Abstract
The discovery of non-zero neutrino masses invites one to consider decays of heavier neutrinos into lighter ones. We investigate the impact of two-body decays of neutrinos on the neutronization burst of a core-collapse supernova -- the large burst of $\nu_e$ during the first 25 ms post core-bounce. In the models we consider, the $\nu_e$, produced mainly as a $\nu_3\,(\nu_2)$ in the normal (inverted) mass ordering, are allowed to decay to $\nu_1\,(\nu_3)$ or $\bar{\nu}_1\,(\bar{\nu}_3)$, and an almost massless scalar. These decays can lead to the appearance of a neutronization peak for a normal mass ordering or the disappearance of the same peak for the inverted one, thereby allowing one mass ordering to mimic the other. Simulating supernova-neutrino data at the Deep Underground Neutrino Experiment (DUNE) and the Hyper-Kamiokande (HK) experiment, we compute their sensitivity to the neutrino lifetime. We find that, if the mass ordering is known, and depending on the nature of the Physics responsible for the neutrino decay, DUNE is sensitive to lifetimes $\tau/m \lesssim 10^6$ s/eV for a galactic SN sufficiently close-by (around 10 kpc), while HK is sensitive to lifetimes $\tau/m \lesssim 10^7$ s/eV. These sensitivities are far superior to existing limits from solar-system-bound oscillation experiments. Finally, we demonstrate that using a combination of data from DUNE and HK, one can, in general, distinguish between decaying Dirac neutrinos and decaying Majorana neutrinos.
Highlights
The fact that neutrinos have nonzero masses [1] invites several questions related to other unknown neutrino properties, among those the values of the neutrino lifetimes
If the mass ordering is known and depending on the nature of the physics responsible for the neutrino decay, Deep Underground Neutrino Experiment (DUNE) is sensitive to lifetimes τ=m ≲ 106 s=eV for a Galactic supernova sufficiently close by, while HK is sensitive to lifetimes τ=m ≲ 107 s=eV
Given everything currently known about the neutrinos, one can affirm that the two heavier neutrinos—ν3, ν2 in the case of the so-called normal mass ordering (NMO) and ν2, ν1 in the case of the so-called inverted mass ordering (IMO)—have nonzero mass and finite lifetime [2,3,4,5,6,7,8]
Summary
The fact that neutrinos have nonzero masses [1] invites several questions related to other unknown neutrino properties, among those the values of the neutrino lifetimes. Considering invisible decays, the current bounds imposed from the analysis of the SNO data, combined with other solar neutrino experiments, results in the lifetime of τ2=m2 > 1.92 × 10−3 s=eV at 90% confidence [41]. More stringent bounds [15,36] are expected from next-generation neutrino oscillation experiments including the JUNO [42] and Deep Underground Neutrino Experiment (DUNE) [43] experiments, while stronger but modeldependent bounds—τ3=m3 > 2.2 × 10−5 s=eV—from solar neutrinos have been recently proposed [17] These rather loose bounds lead one to explore baselines which are much longer than 1 A.U. Two candidates immediately qualify for the search:.
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