An effective theory for hot non-Abelian dynamics

I try to explain some recent progress in understanding the non-perturbative dynamics of hot non-Abelian gauge theories. The non-perturbative physics is due to soft spatial momenta $|\vec{p}|\sim g^2 T$ where $g$ is the gauge coupling and $T$ is the temperature. An effective theory for the soft field modes is obtained by integrating out the field modes with momenta of order $T$ and of order $g T$ in a leading logarithmic approximation. In this effective theory the time evolution of the soft fields is determined by a local Langevin-type equation. This effective theory determines the parametric form of the rate for hot electroweak baryon number violation as $\Gamma = \kappa g^{10} \log(1/g) T^4$. The non-perturbative coefficient $\kappa$ is independent of the gauge coupling and it can be computed by solving the effective equations of motion on a lattice.