Observational constraints of the Gravitational Waves in the Brans-Dicke Theory

TL;DR

This paper explores how primordial gravitational waves in Brans-Dicke theory compare to General Relativity, focusing on quantum origins, observable spectra, and the influence of the coupling parameter .

Contribution

It provides a detailed analysis of gravitational wave observables in Brans-Dicke theory and compares them with General Relativity, highlighting the role of the coupling parameter .

Findings

Results for particle number, power spectrum, and energy density are similar in both theories when <10.

Spectral index approaches GR predictions when >1.

The coupling parameter  may vary with cosmological scale.

Abstract

We investigate the quantum origin of the primordial cosmological gravitational waves in the Brans-Dicke theory. We compute the number of gravitons $N_k$ produced during inflation and the observables: power spectrum $P_T$, spectral index $n_T$ and energy density $\Omega_k$. By comparison with General Relativity we see that the results for both theories are the same for the case of the particles number $N_k$ and for the case of the power spectrum $P_T$ and the energy density $\Omega$ only when $\omega<10$. For the spectral index $n_T$ we found that when the Brans-Dicke coupling parameter $\omega$ is bigger than unity the spectral index approximates the expression found in the General Relativity. This may awake us to the possibility that $\omega$ varies with the cosmological scale.