Gamma-Ray Constraints on the First Stars from Annihilation of Light WIMPs

TL;DR

This paper investigates gamma-ray signals from early universe dark matter minihalos hosting the first stars, focusing on light WIMP dark matter and its annihilation channels, to constrain dark matter properties and early star formation.

Contribution

It provides new limits on the fraction of early dark matter minihalos capable of hosting the first stars based on gamma-ray constraints and dark matter annihilation models.

Findings

Light dark matter implies small black hole sizes or specific annihilation channels with low gamma-ray luminosity.

Certain early minihalos likely did not host the first stars due to dark matter properties.

Constraints suggest limited dark matter annihilation in early minihalos.

Abstract

We calculate the limits on the fraction of viable dark matter minihalos in the early universe to host Population III.1 stars, surviving today as dark matter spikes in our Milky Way halo. Motivated by potential hints of light dark matter from the DAMA and CoGeNT direct dark matter searches, we consider thermal relic WIMP dark matter with masses of 5, 10, and 20 GeV, and annihilation to mu^+ mu^-, tau^+ tau^-, and q bar{q}. From this brief study we conclude that, if dark matter is light, either the typical black hole size is \lesssim 100 M_\odot (i.e. there is no significant Dark Star phase), and/or dark matter annihilates primarily to mu^+ mu^- or other final states that result in low gamma-ray luminosity, and/or that an extremely small fraction of minihalos in the early universe that seem suitable to host the formation of the first stars actually did.