Cannibal domination and the matter power spectrum

Abstract

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

5 pages + appendices, 4 figures; matches version accepted in PRD

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• Dark Matter Microhalos From Simplified Models
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• Gravothermalizing into primordial black holes, boson stars, and cannibal stars
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• Freezing-in Cannibal Dark Sectors
• The cusp-halo relation
• Limits on Early Matter Domination from the Isotropic Gamma-Ray Background
• Cosmology of Single Species Hidden Dark Matter
• Bispectrum of induced gravitational waves in the poltergeist mechanism