The Effects Of Relativistic Hidden Sector Particles on the Matter Power Spectrum

Understand

If dark matter resides in a hidden sector minimally coupled to the Standard Model, another particle within the hidden sector might dominate the energy density of the early universe temporarily, causing an early matter-dominated era (EMDE).

• During an EMDE, matter perturbations grow more rapidly than they would in a period of radiation domination, which leads to the formation of microhalos much earlier than they would form in standard cosmological scenarios.
• These microhalos boost the dark matter annihilation signal, but this boost is highly sensitive to the small-scale cut-off in the matter power spectrum.
• If the dark matter is sufficiently cold, this cut-off is set by the relativistic pressure of the particle that dominates the hidden sector.