Imprints of the Early Universe on Axion Dark Matter Substructure

Understand

Despite considerable experimental progress large parts of the axion-like particle (ALP) parameter space remain difficult to probe in terrestrial experiments.

• In some cases, however, small-scale structure of the ALP dark matter (DM) distribution is strongly enhanced, offering opportunities for astrophysical tests.
• Such an enhancement can be produced by a period of pre-nucleosynthesis early matter domination (EMD).
• This cosmology arises in many ultraviolet completions and generates the correct relic abundance for weak coupling $f_a\sim 10^{16}$ GeV, ALP masses in the range $10^{-13}$ eV $<m_a < 1$ eV, and without fine-tuning of the initial misalignment angle.