Erlangen 2026 – scientific programme

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GR: Fachverband Gravitation, Relativistische Astrophysik und Kosmologie

GR 15: Quantum Gravity and Quantum Cosmology II

GR 15.1: Talk

Thursday, March 19, 2026, 16:15–16:30, KH 02.012

Lorentzian Cosmological path integrals in effective spin foams — •Sebastian Steinhaus and Alexander Jercher — Friedrich-Schiller Universität Jena, Theoretisch-Physikalisches Institut, Jena, Germany

Spin foam models, also called covariant loop quantum gravity, are a non-perturbative, Lorentzian path integral approach to quantum gravity. Its expressions are regularised by replacing the continuous manifold by a triangulation, where the sum over geometries is encoded in group-theoretic area and angle variables. However, making contact back with classical, continuum gravity is challenging. In this talk, I will address this question in cosmology from two directions. First, I will solve the discrete (transcendental) equations of motion of cosmological models in Regge calculus and showcase how to relate them to continuum cosmology. Second, I translate this into an oscillatory Lorentzian path integral with effective spin foams and evaluate it numerically, e.g. using acceleration operators. I will discuss under which conditions classical physics (in terms of expectation values of observables) can be recovered and give an outlook to non-classical transitions, e.g. bouncing cosmologies.

Keywords: Quantum Gravity; Spin Foam Models; Regge Calculus; Numerical Methods; Quantum Cosmology