On Spinfoam Models in Large Spin Regime

TL;DR

This paper analyzes the semiclassical behavior of the Lorentzian EPRL spinfoam model in the large spin regime, revealing conditions under which certain geometries dominate and deriving a curvature expansion of the effective action.

Contribution

It introduces a detailed stationary phase analysis of the large spin limit in Lorentzian spinfoam models, connecting critical configurations to low-energy effective gravity.

Findings

Critical configurations dominate when deficit angles satisfy specific bounds.

The model yields a curvature expansion with high-curvature corrections.

UV modifications of Einstein gravity appear as subleading terms.

Abstract

We study the semiclassical behavior of Lorentzian Engle-Pereira-Rovelli-Livine (EPRL) spinfoam model, by taking into account the sum over spins in the large spin regime. We also employ the method of stationary phase analysis with parameters and the so called, almost-analytic machinery, in order to find the asymptotic behavior of the contributions from all possible large spin configurations in the spinfoam model. The spins contributing the sum are written as ${J}_f=\lambda {j}_f$ where $\l$ is a large parameter resulting in an asymptotic expansion via stationary phase approximation. The analysis shows that at least for the simplicial Lorentzian geometries (as spinfoam critical configurations), they contribute the leading order approximation of spinfoam amplitude only when their deficit angles satisfy $\gamma{\Theta}_f\leq\lambda^{-1/2}$ mod $4\pi\mathbb{Z}$. Our analysis results in a curvature expansion of the semiclassical low energy effective action from the spinfoam model, where the UV modifications of Einstein gravity appear as subleading high-curvature corrections.