Fermionic Dispersion Relations in the Standard Model at Finite Temperature

We compute the one-loop dispersion relations at finite temperature for quarks, charged leptons and neutrinos in the Minimal Standard Model. The dispersion relations are calculated in two different plasma situations: for a vacuum expectation value $\upsilon$ of the Higgs field $\upsilon \neq 0$ (broken electroweak symmetry) and for $\upsilon=0$ (unbroken electroweak symmetry). The flavour and chiral non-degeneracy of the quasi-particle spectrum is studied. Numerical results show that the thermal effective masses for fermions in the broken phase have a smaller value than those in the unbroken phase. The temperature dependence of the top quark and electron neutrino thermal effective masses is also presented. Gauge invariance of one-loop dispersion relations is studied.