Initial Conditions for Inflation

TL;DR

This paper examines the physical viability of various de Sitter-invariant states for scalar fields, concluding that only the thermal vacuum remains physical when gravity is considered, impacting initial conditions for inflation.

Contribution

It demonstrates that all de Sitter-invariant states except the thermal vacuum are unphysical with gravity, highlighting the need for fine-tuning in inflation initial conditions.

Findings

Only the thermal vacuum is physical with gravity.

Other invariant states require fine-tuning for observable effects.

Implications for initial conditions in inflation models.

Abstract

Free scalar fields in de Sitter space have a one-parameter family of states invariant under the de Sitter group, including the standard thermal vacuum. We show that, except for the thermal vacuum, these states are unphysical when gravitational interactions are included. We apply these observations to the quantum state of the inflaton, and find that, at best, dramatic fine tuning is required for states other than the thermal vacuum to lead to observable features in the CMBR anisotropy.