Speaker:	Mohammad Aghaie (U. Of Osaka)
Title:	Self-Interaction Bounds on Ultralight Dark Matter Couplings to Matter
Date (JST):	Wed, Nov 04, 2026, 13:30 - 15:00
Place:	Seminar Room A
Abstract:	Ultralight dark matter (ULDM) provides a compelling framework in which particle physics, astrophysics, and cosmology meet. In this talk, I will first briefly review the motivation for ULDM and some of its characteristic phenomenology, before focusing on a bounds on ULDM self-interactions from cosmological and astrophysical observations. I will argue that these bounds are remarkably stringent and, importantly, robust across different physical considerations. I will then explore a simple consequence that has received comparatively little attention. Couplings of ULDM to Standard Model particles generically radiatively induce self-interactions of the dark matter field. Consequently, observational limits on ULDM self-interactions can be translated into indirect constraints on its interactions with ordinary matter. As a proof of principle, I will show how this connection leads to strong constraints on linear ULDM couplings to neutrinos, probing parameter space relevant for neutrino-oscillation searches, as well as on quadratic couplings to electrons and light quarks, where the resulting constraints can compete with or exceed those from equivalence-principle tests. I will also discuss the assumptions behind this argument, possible objections, including questions of radiative stability and naturalness, and the extent to which the resulting bounds can be evaded. The aim of this talk is to highlight a potentially broader lesson: the extraordinary sensitivity of cosmology and astrophysics to ULDM self-interactions may provide a powerful and largely unexplored window onto its couplings to the Standard Model. I will conclude by discussing how far this idea can be extended and what other ULDM interactions might be meaningfully constrained along this direction.

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