Anisotropically Inflating Universes

TL;DR

This paper demonstrates that in certain higher-order gravity theories, there exist anisotropically inflating vacuum solutions with positive cosmological constant, challenging the universality of the cosmic no-hair theorem.

Contribution

It provides exact anisotropic inflation solutions in quadratic curvature gravity theories, showing deviations from de Sitter behavior not present in general relativity.

Findings

Existence of anisotropic inflationary solutions in quadratic gravity

Deviation from de Sitter universe in these models

Implications for early universe inflation and gravitational thermodynamics

Abstract

We show that in theories of gravity that add quadratic curvature invariants to the Einstein-Hilbert action there exist expanding vacuum cosmologies with positive cosmological constant which do not approach the de Sitter universe. Exact solutions are found which inflate anisotropically. This behaviour is driven by the Ricci curvature invariant and has no counterpart in the general relativistic limit. These examples show that the cosmic no-hair theorem does not hold in these higher-order extensions of general relativity and raises new questions about the ubiquity of inflation in the very early universe and the thermodynamics of gravitational fields.