Inflation from a nonlinear magnetic monopole field nonminimally coupled to curvature

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 GW170817 of LIGO and Virgo.

Growth of matter overdensities in non-minimal torsion-matter coupling theories

“…These torsion-based modified gravity theories constitute a good alternative to the conventional basedcurvature modified gravity models [62]. Furthermore, in the same spirit of non-minimal f (R) gravity theories [81,82,83,84,85,86,87,88,89,90,91,92,93], one may think in an attractive generalization of this framework, by allowing a non-minimal coupling between matter and torsion [79]. This generalized theory has proven to have very important features at background level, providing an explanation for both late-time accelerated expansion, and early-time inflationary phase, that in this way, it also could lead to a possible unified description of the cosmological expansion history [80].…”

“…A very important generalization of f (T ) gravity is obtained by allowing a non-minimal coupling between torsion and matter [77,78,79,80]. This non-minimal coupling arises in a close analogy with the curvature-matter coupling in f (R) gravity [81,82,83,84,85,86,87,88,89,90,91,92,93], whose origin can have several motivations. It is well known for example that non-minimal coupling terms acting as counterterms are required when quantizing a selfinteracting scalar field in curved spacetime [94].…”

Cosmology with Variable <em>G</em> and Nonlinear Electrodynamics

“…To deal with this and other fundamental problems in modern cosmology such as the horizon problem, flatness problem, monopole problem and inflation. Magnetic universe models which portray no initial singularity due to strong electromagnetic field in the modified Nonlinear Electrodynamics (NED) can explain the cosmic inflation period of the universe which is a theory of exponential expansion of space in the early universe [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. Other models such as non-minimal coupling, varying speed of light (VSL), quantum gravity effect, Lagrange with quadratic term, inflation by scalar fields, NED without modification of general relativity have been introduced in the literature to solve the puzzle of cosmology and mystery of inflation .…”

Inflation of the universe by the non-minimal Y (R )F 2 models

“…Second is to consider a large number of vector fields in random spatial directions, and take the spatial average of the fields which was firstly proposed by Tolman and Ehrenfest [50]. The averaging procedure was applied to the non-linear electromagnetic theory in literature extensively [51][52][53][54][55][56][57]. In this procedure, it is assumed that the wavelength of the electromagnetic fields is much smaller than the space-time curvature.…”