Heavy physics in the CMB

Ana Achucarro, Jinn-Ouk Gong, Sjoerd Hardeman, Gonzalo Palma, Subodh Patil

Precision cosmology offers the promise of a window into quantum theories of gravity but at the moment the best theoretical predictions cannot yet match the precision expected in current and upcoming experiments. In an effective theory language, we do not understand the effect of heavy degrees of freedom well enough, for instance during inflation.

Low energy descriptions of string theory typically involve many scalar fields (the "moduli") that span a curved manifold. If some of these fields are much more massive than others, we expect them to decouple from the light modes that dominate cosmological evolution. But this assumption breaks down if the background trajectories of the light fields are not tracking geodesics in moduli space. In the case of inflation, the effect of curved trajectories on the primordial spectrum of perturbations is potentially observable in the Cosmic Microwave Background and maybe even distinguishable from other effects.