  Early universe equations of state including realistic interactions between
constituents are built up. Under certain reasonable assumptions, these
equations are able to generate an inflationary regime prior to the
nucleosynthesis period. The resulting accelerated expansion is intense enough
to solve the flatness and horizon problems. In the cases of curvature parameter
\kappa equal to 0 or +1, the model is able to avoid the initial singularity and
offers a natural explanation for why the universe is in expansion.
