Cosmological gravitons and the expansion dynamics during the matter age - art. no. 123510

Extending previous results [Phys. Rev. D 56, 6351 (1997)], we estimate the back reaction of cosmological,gravitons in expansion dynamics, during the m atter age. Tensor perturbations with scales larger than the Hubble radius a re created due to the inequivalence of vacua at different times. During non inflationary phases these perturbations become effective gravitational wave s as they enter the Hubble radius, adding new contributions to the energy d ensity of the subhorizon waves. During the radiation epoch the creation of these effective gravitons may lead to a departure from the standard behavio r a(t)proportional to 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 inf lationary period. The dynamical equation obeyed by the scale factor is deri ved and numerically solved for different values of the relevant parameters involved. [S0556-2821(99)08420-9].