The minimal curvaton-higgs model

We present the first full study of the minimal curvaton-higgs (MCH) model, which is a minimal interpretation of the curvaton scenario with one real scalar coupled to the standard model Higgs boson. The standard model coupling allows the dynamics of the model to be determined in detail, including effects from the thermal background and from radiative corrections to the potential. The relevant mechanisms for curvaton decay are incomplete non-perturbative decay (delayed by thermal blocking), followed by decay via a dimension-5 non-renormalisable operator. To avoid spoiling the predictions of big bang nucleosynthesis, we find the "bare" curvaton mass to be m_\sigma > 8 x 10^4 GeV. To match observational data from Planck there is an upper limit on the curvaton-higgs coupling g, between 10^-3 and 10^-2, depending on the mass. This is due to interactions with the thermal background. We find that typically non-Gaussianities are small but that if fnl is observed in the near future then m_\sigma < 5 x 10^9 GeV, depending on Hubble scale during inflation. In a thermal dark matter model, the lower bound on m_\sigma\ can increase substantially. The parameter space may also be affected once the baryogenesis mechanism is specified.