Erlangen 2026 – scientific programme
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GR: Fachverband Gravitation, Relativistische Astrophysik und Kosmologie
GR 10: Poster
GR 10.4: Poster
Wednesday, March 18, 2026, 16:15–18:45, Redoutensaal
Constraining the Mass of Ultralight Axions Using the 21-cm Signal During Cosmic Dawn — •Julian Antonio Kleff — Institute for Astrophysics and Geophysics, University of Göttingen, Germany
The aim of my master’s thesis is to constrain the mass of a dark matter candidate called ultralight axions (ULAs). Compared to standard cold dark matter ULAs suppress the halo mass function below the scale of the Jeans mass MJ(mα) which depends on the mass mα of ULAs. Star formation within molecular cooling halos is expected to significantly contribute to the 21-cm signal during cosmic dawn. Efficient molecular cooling, and thus star formation, becomes possible if the critical halo mass Mmol(vcb) is reached, which (among other quantities) is affected by the dark-matter-baryon relative velocity vcb introduced after recombination. This dependence on vcb leads to so called velocity acoustic oscillations (VAOs) in the 21-cm power spectrum on scales k∼ 0.1 Mpc−1. However, once MJ(mα)≫ Mmol(vcb) the dependence of the 21-cm signal on vcb is effectively removed, and thus the VAOs too. As MJ(mα) increases with decreasing mα, smoothly decreasing mα leads to a smooth decline of the amplitude of the VAOs in the 21-cm power spectrum until they vanish completely. The goal of my master’s thesis is to implement the physics of ULAs into the software Zeus21, an analytical tool for the computation of the 21-cm power spectrum, and to utilize the strong dependence of the VAOs on the axion mass to improve current constrains on the axion mass.
Keywords: Ultralight Axions; 21-cm Signal; Cosmic Dawn; Zeus21