Modular inflation and the orthogonal axion as curvaton

We study a particular supersymmetric realization of the Peccei-Quinn symmetry which provides a suitable candidate for the curvaton field. The class of models considered also solves the mu problem, while generating the Peccei-Quinn scale dynamically. The curvaton candidate is a pseudo Nambu-Goldstone boson corresponding to an angular degree of freedom orthogonal to the axion field. Its order parameter increases substantially following a phase transition during inflation. This results in a drastic amplification of the curvaton perturbations. Consequently, the mechanism is able to accommodate low-scale inflation with Hubble parameter at the TeV scale. Hence, we investigate modular inflation using a string axion field as the inflaton with inflation scale determined by gravity mediated soft supersymmetry breaking. We find that modular inflation with the orthogonal axion as curvaton can indeed account for the observations for natural values of the parameters.