Speaker
Description
In this talk, I will present a spatially flat Lorentzian cosmological subsector of (effective) spin foams and show first steps towards computing its path integral and a continuous time limit.
I will begin by introducing the classical theory in Lorentzian Regge calculus, where we discuss the classical discrete equations of motion and their solutions, coupling (massless) scalar fields, causality violations, symmetries of the action and a continuum limit.
We go to the path integral in two steps: first we review lessons learned from a (2+1)d model, whose amplitudes are motivated by the asymptotic analysis of a Lorentzian spin foam model. Then we go to (3+1)d effective spin foams and present how to efficiently evaluate the path integral using acceleration operators. Furthermore, we show under which conditions classical physics are recovered and show first indications for bouncing cosmologies.
We close with an overview of open questions and the relation to the full spin foam theory.
This talk is based on works with Alexander Jercher and José Simão.
