Vid Iršič: Early Structure Formation Constraints on the Ultra-Light Axion in the Post-Inflation Scenario

Early Structure Formation Constraints on the Ultra-Light Axion in the Post-Inflation Scenario

Vid Iršič

University of Washington, Seatle, WA, USA

Many works have concentrated on the observable signatures of the dark matter being an ultralight axion-like particle (ALP). We concentrate on a particularly dramatic signature in the power spectrum of density inhomogeneities that occurs if the symmetry breaking that establishes the ALP happens after inflation – white fluctuations that dominate the RMS density fluctuations at small-scales. We find that for symmetry breaking scales of f_A ∼ 10^13 − 10^15 GeV, which requires a high effective maximum temperature after inflation, ALP dark matter can significantly alter the early history of structure formation, the reionization history, and the Lyα forest. In this talk I present some preliminary results coming from the current observables, excluding f_A > 1×10^15 GeV (and particle masses of m_A < 0.5×10^−17 eV) in the simplest model and considerably lower in models coupled to a hidden strongly interacting sector (f_A > 1 × 10^13 GeV and m_A < 0.5 × 10^−12 eV). Future 21 cm observations have the potential to improve these constraints further using the z ∼ 20 − 30 shock heating from the supersonic motions of ∼ 10^4 M_Sun ALP structures.