Singularity avoidance in rainbow cosmology

Abstract

It has been recently claimed that the initial singularity might be avoided in the context of rainbow cosmology, where one attempts to account for quantum-gravitational corrections through an effective-theory description based on an energy-dependent ("rainbow") space-time metric. We analyse this picture in detail in an attempt to present a more rigorous description of the problem. In particular, we show that the implications of a rainbow metric for thermodynamics are more significant than previously appreciated. We show two particularly meaningful examples where the singularity is not avoided suggesting that, although the rainbow-metric scenario provides tantalizing hints of singularity avoidance, it is inconclusive since some key questions remain to be addressed just when the scale factor is very small, a regime which, as here argued, cannot be reliably described by an effective rainbow-metric picture.