Gamma rays from ultracompact primordial dark matter minihalos

Abstract: Ultracompact minihalos have recently been proposed as a new class of dark matter structure. These minihalos would be produced by phase transitions in the early Universe or features in the inflaton potential, and constitute non-baryonic massive compact halo objects (MACHOs) today. We examine the prospect of detecting ultracompact minihalos in gamma-rays if dark matter consists of self-annihilating particles. We compute present-day fluxes from minihalos produced in the electron-positron annihilation epoch, and the QCD and electroweak phase transitions in the early Universe. Even at a distance of 100 pc, minihalos produced during the electron-positron annihilation epoch should be eminently detectable today, either by the Fermi satellite, current Air Cherenkov telescopes, or even in archival EGRET data. Within ~1 pc, minihalos formed in the QCD phase transition would have similar predicted fluxes to the dwarf spheroidal galaxies targeted by current indirect dark matter searches, so might also be detectable by present or upcoming experiments.