Abstract
Extending previous results [Phys. Rev. D 56, 6351 (1997)], we estimate the back reaction of cosmological gravitons in expansion dynamics, during the matter age. Tensor perturbations with scales larger than the Hubble radius are created due to the inequivalence of vacua at different times. During noninflationary phases these perturbations become effective gravitational waves as they enter the Hubble radius, adding new contributions to the energy density of the subhorizon waves. During the radiation epoch the creation of these effective gravitons may lead to a departure from the standard behavior $a(t)\ensuremath{\propto}{t}^{1/2},$ with possible consequences to several cosmic processes, such as primordial nucleosynthesis. We examine the implications of this phenomenon during the matter-dominated era, assuming an initial inflationary period. The dynamical equation obeyed by the scale factor is derived and numerically solved for different values of the relevant parameters involved.
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