Activity on Thermal Field Theory

I give now a short descriptions of my papers on (near) Equilibrium QFT, made in collaborations involving H.J. De Vega (LPTHE, Paris), D. Boyanovsky (University of Pittsburgh), R. Holman (Carnegie Mellon University).

• [DRG]Dynamical Renormalization Group Resummation of Finite Temperature Infrared Divergences, D. Boyanovsky, H. J. De Vega, R. Holman, M. Simionato, LPTHE-98-08, PITT-98-08, hep-ph/9809346, 36pp. Published in Phys. Rev. D60, 065003, 1999. In this paper we studied the anomalous relaxation of scalar fluctuations in high temperature scalar QED,as a model for understanding the infrared singularities involved in the computation of the fermion damping rate. Consistently with previous work in the literature, [5] we show that the relaxation is non-exponential. The new point is that the infrared divergences are managed by using the Dynamical Renormalization Group approach (DRG). The DRG is a general method of solution for differential equations (initial value problems) which consists in a resummation of the secular terms appearing in the naive perturbative solution, and it is valid even for asymptotically large times. The same method has been successfully applied in a variety of situations [6].
• [CSD] Relaxing near the critical point, D. Boyanovsky, H. J. De Vega, M. Simionato, LPTHE-00-16, hep-ph/0004159 , 41pp. Published in Phys. Rev. D63:045007, 2001. Here we studied the thermalization rate for critical systems. By considering a scalar $O(N)$ model at the critical temperature and working non-perturbatively at next-to-leading order in the large $N$ expansion, we found a critical slowing down behavior for long wavelengths. This means that the time needed to thermalize long wavelengths fluctuations (i.e. homogenous field configurations) increases up to infinity. This fact has phenomenological consequences, since it means that near a second order phase transition one should expect sensible deviation from equilibrium for the distribution functions of soft particles.
• [LP]The Landau Pole at Finite Temperature, H. J. de Vega and M. Simionato, hep-ph/0011268, 6 pp. Published in Phys. Rev. D64: 021703, 2001. This paper differs from the others since it addresses a purely equilibrium issue, i.e. how the position of the ultraviolet Landau pole changes for a trivial theory when the existence of a medium at temperature $T\neq0$ is taken in account. We found analytically in the case of the $O(N)$ linear sigma model that the Landau pole position increases with the temperature, i.e. the range of validity of the theory increases when there are in-medium effects. As a consequence the theory behaves perfectly well even at temperatures well beyond the zero-temperature Landau pole (which I remind can be at low energies for strongly coupled theories, like for instance the pion $O(4)$ model).