A solution of the strong CP problem via the Peccei-Quinn mechanism through the Nieh-Yan modified gravity and cosmological implications

TL;DR

This paper proposes a novel solution to the strong CP problem by linking the Barbero-Immirzi field with the QCD axion within a modified gravity framework, predicting specific cosmological and observational consequences.

Contribution

It introduces a new model connecting the Barbero-Immirzi field to the QCD axion, predicting the Peccei-Quinn symmetry breaking scale and implications for dark matter and gravitational waves.

Findings

Predicts a specific Peccei-Quinn symmetry breaking scale.

Provides bounds on the tensor-to-scalar ratio from primordial gravitational waves.

Evaluates the axion's contribution to dark matter.

Abstract

By identifying the recently introduced Barbero-Immirzi field with the QCD axion, the strong CP problem can be solved through the Peccei-Quinn mechanism. A specific energy scale for the Peccei-Quinn symmetry breaking is naturally predicted by this model. This provides a complete dynamical setting to evaluate the contribution of such an axion to the cold dark matter content of the Universe. Furthermore, a tight upper bound on the tensor-to-scalar ratio production of primordial gravitational waves can be fixed, representing a strong experimental test for this model.