Squeezed Thermal Vacuum and the Maximum Scale for Inflation

TL;DR

This paper investigates how stimulated graviton emission from a thermal initial state affects inflation scale constraints, showing that the inflation scale must be lowered to match observed CMB anisotropies due to enhanced low-energy graviton production.

Contribution

It introduces the impact of thermal initial states on graviton emission, providing new constraints on inflation scale based on stimulated emission effects.

Findings

Low-energy graviton spectrum is enhanced by stimulated emission.

Inflation scale must be lowered to avoid exceeding CMB quadrupole anisotropy.

Thermal initial conditions significantly influence gravitational wave spectra.

Abstract

We consider the stimulated emission of gravitons from an initial state of thermal equilibrium, under the action of the cosmic gravitational background field. We find that the low-energy graviton spectrum is enhanced if compared with spontaneous creation from the vacuum; as a consequence, the scale of inflation must be lowered, in order not to exceed the observed CMB quadrupole anisotropy. This effect is particularly important for models based on a symmetry-breaking transition which require, as initial condition, a state of thermal equilibrium at temperatures of the order of the inflation scale.