Interacting Constituents in Cosmology

TL;DR

This paper highlights the significance of particle interactions in cosmological models and proposes a systematic method, inspired by statistical mechanics, to incorporate these effects, demonstrating their potential impact through a toy model.

Contribution

It introduces a novel approach to include interaction terms in cosmological equations of state using statistical mechanics, addressing a previously neglected aspect.

Findings

Interaction terms can significantly influence universe evolution.

A systematic method for including interactions is proposed.

Toy model shows notable cosmological effects from interactions.

Abstract

Universe evolution, as described by Friedmann's equations, is determined by source terms fixed by the choice of pressure $\times$ energy-density equations of state $p(\rho)$. The usual approach in Cosmology considers equations of state accounting only for kinematic terms, ignoring the contribution from the interactions between the particles constituting the source fluid. In this work the importance of these neglected terms is emphasized. A systematic method, based on the Statistical Mechanics of real fluids, is proposed to include them. A toy-model is presented which shows how such interaction terms can engender significant cosmological effects.