General Relativity as an Attractor in Scalar-Tensor Stochastic Inflation

TL;DR

This paper demonstrates that in scalar-tensor inflation models, quantum fluctuations lead to a probability distribution that favors general relativity as an attractor, with the Planck mass stabilizing at large values.

Contribution

It shows that variable Brans-Dicke parameter models have stationary distributions favoring general relativity, unlike constant parameter models which run away to infinity.

Findings

Stationary probability distributions exist with finite Planck mass.

General relativity emerges as an attractor during quantum diffusion.

Models with variable $ta$ avoid runaway solutions.

Abstract

Quantum fluctuations of scalar fields during inflation could determine the very large-scale structure of the universe. In the case of general scalar-tensor gravity theories these fluctuations lead to the diffusion of fundamental constants like the Planck mass and the effective Brans--Dicke parameter, $\omega$. In the particular case of Brans--Dicke gravity, where $\omega$ is constant, this leads to runaway solutions with infinitely large values of the Planck mass. However, in a theory with variable $\omega$ we find stationary probability distributions with a finite value of the Planck mass peaked at exponentially large values of $\omega$ after inflation. We conclude that general relativity is an attractor during the quantum diffusion of the fields.