Gravitational self-interactions of a degenerate quantum scalar field

TL;DR

This paper introduces a formalism to quantify quantum deviations from classical field equations, revealing how quantum effects cause condensates to deplete over finite timescales, challenging classical descriptions.

Contribution

It develops a new formalism to calculate quantum departures from classical field equations and applies it to self-gravitating and contact-interacting condensates.

Findings

Quantum effects induce pair jumps out of condensates.

Homogeneous condensates have longer classicality duration.

Inhomogeneous condensates deplete faster.

Abstract

We develop a formalism to help calculate in quantum field theory the departures from the description of a system by classical field equations. We apply the formalism to a homogeneous condensate with attractive contact interactions and to a homogeneous self-gravitating condensate in critical expansion. In their classical descriptions, such condensates persist forever. We show that in their quantum description, parametric resonance causes quanta to jump in pairs out of the condensate into all modes with wavector less than some critical value. We calculate in each case the time scale over which the homogeneous condensate is depleted, and after which a classical description is invalid. We argue that the duration of classicality of inhomogeneous condensates is shorter than that of homogeneous condensates.