Electroweak-scale inflation, inflaton-Higgs mixing and the scalar spectral index

We construct a phenomenological model of electroweak-scale inflation that is in accordance with recent CMB observations by WMAP, while setting the stage for a zero-temperature electroweak transition as assumed in recent models of baryogenesis. We find that especially the scalar spectral index poses tight constraints for low-scale inflation models. The inflaton-Higgs coupling leads to substantial mixing of the scalar degrees of freedom. Two types of scalar particles emerge with decay widths similar to that of the Standard Model Higgs