The Quasiparticle Structure of Hot Gauge Theories

The study of the ultrarelativistic plasmas in perturbation theory is plagued with infrared divergences which are not eliminated by the screening corrections. They affect, in particular, the computation of the lifetime of the elementary excitations, thus casting doubt on the validity of the quasiparticle picture. We show that, for Abelian plasmas at least, the infrared problem of the damping rate can be solved by a non-perturbative treatment based on the Bloch-Nordsieck approximation. The resulting expression of the fermion propagator is free of divergences, and exhibits a non-exponential damping at large times: SR(t) ∼ exp{−αT t lnωpt}, where ωp = gT/3 is the plasma frequency and α = g/4π. Invited talk at the Workshop on Quantum Chromodynamics, 3-8 June, 1996, American University of Paris, France. Laboratoire de la Direction des Sciences de la Matière du Commissariat à l’Energie Atomique THE QUASIPARTICLE STRUCTURE OF HOT GAUGE THEORIES Edmond IANCU Service de Physique Théorique b , CE-Saclay, 91191 Gif-sur-Yvette, France The study of the ultrarelativistic plasmas in perturbation theory is plagued with infrared divergences which are not eliminated by the screening corrections. They affect, in particular, the computation of the lifetime of the elementary excitations, thus casting doubt on the validity of the quasiparticle picture. We show that, for Abelian plasmas at least, the infrared problem of the damping rate can be solved by a non-perturbative treatment based on the Bloch-Nordsieck approximation. The resulting expression of the fermion propagator is free of divergences, and exhibits a non-exponential damping at large times: SR(t) ∼ exp{−αTt lnωpt}, where ωp = gT/3 is the plasma frequency and α = g/4π.