Big Bounce cosmology for Palatini $R^2$ gravity with a Nieh-Yan term

TL;DR

This paper explores a Palatini $f(R)$ gravity model with a Nieh-Yan term, revealing bouncing cosmologies, late-time universe recovery, and connections to Loop Quantum Gravity, with implications for early universe and quantum gravity phenomenology.

Contribution

It introduces a novel Palatini $f(R)$ gravity model with a Nieh-Yan term, analyzing its cosmological solutions and linking to Loop Quantum Gravity features.

Findings

Bouncing cosmological scenarios depending on the quadratic correction sign.

Recovery of standard universe dynamics at late times.

Asymptotic freezing of the Immirzi field, aligning with Loop Quantum Gravity.

Abstract

We analyze the cosmological implementation of Palatini $f(R)$ theories, constructed with a Nieh-Yan term and solved with respect to the torsion. We consider the relevant case of the quadratic correction to the Hilbert-Palatini action in the Ricci scalar, mimicking the Starobinsky model of the metric formulation. We point out the emergence of peculiar cosmological scenarios, depending on the sign of such correction, able to reproduce bouncing settings and to restore the standard Universe dynamics in the late asymptotic limit. Furthermore, we outline the settling of Little-Rip dynamics, which calls for a deeper investigation in order to be regularized via matter creation. Finally, we also show that in our model the Immirzi field is asymptotically frozen in time, resembling the morphology of Loop Quantum Gravity standard formulation.