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If the heaviest neutrino mass eigenstate is unstable, its decay modes could include lighter neutrino eigenstates. In this case part of the decay products could be visible, as they would interact at neutrino detectors via mixing. At neutrino oscillation experiments, a characteristic signature of such \emph{visible neutrino decay} would be an apparent excess of events at low energies. We focus on a simple phenomenological model in which the heaviest neutrino decays as $\nu_3 \rightarrow \nu_{1,2} + \phi$, where $\phi$ is a new light scalar. If neutrinos are Majorana particles the helicity-flipping decays would be observable (i.e., $\nu \to \bar\nu + \phi$), leading to interesting observable consequences on the event rates. We compute the sensitivities of the Deep Underground Neutrino Experiment (DUNE) to the couplings of the new scalar as a function of the lightest neutrino mass. Under the assumption that only the heaviest neutrino is unstable, and for a normal mass ordering, we find that DUNE will be sensitive to values of $\tau_3/m_3 > 1.95 - 2.6\times 10^{-10}$~s/eV (90\% C.L.) (depending on the lightest neutrino mass), where $\tau_3$ and $m_3$ are the lifetime and mass of $\nu_3$, respectively., Comment: 17 pages, 7 figures

We investigate the present constraints from MINOS and T2K experiments for the neutrino decay scenario induced by non-diagonal couplings of Majorons to neutrinos. As novelty, on top of the typical invisible decay prescription, we add the contribution of visible decay, where final products can be observed. This new effect depends on the nature of the neutrino - Majoron coupling, which can be of scalar or pseudoscalar type. Using the combination of disappearance data from MINOS and disappearance and appearance data from T2K, for normal ordering, we constrain the decay parameter $\alpha\equiv E\,\Gamma$ for the heaviest neutrino, where $E$ and $\Gamma$ are the neutrino energy and width, respectively. We find that when considering visible decay within appearance data, one can improve current neutrino long-baseline constraints up to $\alpha< \mathcal{O}(10^{-5})$ eV$^2$, at 90\% C.L., for both kinds of couplings, which is better by one order of magnitude compared to previous bounds., Comment: 29 pages, 8 figures, 3 appendices; v2: Corrected errors, version accepted for publication in JHEP

Long gamma-ray bursts (GRBs) are associated with the gravitational collapse of very massive stars. The central engine of a GRB can collimate relativistic jets that propagate inside the stellar envelope. The shock waves produced when the jet disrupts the stellar surface are capable of accelerating particles up to very high energies. If the jet has hadronic content, neutrinos will be produced via charged pion decays. The main goal of this work is to estimate the neutrino emission produced in the region close to the surface of the star, taking pion and muon cooling into account, along with subtle effects arising from neutrino production in a highly magnetized medium. We estimate the maximum energies of the different kinds of particles and solve the coupled transport equations for each species. Once the particle distributions are known, we calculate the intensity of neutrinos. We study the different effects on the neutrinos that can change the relative weight of different flavors. In particular, we consider the effects of neutrino oscillations, and of neutrino spin precession caused by strong magnetic fields. The expected neutrino signals from the shocks in the uncorking regions of Population III events is very weak, but the neutrino signal produced by Wolf-Rayet GRBs with $z<0.5$ is not far from the level of the atmospheric background. The IceCube experiment does not have the sensitivity to detect neutrinos from the implosion of the earliest stars, but a number of high-energy neutrinos may be detected from nearby long GRBs. The cumulative signal should be detectable over several years ($\sim 10$ yr) of integration with the full 86-string configuration., Comment: 11 pages, 7 figures, accepted for publication in A&A

The forthcoming experiments on neutrino mass measurement using beta decay, open a new window to explore the Large Extra Dimension model. The Kaluza-Klein tower of neutrinos in Large Extra Dimension contribute to the Kurie function of beta decay that can be tested kinematically. In addition to providing an alternative approach using just the kinematical properties, we show that KATRIN can probe the compactification radius of extra dimensions down to 0.2 \mu m which is better, at least by a factor of two, than the upper limits from neutrino oscillation experiments., Comment: 4 pages, 4 figures; v2: discussion improved, matches the version published at PLB

Two of the most fundamental properties of the dark matter particle, the mass and the lifetime, are only weakly constrained by the astronomical and cosmological evidence of dark matter. We derive in this paper lower limits on the lifetime of dark matter particles with masses in the range 10 TeV-10^15 TeV from the non-observation of ultrahigh energy neutrinos in the AMANDA, IceCube, Auger and ANITA experiments. For dark matter particles which produce neutrinos in a two body or a three body decay, we find that the dark matter lifetime must be longer than O(10^26-10^28) s for masses between 10 TeV and the Grand Unification scale. Finally, we also calculate, for concrete particle physics scenarios, the limits on the strength of the interactions that induce the dark matter decay., Comment: 17 pages, 6 figures; v2: references added, discussion improved, matches the version published at JCAP

The presence of light sterile neutrinos would strongly modify the energy spectrum of the Tritium \beta-electrons. We perform an analysis of the KATRIN experiment's sensitivity by scanning almost all the allowed region of neutrino mass-squared difference and mixing angles of the 3+1 scenario. We consider the effect of the unknown absolute mass scale of active neutrinos on the sensitivity of KATRIN to the sterile neutrino mass. We show that after 3 years of data-taking, the KATRIN experiment can be sensitive to mixing angles as small as sin^2 (2\theta_s) ~ 10^-2. Particularly we show that for small mixing angles, sin^2 (2\theta_s) < 0.1, the KATRIN experiment can gives the strongest limit on active-sterile mass-squared difference., Comment: 4 pages, 2 figures, matches the published version

The recent global fit of short baseline neutrino oscillation data favors the presence of one (or more) sterile neutrino state which leads to new mass splitting \Delta m^2 ~1 eV^2. We consider the effect of this new states on the evolution of neutrinos from the dark matter annihilation inside the Sun. We show that neutrinos with energy E_\nu > 100 GeV undergo resonant active-sterile oscillation which depletes the flux of neutrinos arriving at the Earth. As an example of this effect, we present the oscillation probabilities for the case of monochromatic neutrinos from the direct annihilation of dark matter particles to neutrinos and the depletion due to the presence of sterile neutrinos., Comment: 13 pages, 8 figures, matches the published version

We analyze the 1496 days of SuperKamiokande data to put limits on the nue, anti-nue, numu + nutau and anti-numu + anti-nutau components of the diffuse flux of supernova neutrinos, in different energy intervals and for different neutrino energy spectra. By considering the presence of only one component at a time, we find the following bounds at 90% C.L. and for neutrino energy E>19.3$ MeV: Phi_{nue}<73.3-154 cm^-2 s^-1, Phi_{anti-nue} <1.4-1.9 cm^-2 s^-1, Phi_{numu+nutau} <(1.0-1.4) 10^3 cm^-2 s^-1, and Phi_{anti-numu+ anti-nutau} <(1.3-1.8) 10^3 cm^-2 s^-1, where the intervals account for varying the neutrino spectrum. In the interval E = 22.9 - 36.9 MeV, we find Phi_{nue}<39-54 cm^-2 s^-1, which improves on the existing limit from SNO in the same energy window. Our results for numu + nutau and anti-numu + anti-nutau improve by about four orders of magnitude over the previous best constraints from LSD., Comment: PDFLaTeX, 27 pages, eight figures, six tables; revised version with two new figures; accepted in JCAP