we obtain a *stiff dominated* (SD) period with EoS ${\mkern 1.5mu\overline{\mkern-1.5muw\mkern-1.5mu}\mkern 1.5mu} > 1/3$.

In general the effective EoS in the epoch following immediately after inflation must fall in the range [$-1/3 < {\mkern 1.5mu\overline{\mkern-1.5muw\mkern-1.5mu}\mkern 1.5mu} < 1$]{}. Even though it is common to assume that [$0 \leq \bar w \leq 1/3$]{}, there is $a~priori$ no reason (theoretical or observational) to exclude the [*stiff*]{} case [$1/3 < {\mkern 1.5mu\overline{\mkern-1.5muw\mkern-1.5mu}\mkern 1.5mu} < 1$]{}. In this paper we are particularly interested in exploring this latter possibility. In fact, a post-inflationary period with a stiff EoS can be realized easily in a generic model of inflation. For example, in scalar singlet driven inflation, the slow-roll condition is achieved by simply demanding [$V \gg K$]{}, where [$V$]{} and [$K$]{} are the inflaton potential and kinetic energy densities. Inflation cannot be sustained however if the potential drops to [$V < K/2$]{}. Furthermore, if a feature in the inflaton potential allows its value [$V$]{} to drop much below the kinetic energy [$K$]{}, the EoS can become stiff after inflation, [$w = (K-V)/(K+V) > 1/3$]{}.

A simple realization of an SD regime is obtained by assuming a rapid transition of the potential from [$V \gg K$]{} during 