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

• Published in: Annalen der Physik Vol. 534; no. 8
• Main Author: Oikonomou, Vasilis K.
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01-08-2022
• Subjects: BBO; Deceleration; DECIGO; Energy spectra; Equations of state; Gravitational waves; inflationary gravitational waves; LISA; modified gravity; Parameters; primordial gravitational waves; Synergistic effect
• ISSN: 0003-3804; 1521-3889
• DOI: 10.1002/andp.202200134

In 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 f(R)$f(R)$ gravity and of radiation and matter perfect fluids shall be considered. Two cases of interest shall be studied, one with equation of state parameter w=−1/3$w=-1/3$, in which case the Universe neither accelerates nor decelerates, and one with w=0$w=0$ 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 w=−1/3$w=-1/3$ and w=0$w=0$ cases, the energy spectrum of the primordial gravitational waves is amplified, but for the w=0$w=0$ case, the effect is stronger.
This paper studies the effects of non standard post inflationary cosmologies, realized by modified gravity in the presence of matter and radiation perfect fluids.