
Physics 2014
Cosmological backreaction in modified gravity and its implications for dark energyDOI: 10.1088/14757516/2014/09/017 Abstract: We study the effective stressenergy tensor induced by cosmological inhomogeneity in $f(R)=R+cR^2$ and equivalent scalartensor theories, motivated both by models of early universe inflation and by phenomenological alternative cosmologies to the standard $\Lambda$CDM. We use Green and Wald's framework for averaging over classical fluctuations of shortwavelength $\lambda$. By ensuring that the leading nonlinear terms from the fluctuations of the Einstein terms and the corrections both contribute in the formal limit as $\lambda\to0$, we derive a diffeomorphism invariant effective stressenergy tensor whose trace is nonvanishing and of the right sign to potentially account for the current acceleration of the universe. However a more phenomenologically acceptable dark energy model would be required if this effect were to fully account for the current acceleration.
