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Abstract A novel approach is proposed to reveal a secret birth of enhanced circumstellar material (CSM) surrounding a collapsing massive star using neutrinos as a unique probe. In this scheme, nonthermal TeV-scale neutrinos produced in ejecta–CSM interactions are tied with thermal MeV neutrinos emitted from a pre-explosion burning process, based on a scenario that CSM had been formed via the presupernova activity. Taking a representative model of the presupernova neutrinos, the spectrum and light curve of the corresponding high-energy CSM neutrinos are calculated at multiple mass-loss efficiencies, which are considered as a systematic uncertainty. In addition, as a part of the method demonstration, the detected event rates along time at JUNO and IceCube, as representative detectors, are estimated for the presupernova and CSM neutrinos, respectively, and are compared with the expected background rate at each detector. The presented method is found to be reasonably applicable for the range up to ∼1 kpc and even farther with future experimental efforts. The potentialities of other neutrino detectors, such as SK-Gd, Hyper-Kamiokande, and KM3NeT, are also discussed. This is a pioneering work of performing astrophysics with neutrinos from diverse energy regimes, initiating multienergy neutrino astronomy in the forthcoming era where next-generation large-scale neutrino telescopes are operating. 

Abstract The flux spectrum, event rate, and experimental sensitivity are investigated for the diffuse supernova (SN) neutrino background (DSNB), which originates from past stellar collapses and is also known as a supernova relic neutrino background. For this purpose, the contribution of collapses that lead to successful supernova explosion and black hole (BH) formation simultaneously, which are suggested to be a nonnegligible population from the perspective of Galactic chemical evolution, is taken into account. If the BH-forming SNe involve matter fallback onto the protoneutron star for the long term, their total emitted neutrino energy becomes much larger than that of ordinary SNe and failed SNe (BH formation without explosion). Then, in the case of the normal mass hierarchy in neutrino oscillations and with half of all core-collapse SNe being BH-forming SNe, the expected event rate according to the current DSNB model is enhanced by up to a factor of 2 due to the BH-forming SNe. While substantial uncertainties exist regarding the duration of the matter fallback, which determines the total amount of emitted neutrinos, and the fraction of BH-forming SNe, the operation time required to detect the DSNB at Hyper-Kamiokande would be reduced by such contribution in any case. 

Abstract The flux of neutrinos from annihilation of gravitationally captured dark matter in the Sun has significant constraints from direct-detection experiments. However, these constraints are relaxed for inelastic dark matter as inelastic dark matter interactions generate less energetic nuclear recoils compared to elastic dark matter interactions. In this paper, we explore the possibility for large volume underground neutrino experiments to detect the neutrino flux from captured inelastic dark matter in the Sun. The neutrino spectrum has two components: a mono-energetic “spike” from pion and kaon decays at rest and a broad-spectrum “shoulder” from prompt primary meson decays. We focus on detecting the shoulder neutrinos from annihilation of hadrophilic inelastic dark matter with masses in the range 4–100 GeV and the mass splittings in up to 300 keV. We determine the event selection criterion for DUNE to identify GeV-scale muon neutrinos and anti-neutrinos originating from hadrophilic dark matter annihilation in the Sun, and forecast the sensitivity from contained events. We also map the current bounds from Super-Kamiokande and IceCube on elastic dark matter, as well as the projected limits from Hyper-Kamiokande, to the parameter space of inelastic dark matter. We find that there is a region of parameter space that these neutrino experiments are more sensitive to than the direct-detection experiments. For dark matter annihilation to heavy-quarks, the projected sensitivity of DUNE is weaker than current (future) Super (Hyper) Kamiokande experiments. However, for the light-quark channel, only the spike is observable and DUNE will be the most sensitive experiment.