Fermion fields in Einstein-Cartan theory and the accelerated-decelerated transition in a primordial Universe

TL;DR

This paper explores how fermion fields within Einstein-Cartan theory can drive the transition from accelerated to decelerated expansion in the early Universe, highlighting the role of fermion spin and mass.

Contribution

It introduces a model where fermion spin induces acceleration and fermion mass causes deceleration, explaining the primordial Universe's transition.

Findings

Fermion spin acts as an inflaton causing acceleration.

Fermion mass leads to deceleration.

Transition between accelerated and decelerated phases is characterized by fermion properties.

Abstract

In this work the accelerated-decelerated transition in a primordial Universe is investigated by using the dynamics of fermion fields within the context of Einstein-Cartan theory, where apart from the curvature the space-time is also described by a torsion field. The model analyzed here has only a fermion field as the source of the gravitational field. The term associated with the spin of the fermion field plays the role of the inflaton which contributes to an accelerated regime whereas the one related to the fermion mass behaves as a matter field and is the responsible for a decelerated regime. Hence, by taking into account the spin of a massive fermion field it is possible to characterize the transition from the accelerated to the decelerated periods of the primordial Universe.