Transport coefficients in the early universe

Abstract

We calculate numerically the electrical conductivity $\sigma$, heat conductivity $\kappa$ and shear viscosity $\eta$ of the hot plasma present in the early universe for the temperature interval $1\MeV\lsim T\lsim 10\GeV$. We use the Boltzmann collision equation to compute all the scattering matrix elements and regulate them by the thermal masses of the $t$- and $u$-channel particles. No leading order approximation is needed because of the numerical integration routines used.