Soft gravitons as Goldstone modes of spontaneously broken asymptotic symmetries in de Sitter spacetimes

TL;DR

This paper shows that soft graviton modes in de Sitter space are Goldstone modes resulting from spontaneously broken asymptotic symmetries, affecting local measurements and the global vacuum structure.

Contribution

It identifies soft gravitons as Goldstone modes of broken asymptotic symmetries in de Sitter space and analyzes their implications for local measurements and vacuum states.

Findings

Soft gravitons are Goldstone modes of broken asymptotic symmetries.

Local measurements collapse the symmetric state to the broken state.

A small region evolves into a broken phase after the Page time.

Abstract

I demonstrate that soft graviton modes in de Sitter spacetimes are the Goldstone modes of the spontaneously broken asymptotic symmetry group of de Sitter space. I then show that any local measurement, including the effects of the environment, will collapse the symmetric state onto the broken state in the large volume limit. In any discussion involving observers, de Sitter spacetimes are, therefore, best described globally by the broken phase, while local observers, in the small volume limit, can not discriminate between different degenerate global vacuum states and are therefore best described by the symmetric state. As a consequence, a small Hubble-sized local region initially in the symmetric state will, after a time scale corresponding to the Page time of de Sitter space, have expanded to a large region in the broken state. This illuminates the physical nature of soft graviton modes in de Sitter spacetimes.