Dirac spinors in Bianchi-I f(R)-cosmology with torsion

TL;DR

This paper investigates how Dirac spinors influence the evolution of Bianchi-I cosmological models within torsional $f(R)$-gravity, highlighting conditions for physical viability, singularity avoidance, and well-posed initial value problems.

Contribution

It analyzes the impact of different $f(R)$ functions on universe isotropization, singularity avoidance, and the initial value problem in torsional $f(R)$-gravity with Dirac spinors.

Findings

Some $f(R)$ models do not isotropize or have Einstein limits.

Torsion can prevent cosmological singularities.

The initial value problem is well-posed due to conservation laws.

Abstract

We study Dirac spinors in Bianchi type-I cosmological models, within the framework of torsional $f(R)$-gravity. We find four types of results: the resulting dynamic behavior of the universe depends on the particular choice of function $f(R)$; some $f(R)$ models do not isotropize and have no Einstein limit, so that they have no physical significance, whereas for other $f(R)$ models isotropization and Einsteinization occur, and so they are physically acceptable, suggesting that phenomenological arguments may select $f(R)$ models that are physically meaningful; the singularity problem can be avoided, due to the presence of torsion; the general conservation laws holding for $f(R)$-gravity with torsion ensure the preservation of the Hamiltonian constraint, so proving that the initial value problem is well-formulated for these models.