Relic Gravitons, Dominant Energy Condition and Bulk Viscous Stresses

TL;DR

This paper explores how bulk viscous stresses that violate the dominant energy condition can increase the frequency of relic gravitons, with implications for their detectability by future gravitational wave detectors.

Contribution

It provides a general relativistic framework showing how temporary violations of the dominant energy condition affect relic graviton spectra.

Findings

Relic graviton spectra increase in frequency during energy condition violations.

Examples demonstrate temporary violation of the dominant energy condition in cosmological models.

Implications for gravitational wave detection prospects are discussed.

Abstract

If the energy momentum tensor contains bulk viscous stresses violating the dominant energy condition (DOC) the energy spectra of the relic gravitons (produced at the time of the DOC's violation) increase in frequency in a calculable way. In a general relativistic context we give examples where the DOC is only violated for a limited amount of time after which the ordinary (radiation dominated) evolution takes place. We connect our discussion to some recent remarks of Grishchuk concerning the detectability of the stochastic gravitational wave background by the forthcoming interferometric detectors.