Stochastic Background of Relic Scalar Gravitational Waves tuned by Extended Gravity

TL;DR

This paper investigates the spectrum of relic scalar gravitational waves in scalar-tensor and $f(R)$ gravity theories, analyzing their production, spectrum, and compatibility with Solar System and cosmological constraints.

Contribution

It demonstrates that certain $f(R)$ gravity models produce relic scalar gravitational waves consistent with local and cosmological tests, advancing alternative theories of gravity.

Findings

Viable $f(R)$ models satisfy Solar System tests.

Scalar gravitational wave spectrum is consistent with observational bounds.

Models can explain cosmic acceleration without a cosmological constant.

Abstract

A stochastic background of relic gravitational waves is achieved by the so called adiabatically-amplified zero-point fluctuations process derived from early inflation. It provides a distinctive spectrum of relic gravitational waves. In the framework of scalar-tensor gravity, we discuss the scalar modes of gravitational waves and the primordial production of this scalar component which is generated beside tensorial one. Then we analyze different viable $f(R)$-gravities towards the Solar System tests and stochastic gravitational waves background. The aim is to achive experimental bounds for the theory at local and cosmological scales in order to select models capable of addressing the accelerating cosmological expansion without cosmological constant but evading the weak field constraints. It is demonstrated that viable $f(R)$-gravities under consideration not only satisfy the local tests, but additionally, pass the PPN-and stochastic gravitational waves bounds for large classes of parameters.