HEP Theory Journal Club

False and real decoherence of primordial perturbations

Junsei Tokuda

McGill University

Quantum fluctuations of the metric are amplified during inflation, producing the macroscopic perturbations observed in the late universe. To clarify whether these fluctuations retain their quantum coherence, we study the decoherence of super-Hubble modes induced by gravitational nonlinearities during inflation. We show that cubic gravitational couplings, constrained by the soft theorem, lead to a UV-divergent decoherence rate at one loop, arising from violent zero-point fluctuations in the deep UV. We argue that these divergences are unobservable, as they vanish when considering time-smeared observables that better reflect realistic measurements. We then compute the finite decoherence rate induced by an excited environment, which remains robust against such smearing. This talk is based on work in preparation.