Inflation from a nonlinear magnetic monopole field nonminimally coupled to curvature

TL;DR

This paper explores how a nonlinear magnetic monopole field nonminimally coupled to curvature can drive early universe inflation, with results consistent with recent gravitational wave and cosmological observations.

Contribution

It introduces a simple nonminimal coupling model with a nonlinear magnetic monopole field that explains early inflation and aligns with observational data.

Findings

Existence of an exponential inflationary phase

Constraints on nonminimal coupling parameters from Planck data

Compatibility with gravitational wave observations

Abstract

In the context of nonminimally coupled $f(R)$ gravity theories, we study early inflation driven by a nonlinear monopole magnetic field which is nonminimally coupled to curvature. In order to isolate the effects of the nonminimal coupling between matter and curvature we assume the pure gravitational sector to have the Einstein-Hilbert form. Thus, we study the most simple model with a nonminimal coupling function which is linear in the Ricci scalar. From an effective fluid description, we show the existence of an early exponential expansion regime of the Universe, followed by a transition to a radiation-dominated era. In particular, by applying the most recent results of the Planck collaboration we set the limits on the parameter of the nonminimal coupling, and the quotient of the nonminimal coupling and the nonlinear monopole magnetic scales. We found that these parameters must take large values in order to satisfy the observational constraints. Furthermore, by obtaining the relation for the graviton mass, we show the consistency of our results with the recent gravitational wave data GW$170817$ of LIGO and Virgo.