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GR: Fachverband Gravitation, Relativistische Astrophysik und Kosmologie

GR 8: Gravitational Waves II

GR 8.3: Vortrag

Mittwoch, 18. März 2026, 14:15–14:30, KH 01.016

Gravitational wave backgrounds from trapped axion-like particles — •Daniel Schmitt — Goethe University Frankfurt

Axion-like particles (ALPs) are among the most promising dark matter candidates. While laboratory experiments and astrophysical observations have excluded parts of the viable ALP parameter space, the regime of large ALP decay constants, where the ALP becomes invisible, remains hard to access experimentally. I will discuss the conditions under which such invisible ALPs can generate a sizable primordial gravitational wave (GW) background. In particular, I will focus on ALP production via trapped misalignment, where the oscillations of the pseudoscalar are delayed compared to the conventional misalignment scenario. This can trigger resonances in the equation of motion of both the ALP and a gauge field coupled to the ALP, leading to the exponential growth of horizon-sized fluctuations in the early Universe. Such large anisotropies source stochastic GWs, enabling to probe a large part of the ALP parameter space through future GW observatories.

Keywords: Particle cosmology; Gravitational wave background; Axion-like particles; Dark matter; Tachyonic resonance