Isocurvature perturbations in extra radiation

Understand

Recent cosmological observations, including measurements of the CMB anisotropy and the primordial helium abundance, indicate the existence of an extra radiation component in the Universe beyond the standard three neutrino species.

• In this paper we explore the possibility that the extra radiation has isocurvatrue fluctuations.
• A general formalism to evaluate isocurvature perturbations in the extra radiation is provided in the mixed inflaton-curvaton system, where the extra radiation is produced by the decay of both scalar fields.
• We also derive constraints on the abundance of the extra radiation and the amount of its isocurvature perturbation.