Gauge invariant coupling of fields to torsion: a string inspired model

TL;DR

This paper explores the coupling of various gauge fields to spacetime torsion inspired by string theory, analyzing their astrophysical and cosmological implications, and discusses potential roles in loop quantum gravity.

Contribution

It introduces a new class of gauge field interactions with torsion, extending string-inspired models and examining their astrophysical and quantum gravity relevance.

Findings

Predicts polarization rotation effects for electromagnetic and gravitational waves.

Proposes new gauge-torsion coupling mechanisms with astrophysical implications.

Discusses the role of a dynamic Barbero-Immirzi parameter in loop quantum gravity.

Abstract

In a consistent heterotic string theory, the Kalb-Ramond field, which is the source of spacetime torsion, is augmented by Yang-Mills and gravitational Chern-Simons terms. When compactified to 4-dimensions and in the field theory limit, such additional terms give rise to interactions with interesting astrophysical predictions like rotation of plane of polarization for electromagnetic and gravitational waves. On the other hand, if one is also interested in coupling 2 or 3-form (Abelian or non-Abelian) gauge fields to torsion, one needs another class of interaction. In this paper, we shall study this interaction and offer some astrophysical and cosmological predictions. We also comment on the possibility of such terms in loop quantum gravity where, if the Barbero-Immirzi parameter is promoted to a field, acts as a source for torsion.