Constraints on small-scale cosmological perturbations from gamma-ray searches for dark matter

TL;DR

This paper investigates how gamma-ray observations of ultracompact minihalos (UCMHs) can constrain small-scale primordial density perturbations, offering a new method beyond primordial black hole limits.

Contribution

It introduces gamma-ray flux analysis from UCMHs as a novel probe for small-scale cosmological perturbations, expanding the tools for early Universe model discrimination.

Findings

Gamma-ray fluxes from UCMHs can be used to set limits on primordial power spectrum.

Non-observation of UCMHs by Fermi constrains small-scale perturbations.

UCMHs provide a promising indirect detection method for dark matter and early Universe physics.

Abstract

Events like inflation or phase transitions can produce large density perturbations on very small scales in the early Universe. Probes of small scales are therefore useful for e.g. discriminating between inflationary models. Until recently, the only such constraint came from non-observation of primordial black holes (PBHs), associated with the largest perturbations. Moderate-amplitude perturbations can collapse shortly after matter-radiation equality to form ultracompact minihalos (UCMHs) of dark matter, in far greater abundance than PBHs. If dark matter self-annihilates, UCMHs become excellent targets for indirect detection. Here we discuss the gamma-ray fluxes expected from UCMHs, the prospects of observing them with gamma-ray telescopes, and limits upon the primordial power spectrum derived from their non-observation by the Fermi Large Area Space Telescope.