Dark radiation in LARGE volume models

Abstract

We consider reheating driven by volume modulus decays in the LARGE volume scenario. Such reheating always generates nonzero dark radiation through the decays to the axion partner, while the only competitive visible sector decays are Higgs pairs via the Giudice-Masiero term. In the framework of sequestered models where the cosmological moduli problem is absent, the simplest model with a shift-symmetric Higgs sector generates $1.56\ensuremath{\le}\ensuremath{\Delta}{N}_{\mathrm{eff}}\ensuremath{\le}1.74$. For more general cases, the known experimental bounds on $\ensuremath{\Delta}{N}_{\mathrm{eff}}$ strongly constrain the parameters and matter content of the models.