Extended thermodynamics in the early Universe.

It is a general belief that in some early stages of the evolution of the Universe unequilibrium situations played important role. In order to incorporate some deviations from thermal equilibrium into the description of the evolution, here an extension of the thermodynamic formalism is given, where, using the notion of ekaentropy, new terms are introduced into the Gibbs-Duhem relation for representing the deviation. Two situations are investigated in simplified models: the primordial thermalisation in the symmetric phase of GUT, and the development of a nonthermal distribution for massive neutrinos.