Almost-homogeneity of the universe in higher-order gravity

Abstract

In the $R+\alpha R^2$ gravity theory, we show that if freely propagating massless particles have an almost isotropic distribution, then the spacetime is almost Friedmann-Robertson-Walker (FRW). This extends the result proved recently in general relativity ($\alpha =0$), which is applicable to the microwave background after photon decoupling. The higher-order result is in principle applicable to a massless species that decouples in the early universe, such as a relic graviton background. Any future observations that show small anisotropies in such a background would imply that the geometry of the early universe were almost FRW.

14 pages LaTeX, no figures; to appear in General Relativity and Gravitation

Cited by in corpus (2)

• f(R) Theories Of Gravity
• Kinematics and Dynamics of $f(R)$ Theories of Gravity