Abstract
Recent elaborated by T. Harko and collaborators, the $f(R,T)$ theories of gravity contemplate an optimistic alternative to dark energy, for which $R$ and $T$ stand for the Ricci scalar and the trace of the energy-momentum tensor, respectively. Although the literature has shown that the $T$ dependence on the gravitational part of the action - which is due to the consideration of quantum effects - may induce some novel features in the scope of late-time cosmological dynamics, in the radiation-dominated universe, when $T=0$, no contributions seem to rise from such theories. Apparently, $f(R,T)$ contributions to a radiation-dominated universe may rise only from the $f(R,T^\varphi)$ approach, which is nothing but the $f(R,T)$ gravity in the case of a self-interacting scalar field whose trace of the energy-momentum tensor is $T^\varphi$. We intend, in this article, to show how $f(R,T^\varphi)$ theories of gravity can contribute to the study of the primordial stages of the universe. Our results predict a graceful exit from inflationary stage to a radiation-dominated era. They also predict a late-time cosmic acceleration after a matter-dominated phase, making the $f(R,T^\varphi)$ theories able to describe, in a self-consistent way, all the different stages of the universe dynamics.
Highlights
Plenty of efforts have been made in the theoretical framework with the purpose of explaining the accelerated regime our universe has passed through a fraction of a second after the Big Bang, named the “inflationary era”
The late-time acceleration of the universe expansion [13,14,15] has been broadly investigated in such a theory of gravity [16,17,18,19,20,21,22,23,24,25], the inflationary era still presents a lack of examination
We have obtained from the first-order formalism applied to f (R, T φ) gravity two models able to describe all the different dynamical stages of the universe, from inflation, to radiation, to matter and dark-energy dominated
Summary
Plenty of efforts have been made in the theoretical framework with the purpose of explaining the accelerated regime our universe has passed through a fraction of a second after the Big Bang, named the “inflationary era”. A priori, it seems reasonable to affirm that the f (R, T ) gravity does not contribute to the study of the radiationdominated universe, since the contribution coming from the trace of the energy-momentum tensor in f (R, T ) vanishes at this stage. Such a shortcoming or incompleteness has attracted attention recently [23,24,25,26].
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