2025/03/04 by Lambiase, Gaetano, Poddar, Tanmay Kumar, Visinelli, Luca · 3 citations
#Cosmology and Nongalactic Astrophysics (astro-ph.CO) #FOS: Physical sciences #General Relativity and Quantum Cosmology (gr-qc) #High Energy Physics - Phenomenology (hep-ph) #High Energy Physics - Theory (hep-th)
paper · doi:10.48550/arxiv.2503.02940
We assess the effect of the Cosmic Neutrino Background (CνB) on superradiant instabilities caused by an ultralight scalar field around spinning black holes (BHs). When the scalar couples to neutrinos via a Yukawa interaction, thermal corrections from the CνB induce a quartic self-interaction and an effective mass term for the scalar. We show that, for Yukawa couplings as small as yϕν ∼ 10-16 (for astrophysical BHs) or 10-20 (for supermassive BHs), the quartic term can quench the instability and set observable bounds, even if the scalar does not constitute dark matter. We assess the robustness of these constraints against several sources of uncertainty, including gravitational focusing of relic neutrinos, galactic clustering, and non-linear backreaction. An enhanced local neutrino density weakens the bounds by up to an order of magnitude compared to a uniform background, yet the induced self-interaction remains strong enough to significantly affect the superradiant dynamics. Our results open a new observational window on neutrino-coupled scalars via BH superradiance.