Georgios Metikas

Non-analytic vertex renormalization of a Bose gas at finite temperature

We derive the flow equations for the symmetric phase of a dilute three-dimensional Bose gas. We point out that the flow equation for the interaction contains parts which are non-analytic at the origin of the frequency–momentum space. We examine the way this non-analyticity affects the fixed point of the system of the flow equations and shifts the value of the critical exponent for the correlation length in comparison with previous work where the non-analyticity was neglected. Finally, we emphasize the purely thermal nature of this non-analytic behaviour comparing our approach to a previous work where non-analyticity was studied in the context of renormalization at zero temperature.

Effective action for QED in 2+1 dimensions at finite temperature

We calculate the eective action for a constant magnetic eld and a time-dependent time-component of the gauge eld in 2+1 dimensions at nite temperature. We also discuss the behaviour of the charge density and the fermion condensate as order parameters of symmetry breaking.

Phase transition of trapped interacting Bose gases and the renormalization group

We apply perturbative renormalization-group theory to the symmetric phase of a dilute interacting Bose gas which is trapped in a three-dimensional harmonic potential. Using Wilsons energy-shell renormalization and the {epsilon} expansion, we derive the flow equations for the system. We relate these equations to the flow for the homogeneous Bose gas. In the thermodynamic limit, we apply our approach to examine the transition temperature of the harmonically trapped Bose gas as a function of the scattering length. The results are compared to previous studies of the problem.

The ε expansion in the symmetry-broken phase of an interacting Bose gas at finite temperature

We discuss the application of the momentum-shell renormalization group method to the interacting homogeneous Bose gas in the symmetric and symmetry-broken phases. It is demonstrated that recently discussed discrepancies are artefacts due to not taking proper care of infrared divergencies appearing at finite temperature. If these divergencies are taken into account and treated properly by means of the e expansion, the resulting renormalization group equations and the corresponding universal properties are identical in the symmetric and symmetry-broken phases.

Renormalization group analysis of a confined, interacting Bose gas

Abstract.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 thermodynamic 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, thus changing the thermodynamic properties of the gas.

INFRARED DIVERGENCE IN QED3 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

INFRARED DIVERGENCE INQED3AT FINITE TEMPERATURE

QED_{3}

Infrared divergence in QED

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

_3

1 \over N

at finite temperature

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