Flows into de Sitter space from anisotropic initial conditions: An effective field theory approach

TL;DR

This paper develops an effective field theory framework to analyze how anisotropic homogeneous spacetimes evolve towards isotropic de Sitter states, even without a cosmological constant or energy conditions, revealing new pathways to cosmic isotropization.

Contribution

It introduces a general EFT approach for single-clock systems in anisotropic spacetimes, identifying conditions under which flows to de Sitter occur beyond Wald's theorem.

Findings

Flows to de Sitter can happen without a bare cosmological constant.

Anisotropic spacetimes can isotropize under broader conditions than previously known.

Effective cosmological constant emerges dynamically in these flows.

Abstract

For decades, physicists have analyzed various versions of a ``cosmic no-hair" conjecture, to understand under what conditions a spacetime that is initially spatially anisotropic and/or inhomogeneous will flow into an isotropic and homogeneous state. Wald's theorem, in particular, established that homogeneous but anisotropic spacetimes, if filled with a positive cosmological constant plus additional matter sources that satisfy specific energy conditions, will necessarily flow toward an (isotropic) de Sitter state at late times. In this paper we study the flow of homogeneous but anisotropic spacetimes toward isotropic states under conditions more general than those to which Wald's theorem applies. We construct an effective field theory (EFT) treatment for generic ``single-clock" systems in anisotropic spacetimes -- which are not limited to realizations compatible with scalar-field constructions -- and identify fixed points in the resulting phase space. We identify regions of this phase space that flow to isotropic fixed points -- including a de Sitter fixed point -- even in the absence of a bare cosmological constant, and for matter sources that do not obey the energy conditions required for Wald's theorem. Such flows into de Sitter reveal the emergence of an effective cosmological constant.