Gauge-Invariant Renormalization Group at Finite Temperature and Debye Screening

I describe an application of Wilson Renormalization group to the real time formalism of finite temperature field theory. The approach has two nice features: 1) the RG flow equations describe non-perturbatively the effect of thermal fluctuations only, and, 2) the flow is gauge invariant. I then describe the application of the method to the study of the gluon self-energy in SU(N), and present results for the computation of the Debye and magnetic screening masses.