Quark era in the primeval universe

In the hadronic era of the standard cosmological model, the density can be so high as to invalidate a description in terms of hadrons: this may happen at densities as low as 1.4 times the nuclear density (depending on the quark interactions under consideration). In fact, a quark soup description is more suitable for the description of the hadronic era. In this paper, a phenomenological model - studied elsewhere - of quark matter is applied to a possible quark era in the early universe. Essentially, nothing very spectacular happens and the universe evolves as if it were radiation-dominated. However, at densities slightly above the nuclear density, a phase transition (between a phase composed of heavy quarks and a phase made of light quarks) occurs. Furthermore, the derivation of our basic equations put the emphasis on the necessity of giving up the notion of thermal equilibrium in the early universe or redefining it. (orig.)