Primary thermalisation mechanism of Early Universe observed from Faraday-wave scattering on liquid-liquid interfaces

TL;DR

This paper uses a two-fluid interface experiment to simulate early Universe preheating, revealing how nonlinear wave scattering broadens resonance bands and triggers secondary instabilities, mirroring cosmological thermalisation processes.

Contribution

It introduces a hydrodynamical analogue model for early Universe preheating, analyzing nonlinear Faraday wave scattering and resonance broadening in a damped, interacting system.

Findings

Faraday wave scattering broadens primary resonance bands

Secondary instabilities emerge from nonlinear wave interactions

Hydrodynamical model replicates key features of cosmological preheating

Abstract

For the past two hundred years, parametric instabilities have been studied in various physical systems, such as fluids, mechanical devices and even inflationary cosmology. It was not until a few decades ago that this subharmonic unstable response arose as a central mechanism for the thermalisation of the Early Universe, in a theory known as preheating. Here we study a parametrically driven two-fluid interface to simulate the key aspects of inflationary preheating dynamics through the onset of nonlinear Faraday waves. We present a detailed analysis of the effective field theory description for interfacial waves through the factorization properties of higher-order correlations. Despite the intricacies of a damped and highly interacting hydrodynamical system, we show that the scattering of large amplitude Faraday waves is connected to a broadening of primary resonance bands and the subsequent appearance of secondary instabilities as predicted in preheating dynamics.