F(R)$f(R)$‐Gravity Generated Post‐Inflationary Eras and Their Effect on Primordial Gravitational Waves

Abstract

AbstractIn this work the effects of a geometrically generated post‐inflationary era on the energy spectrum of the primordial gravitational waves are considered. Specifically, a post‐inflationary constant equation of state era, generated by the synergistic effect of gravity and of radiation and matter perfect fluids shall be considered. Two cases of interest shall be studied, one with equation of state parameter , in which case the Universe neither accelerates nor decelerates, and one with so an early matter domination era. For the evaluation of the inflationary observational indices which is relevant for the calculation of the gravitational waves energy spectrum, the effects of the constant equation of state parameter era, on the e‐foldings number is also taken into account. In both the and cases, the energy spectrum of the primordial gravitational waves is amplified, but for the case, the effect is stronger.