Fluid phonons, protoinflationary dynamics and large-scale gravitational fluctuations

TL;DR

This paper investigates the properties of fluid phonons at the start of inflation, deriving new constraints on their temperature and sound speed based on gravitational fluctuations and tensor-to-scalar ratio measurements.

Contribution

It introduces a novel analysis linking fluid phonon dynamics with inflationary parameters, providing constraints on sound speed and temperature before inflation begins.

Findings

Constraints on phonon sound speed and temperature derived from inflationary parameters.

Relation between Hubble radius size and inflationary horizon redshifted to present.

Potential to measure phonon sound speed from tensor-to-scalar ratio and spectral index.

Abstract

We explore what can be said on the effective temperature and sound speed of a statistical ensemble of fluid phonons present at the onset of a conventional inflationary phase. The phonons are the actual normal modes of the gravitating and irrotational fluid that dominates the protoinflationary dynamics. The bounds on the tensor to scalar ratio result in a class of novel constraints involving the slow roll parameter, the sound speed of the phonons and the temperature of the plasma prior to the onset of inflation. If the current size of the Hubble radius coincides with the inflationary event horizon redshifted down to the present epoch, the sound speed of the phonons can be assessed from independent measurements of the tensor to scalar ratio and of the tensor spectral index.