Cosmology of Cubic Poincar\'e Gauge gravity

TL;DR

This paper explores flat FLRW cosmology within a ghost-free cubic Poincaré gauge gravity framework, revealing faster expansion scenarios and potential modifications to standard cosmological models.

Contribution

It introduces a novel cubic invariant extension of Poincaré gauge gravity that remains ghost-free and explores its cosmological implications.

Findings

Faster expanding cosmologies compared to standard model

Extra degrees of freedom related to hypermomentum are dynamical in vacuum

Preliminary observational constraints are consistent with the model

Abstract

In this paper, we study flat FLRW cosmology for a Poincar\'e gauge theory containing cubic invariants that is free from ghosts in arbitrary backgrounds in the axial and vector sectors of the torsion tensor. The new degrees of freedom can be related to hypermomentum but continue to be dynamical even in vacuum. These extra degrees of freedom open a more natural way in which to construct potential gravitational models that provide possible ways to modify astrophysical and cosmological physics. In this framework, we study two particular branches of the theory where preliminary routes of exploring these new variables are exposed. The first is the branch where the hypermomentum vanishes, while the second branch involves the setting where the perfect fluid and hypermomentum parts of the sources are independently conserved. In both settings, we find generically faster expanding cosmologies with similar estimates of the cosmic matter content as in the standard model of cosmology. Cubic Poincar\'e Gauge gravity offers an interesting theoretical basis on which to study cosmology, and indicates some preliminary positive constraints when compared with observational constraints.