15 research outputs found
Renormalization Group Analysis of a Confined, Interacting Bose Gas
The renormalization group is not only a powerful method for describing
universal properties of phase transitions but it is also useful for evaluating
non- universal properties beyond mean-field theory. In this contribution we
concentrate on these latter aspects of the renormalization group approach. We
introduce its main underlying ideas in the familiar context of the ideal Bose
gas and then apply them to the case of an interacting, confined Bose gas within
the framework of the random phase approximation. We model confinement by
periodic boundary conditions and demonstrate how confinement modifies the flow
equations of the renormalization group changing thus the thermodynamic
properties of the gas.Comment: 24 pages, 5 figure
Finite Temperature Time-Dependent Effective Theory For The Goldstone Field In A BCS-Type Superfluid
We extend to finite temperature the time-dependent effective theory for the
Goldstone field (the phase of the pair field) which is appropriate
for a superfluid containing one species of fermions with s-wave interactions,
described by the BCS Lagrangian. We show that, when Landau damping is
neglected, the effective theory can be written as a local time-dependent
non-linear Schr\"{o}dinger Lagrangian (TDNLSL) which preserves the Galilean
invariance of the zero temperature effective theory and is identified with the
superfluid component. We then calculate the relevant Landau terms which are
non-local and which destroy the Galilean invariance. We show that the retarded
-propagator (in momentum space) can be well represented by two poles in
the lower-half frequency plane, describing damping with a predicted
temperature, frequency and momentum dependence. It is argued that the real
parts of the Landau terms can be approximately interpreted as contributing to
the normal fluid component.Comment: 25 pages, 5 figures, references added, Introduction rewritte
Infrared divergence in QED at finite temperature
We consider various ways of treating the infrared divergence which appears in
the dynamically generated fermion mass, when the transverse part of the photon
propagator in N flavour at finite temperature is included in the
Matsubara formalism. This divergence is likely to be an artefact of taking into
account only the leading order term in the expansion when we
calculate the photon propagator and is handled here phenomenologically by means
of an infrared cutoff. Inserting both the longitudinal and the transverse part
of the photon propagator in the Schwinger-Dyson equation we find the dependence
of the dynamically generated fermion mass on the temperature and the cutoff
parameters. It turns out that consistency with certain statistical physics
arguments imposes conditions on the cutoff parameters. For parameters in the
allowed range of values we find that the ratio is approximately 6, consistently with previous calculations which
neglected the transverse photon contribution.Comment: 37 pages, 12 figures, typos corrected, references added, Introduction
rewritte
Effective action for QED in 2+1 dimensions at finite temperature
We calculate the effective action for a constant magnetic field and a
time-dependent time-component of the gauge field in 2+1 dimensions at finite
temperature. We also discuss the behaviour of the charge density and the
fermion condensate as order parameters of symmetry breaking.Comment: Latex, 10 pages, no figure