Low-Energy Neutrinos from Primordial Black Holes: A New Possibility for Observing Hawking Radiation

Abstract: The study of primordial black holes (PBHs) and the Hawking radiation they produce represents a significant step toward understanding the role of these phenomena in the cosmological evolution of the Universe. PBHs could be a component of dark matter, the seeds of supermassive black holes, and sources of Hawking radiation, which, unlike the radiation from other black holes, might be observable. Over the course of the evolution of the Universe from the Big Bang to the present day, PBHs have lost a substantial portion of their mass through neutrino radiation. This occurs because, for black holes with masses $M\lesssim10^{23}\,$g, the radiation of the lightest massive particles - neutrinos - becomes significant alongside the emission of photons. This neutrino radiation eventually dominates the emission process. By the present time ($t_0=13.8$ Gyr), only black holes with masses $\lesssim 10^{15}\,$g have largely evaporated, meaning that the total emission spectrum of PBHs is now dominated by the neutrino component. In this paper, we present new estimates of the neutrino spectra emitted by PBHs of various masses, with a particular focus on low-energy radiation ($E_{kin} \in [0.01 \div 1]\, $eV) for the first time. Our calculations demonstrate that black holes in the mass range $[10^{9}\div10^{11}]\,$g emit neutrinos with intensities that exceed the background fluxes from known astrophysical sources in the low-energy range. In contrast, in the high-energy range, the emission remains below the background level, consistent with observational constraints. These findings open new avenues for the potential detection of PBH radiation and could stimulate advancements in neutrino detection technologies, particularly in the low-energy regime. The observation of neutrinos in this energy range represents one of the few opportunities to confirm the existence of Hawking radiation.