Cannibal domination and the matter power spectrum

Decoupled hidden sectors can easily and generically result in a period of cannibal domination, during which the dominant component Universe has an equation state intermediate between radiation matter due to self-heating by number-changing interactions. We present for first time consequences cannibal-dominated era prior big bang nucleosynthesis structure formation on small scales. find that early imprints characteristic peak dark power spectrum, with scale amplitude directly determined mass, lifetime, interaction strength field. This enhancement small-scale spectrum will generate early-forming microhalos, we provide detailed transparent map properties species mass these structures. These relations demonstrate how internal workings sector leave potentially observable imprint even if no direct couplings Standard Model.