The curvaton as a Bose-Einstein condensate of chiral pseudo Nambu-Goldstone bosons

Explaining cosmic inflation by the effective dynamics of an SU(NC) pure gauge theory of scale Λ∼10−6Mp is lacking an explanation of the (Gaussian) spatial curvature perturbations needed to seed the formation of large-scale structure after inflation. In this work it is demonstrated how fundamentally charged fermions of mass mF∼10−12Λ, whose approximate chiral symmetry is spontaneously broken during inflation, can cure this shortcoming. The associated gas of weakly interacting pseudo Nambu-Goldstone bosons (PNGB) undergoes Bose-Einstein (BE) condensation well before the end of inflation. This causes the occurence of condensed light scalar fields effectively acting as a curvaton. Fermions may also be charged under a gauge group G with a weak coupling g. Since fermions charged under SU(NC) are confined after inflation the decay of Nambu-Goldstone bosons, which reside in the condensates and in the PNGB radiation generated at reheating, is mainly into fermions solely charged under G. The associated decay rate Γ is estimated using PCAC and large NC counting. PNGB decay takes place during radiation domination after cosmological scales have entered the horizon. Neglecting the effects of the spontaneous breaking of G induced by the BE condensation, it is demonstrated that the observed spectrum of spatial curvature perturbations Pξ1/2∼5×10−5 is compatible with g∼10−3, a ratio rdec∼10−4 of curvaton to radiation energy at PNGB decay, and a curvaton effective equation of state pcurv=−0.9ρcurv.