using the non-perturbative method of {\it dressed} states previously
introduced in JPhysA, we study effects of the environment on a quantum
mechanical system, in the case the environment is modeled by an ensemble of non
interacting harmonic oscillators. This method allows to separate the whole
system into the {\it dressed} mechanical system and the {\it dressed}
environment, in terms of which an exact, non-perturbative approach is possible.
When applied to the Brownian motion, we give explicit non-perturbative formulas
for the classical path of the particle in the weak and strong coupling regimes.
When applied to study atomic behaviours in cavities, the method accounts very
precisely for experimentally observed inhibition of atomic decay in small
cavities PhysLA, physics0111042