The Trace-Free Einstein Equations and inflation

TL;DR

This paper demonstrates that using trace-free Einstein equations, which are related to unimodular gravity, does not hinder the inflationary process in cosmology, addressing concerns about vacuum energy and inflation.

Contribution

It shows that inflation can occur normally under trace-free Einstein equations, countering previous doubts about their compatibility with inflationary dynamics.

Findings

Inflation proceeds as usual with trace-free Einstein equations.

The concern that trace-free equations prevent inflaton-driven inflation is unfounded.

Supports the viability of unimodular gravity in cosmological models.

Abstract

The trace-free version of the Einstein Gravitational equations, essentially equivalent to unimodular gravity, can solve the troubling issue of the huge discrepancy between quantum field theory estimates of the vacuum energy density and the astronomically observed value of the cosmological constant. However it has been suggested that this proposal cannot work because it prevents the inflaton potential energy from driving inflation. It is shown here that that concern is unjustified: inflation proceeds as usual if we adopt the trace free gravitational equations.