# $q$-deformed 3D Loop Gravity on the Torus

## TL;DR

This paper develops a $q$-deformed loop gravity framework for the 2-torus, linking it to Chern-Simons theory and the combinatorial quantization approach, providing explicit phase space and symmetry descriptions.

## Contribution

It explicitly constructs the $q$-deformed gauge symmetries and phase space for the 2-torus, connecting loop quantum gravity with Chern-Simons quantization methods.

## Key findings

- Derived the reduced physical phase space of Dirac observables.
- Linked $q$-deformed loop gravity to the Fock-Rosly bracket and combinatorial quantization.
- Reformulated the phase space for zero cosmological constant using Poincaré holonomies.

## Abstract

The $q$-deformed loop gravity framework was introduced as a canonical formalism for the Turaev-Viro model (with $\Lambda < 0$), allowing to quantize 3D Euclidean gravity with a (negative) cosmological constant using a quantum deformation of the gauge group. We describe its application to the 2-torus, explicitly writing the $q$-deformed gauge symmetries and deriving the reduced physical phase space of Dirac observables, which leads back to the Goldman brackets for the moduli space of flat connections. Furthermore it turns out that the $q$-deformed loop gravity can be derived through a gauge fixing from the Fock-Rosly bracket, which provides an explicit link between loop quantum gravity (for $q$ real) and the combinatorial quantization of 3d gravity as a Chern-Simons theory with non-vanishing cosmological constant $\Lambda<0$. A side-product is the reformulation of the loop quantum gravity phase space for vanishing cosmological constant $\Lambda=0$, based on $\mathrm{SU}(2)$ holonomies and $\mathfrak{su}(2)$ fluxes, in terms of $\mathrm{ISU}(2)$ Poincar\'e holonomies. Although we focus on the case of the torus as an example, our results outline the general equivalence between 3D $q$-deformed loop quantum gravity and the combinatorial quantization of Chern-Simons theory for arbitrary graph and topology.