Democratic Primordial Matter

UV completions of the Standard Model often imply a plentitude of hidden sectors, very weakly coupled to our visible sector. As it is natural to assume that the inflaton should reheat all sectors democratically, it is surprising that the Standard Model dominates the entropy density at late time. Given this assumption of democratic inflaton decay, we investigate the requirements to recover standard cosmology, and present a broad class of models in which this is automatically accomplished. We outline a framework in which long-lived heavy states result in entropy injection to the visible sector, but not the hidden sectors, and thus lead to late time entropy dominance of the Standard Model. This scenario has a number of interesting consequences, in particular the dark matter, which is a primordial relic, can be substantially colder than a traditional thermal relic, and consequently can be lighter without conflicting with cosmological bounds. Moreover, we give an elegant implementation in which decays of the heavy right-handed neutrino leads to late time reheating of the Standard Model degrees of freedom, and also provides suitable conditions for non-thermal leptogenesis.