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Register a new userNeutrino Invisible Decay at DUNE: a multi-channel analysis
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The hypothesis of the decay of neutrino mass eigenstates leads to a substantial modification of the appearance and disappearance probabilities of flavor eigenstates. We investigate the impact on the standard oscillation scenario caused by the decay of the heaviest mass eigenstate $ u_3$ (with a mass $m_3$ and a mean life $tau_3$) to a sterile state in DUNE. We find that the lower bound of $5.1 times 10^{-11}~s/eV$ at 90% CL on the decay parameter $tau_3/m_3$ can be set if the Neutral Current data are included in the analysis, thus providing the best long-baseline expected limit so far. We also show that the $ u_tau$ appearance channel would give only a negligible contribution to the decay parameter constraints. Our numerical results are corroborated by analytical formulae for the appearance and disappearance probabilities in vacuum (which is a useful approximation for the study of the invisible decay model) that we have developed up to the second order in the solar mass splitting and to all orders in the decay factor $t/tau_3$.
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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 $ u_3 rightarrow u_{1,2} + phi$, where $phi$ is a new light scalar. If neutrinos are Majorana particles the helicity-flipping decays would be observable (i.e., $ u to bar u + 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 $tau_3/m_3 > 1.95 - 2.6times 10^{-10}$~s/eV (90% C.L.) (depending on the lightest neutrino mass), where $tau_3$ and $m_3$ are the lifetime and mass of $ u_3$, respectively.
We investigate the potential for the Deep Underground Neutrino Experiment (DUNE) to probe the existence and effects of a fourth neutrino mass-eigenstate. We study the mixing of the fourth mass-eigenstate with the three active neutrinos of the Standard Model, including the effects of new sources of CP-invariance violation, for a wide range of new mass-squared differences, from lower than 10^-5 eV^2 to higher than 1 eV^2. DUNE is sensitive to previously unexplored regions of the mixing angle - mass-squared difference parameter space. If there is a fourth neutrino, in some regions of the parameter space, DUNE is able to measure the new oscillation parameters (some very precisely) and clearly identify two independent sources of CP-invariance violation. Finally, we use the hypothesis that there are four neutrino mass-eigenstates in order to ascertain how well DUNE can test the limits of the three-massive-neutrinos paradigm. In this way, we briefly explore whether light sterile neutrinos can serve as proxies for other, in principle unknown, phenomena that might manifest themselves in long-baseline neutrino oscillation experiments.
Several theories of particle physics beyond the Standard Model consider that neutrinos can decay. In this work we assume that the standard mechanism of neutrino oscillations is altered by the decay of the heaviest neutrino mass state into a sterile neutrino and, depending on the model, a scalar or a Majoron. We study the sensitivity of the forthcoming KM3NeT-ORCA experiment to this scenario and find that it could improve the current bounds coming from oscillation experiments, where three-neutrino oscillations have been considered, by roughly two orders of magnitude. We also study how the presence of this neutrino decay can affect the determination of the atmospheric oscillation parameters $sin^2theta_{23}$ and $Delta m_{31}^2$, as well as the sensitivity to the neutrino mass ordering.
We study the physics potential of the long-baseline experiments T2HK, T2HKK and ESS$ u$SB in the context of invisible neutrino decay. We consider normal mass ordering and assume that the state $ u_{3}$ as unstable, decaying into sterile states during the flight and obtain constraints on the neutrino decay lifetime ($tau_3$). We find that T2HK, T2HKK and ESS$ u$SB are sensitive to the decay-rate of $ u_{3}$ for $tau_{3}/m_{3} leq 2.72times10^{-11}$s/eV, $tau_{3}/m_{3} leq 4.36times10^{-11}$s/eV and $tau_{3}/m_{3} leq 2.43times10^{-11}$s/eV respectively at 3$sigma$ C.L. We compare and contrast the sensitivities of the three experiments and specially investigate the role played by the mixing angle $theta_{23}$. It is seen that for experiments with flux peak near the second oscillation maxima, the poorer sensitivity to $theta_{23}$ results in weaker constraints on the decay lifetime. Although, T2HKK has one detector close to the second oscillation maxima, having another detector at the first oscillation maxima results in superior sensitivity to decay. In addition, we find a synergy between the two baselines of the T2HKK experiment which helps in giving a better sensitivity for $theta_{23}$ in the higher octant. We discuss the octant sensitivity in presence of decay and show that there is an enhancement in sensitivity which occurs due to the contribution from the survival probability $P_{mumu}$ which is more pronounced for the experiments at the second oscillation maxima. We also obtain the combined sensitivity of T2HK+ESS$ u$SB and T2HKK+ESS$ u$SB as $tau_{3}/m_{3} leq 4.36times10^{-11}$s/eV and $tau_{3}/m_{3} leq 5.53times10^{-11}$s/eV respectively at 3$sigma$ C.L.
We study the possibility of probing different texture zero neutrino mass matrices at long baseline neutrino experiment DUNE. Assuming a diagonal charged lepton basis and Majorana nature of light neutrinos, we first classify the possible light neutrino mass matrices with one and two texture zeros and then numerically evaluate the parameter space in terms of atmospheric mixing angle $theta_{23}$ and Dirac CP phase $delta_{text{CP}}$ which satisfies the texture zero conditions. We then feed these parameter values into the numerical analysis in order to study the sensitivity of DUNE experiment to them. We find that the DUNE will be able to exclude some of these texture zero mass matrices which restrict the $(theta_{23}-delta_{text{CP}})$ to a very specific range of values.
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