Cosmic Lockdown: When Decoherence Saves the Universe from Tunneling

TL;DR

This paper explores how quantum decoherence in cosmological settings can suppress tunneling between vacua, effectively locking the universe into a local minimum through a quantum Zeno effect, with implications for inflationary cosmology.

Contribution

It introduces a detailed model of decoherence effects on vacuum tunneling during inflation, demonstrating how environmental interactions can stabilize false vacua via the quantum Zeno effect.

Findings

Decoherence suppresses quantum interference between vacua.

Heavy fields relax adiabatically to the true vacuum.

Light fields exhibit non-adiabatic false-vacuum occupation enhancements.

Abstract

We investigate how quantum decoherence influences the tunneling dynamics of quantum fields in cosmological spacetimes. Specifically, we study a scalar field in an asymmetric double-well potential during inflation, coupled to environmental degrees of freedom provided by a continuum of spectator fields. This setup enables a systematic derivation of both Markovian and non-Markovian master equations, along with their stochastic unravelings, which we solve numerically. We find that, while decoherence is essential for suppressing quantum interference between vacua, its impact on the relative vacuum populations is limited. Fields heavier than the Hubble scale relax adiabatically toward the true vacuum with high probability, while lighter fields exhibit non-adiabatic enhancements of false-vacuum occupation. Once the system has decohered, quantum tunneling between vacua becomes strongly suppressed, effectively locking the system into the stochastically selected local minimum. This ``cosmic lockdown'' mechanism is a manifestation of the quantum Zeno effect: environmental monitoring stabilizes enhanced false-vacuum occupation for light fields by preventing them from tunneling.