Peccei--Quinn mechanism in gravity and the nature of the Barbero--Immirzi parameter

Abstract

A general argument provides the motivation to consider the Barbero--Immirzi parameter as a field. The specific form of the geometrical effective action allows to relate the value of the Barbero--Immirzi parameter to other quantum ambiguities through the analog of the Peccei--Quinn mechanism.Comment: Accepted for publication on Phys. Rev. Let