Deformation of the EPRL spin foam model by a cosmological constant

Abstract

In this article, we consider an ad-hoc deformation of the EPRL model for quantum gravity by a cosmological constant term. This sort of deformation has been first introduced by Han for the case of the $4$-simplex. In this article, we generalise the deformation to the case of arbitrary vertices, and compute its large-$j$-asymptotics. We show that, if the boundary data corresponds to a $4d$ polyhedron $P$, then the asymptotic formula gives the usual Regge action plus a cosmological constant term. We pay particular attention to the determinant of the Hessian matrix, and show that it can be related to the one of the undeformed vertex.