Perturbative Non-Equilibrium Thermal Field Theory

by Dr Peter Millington (Manchester)

Tuesday 29 Oct 2013, 18:00 → 19:00 Europe/Berlin

TUM Physik Department 3343 (Universe)

We present a fully perturbative approach to non-equilibrium thermal field theory, applicable to the description of ultra-relativistic many-body systems across a range of disciplines. The resulting diagrammatic perturbation series are built from non-homogeneous free propagators and explicitly time-dependent vertices, which together encode the absolute spacetime dependence of the statistical background. The perturbative expansion is free of so-called pinch singularities, without the need for resummation of finite-width effects. Thus, we do not suffer the mathematical pathologies previously thought to spoil truly perturbative treatments of non-equilibrium field theory. Arriving at a definition of particle number density that does not rely on quasi-particle Ansätze, we derive general master time evolution equations for statistical distribution functions.  Subsequently truncating these transport equations in a perturbative loopwise sense, without the need for gradient expansion, we successfully capture dynamics on all timescales, including the emergence of threshold effects. Finally, within the context of a scalar model, we show how transient early-time behaviour is dominated by non-Markovian energy-violating processes, which result from the systematic inclusion of finite-time effects.