Variational solution of the Gross-Neveu model at finite temperature in the large N limit

We use a nonperturbative variational method to investigate the phase transition of the Gross-Neveu model. It is shown that the variational procedure can be generalized to the finite temperature case. The large N result for the phase transition is correctly reproduced.Comment: 12 p., 1 fig, this is the version which will appear in the Phys Lett B, it differs from the previous one in what concerns the introduction and conclusions (re written), several references have been adde

Symmetry Aspects in Nonrelativistic Multi-Scalar Field Models and Application to a Coupled Two-Species Dilute Bose Gas

We discuss unusual aspects of symmetry that can happen due to entropic effects in the context of multi-scalar field theories at finite temperature. We present their consequences, in special, for the case of nonrelativistic models of hard core spheres. We show that for nonrelativistic models phenomena like inverse symmetry breaking and symmetry non-restoration cannot take place, but a reentrant phase at high temperatures is shown to be possible for some region of parameters. We then develop a model of interest in studies of Bose-Einstein condensation in dilute atomic gases and discuss about its phase transition patterns. In this application to a Bose-Einstein condensation model, however, no reentrant phases are found.Comment: 8 pages, 1 eps figure, IOP style. Based on a talk given by R. O. Ramos at the QFEXT05 workshop, Barcelona, Spain, September 5-9, 2005. One reference was update

Transition Temperature for Weakly Interacting Homogeneous Bose Gases

We apply the nonperturbative optimized linear δ expansion method to the O(N) scalar field model in three dimensions to determine the transition temperature of a dilute homogeneous Bose gas. Our results show that the shift of the transition temperature ΔTc/Tc of the interacting model, compared with the ideal-gas transition temperature, really behaves as γan1/3 where a is the s-wave scattering length and n is the number density. For N=2 our calculations yield the value γ=3.059