Pachner moves in a 4d Riemannian holomorphic Spin Foam model

TL;DR

This paper analyzes a 4D Riemannian Spin Foam model using holomorphic techniques, deriving explicit behaviors under Pachner moves and exploring conditions for invariance and divergence, which are crucial for understanding quantum gravity.

Contribution

It introduces a novel holomorphic representation approach with new tools, providing the first analytic expressions for Pachner move behaviors in 4D Spin Foam models.

Findings

Invariance up to a factor for 4-2 and 5-1 moves under certain truncations.

Divergence occurs in the 5-1 move for some parameters.

Potential for recovering diffeomorphism invariance in the continuum limit.

Abstract

In this work we study a Spin Foam model for 4d Riemannian gravity, and propose a new way of imposing the simplicity constraints that uses the recently developed holomorphic representation. Using the power of the holomorphic integration techniques, and with the introduction of two new tools: the homogeneity map and the loop identity, for the first time we give the analytic expressions for the behaviour of the Spin Foam amplitudes under 4-dimensional Pachner moves. It turns out that this behaviour is controlled by an insertion of nonlocal mixing operators. In the case of the 5-1 move, the expression governing the change of the amplitude can be interpreted as a vertex renormalisation equation. We find a natural truncation scheme that allows us to get an invariance up to an overall factor for the 4-2 and 5-1 moves, but not for the 3-3 move. The study of the divergences shows that there is a range of parameter space for which the 4-2 move is finite while the 5-1 move diverges. This opens up the possibility to recover diffeomorphism invariance in the continuum limit of Spin Foam models for 4D Quantum Gravity.