Noncommutative gravity with self-dual variables

TL;DR

This paper develops a noncommutative gravity model with self-dual variables, introducing a doubled tetrad structure, new symmetries, and analyzing the effects of noncommutativity and its relation to bimetric theories.

Contribution

It extends Palatini-Holst gravity to noncommutative spacetime with a twist deformation, leading to a bitetrad formulation and revealing new duality symmetries.

Findings

The model exhibits new duality symmetries.

Self-dual case simplifies the dynamics significantly.

Explicit perturbative effects of noncommutativity are computed.

Abstract

We build a noncommutative extension of Palatini-Holst theory on a twist-deformed spacetime, generalizing a model that has been previously proposed by Aschieri and Castellani. The twist deformation entails an enlargement of the gauge group, and leads to the introduction of new gravitational degrees of freedom. In particular, the tetrad degrees of freedom must be doubled, thus leading to a bitetrad theory of gravity. The model is shown to exhibit new duality symmetries. The introduction of the Holst term leads to a dramatic simplification of the dynamics, which is achieved when the Barbero-Immirzi parameter takes the value $\beta=-i$, corresponding to a self-dual action. We study in detail the commutative limit of the model, focusing in particular on the role of torsion and non-metricity. The effects of spacetime noncommutativity are taken into account perturbatively, and are computed explicitly in a simple example. Connections with bimetric theories and the role of local conformal invariance in the commutative limit are also explored.