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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.
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We investigate the implications of one light eV scale sterile neutrino on the physics potential of the proposed long-baseline experiment DUNE. If the future short-baseline experiments confirm the existence of sterile neutrinos, then it can affect the mass hierarchy (MH) and CP-violation (CPV) searches at DUNE. The MH sensitivity still remains above 5$sigma$ if the three new mixing angles ($theta_{14}, theta_{24}, theta_{34}$) are all close to $theta_{13}$. In contrast, it can decrease to 4$sigma$ if the least constrained mixing angle $theta_{34}$ is close to its upper limit $sim 30^0$. We also assess the sensitivity to the CPV induced both by the standard CP-phase $delta_{13} equiv delta$, and the new CP-phases $delta_{14}$ and $delta_{34}$. In the 3+1 scheme, the discovery potential of CPV induced by $delta_{13}$ gets deteriorated compared to the 3$ u$ case. In particular, the maximal sensitivity (reached around $delta_{13}$ $sim$ $pm$ $90^0$) decreases from $5sigma$ to $4sigma$ if all the three new mixing angles are close to $theta_{13}$. It can further diminish to almost $3sigma$ if $theta_{34}$ is large ($sim 30^0$). The sensitivity to the CPV due to $delta_{14}$ can reach 3$sigma$ for an appreciable fraction of its true values. Interestingly, $theta_{34}$ and its associated phase $delta_{34}$ can influence both the $ u_e$ appearance and $ u_mu$ disappearance channels via matter effects, which in DUNE are pronounced. Hence, DUNE can also probe CPV induced by $delta_{34}$ provided $theta_{34}$ is large. We also reconstruct the two phases $delta_{13}$ and $delta_{14}$. The typical 1$sigma$ uncertainty on $delta_{13}$ ($delta_{14}$) is $sim20^0$ ($30^0$) if $theta_{34} =0$. The reconstruction of $delta_{14}$ (but not that of $delta_{13}$) degrades if $theta_{34}$ is large.
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 explore the capabilities of the upcoming Deep Underground Neutrino Experiment (DUNE) to measure $ u_tau$ charged-current interactions and the associated oscillation probability $P( u_mu to u_tau)$ at its far detector, concentrating on how such results can be used to probe neutrino properties and interactions. DUNE has the potential to identify significantly more $ u_tau$ events than all existing experiments and can use this data sample to nontrivially test the three-massive-neutrinos paradigm by providing complementary measurements to those from the $ u_e$ appearance and $ u_mu$ disappearance channels. We further discuss the sensitivity of the $ u_tau$ appearance channel to several hypotheses for the physics that may lurk beyond the three-massive-neutrinos paradigm: a non-unitary lepton mixing matrix, the $3+1$ light neutrinos hypothesis, and the existence of non-standard neutral-current neutrino interactions. Throughout, we also consider the relative benefits of the proposed high-energy tune of the Long-Baseline Neutrino Facility (LBNF) beam-line.
We study the physics reach of the long-baseline oscillation analysis of the DUNE experiment when realistic simulations are used to estimate its neutrino energy reconstruction capabilities. Our studies indicate that significant improvements in energy resolution compared to what is customarily assumed are plausible. This improved energy resolution can increase the sensitivity to leptonic CP violation in two ways. On the one hand, the CP-violating term in the oscillation probability has a characteristic energy dependence that can be better reproduced. On the other hand, the second oscillation maximum, especially sensitive to $delta_{CP}$, is better reconstructed. These effects lead to a significant improvement in the fraction of values of $delta_{CP}$ for which a $5 sigma$ discovery of leptonic CP-violation would be possible. The precision of the $delta_{CP}$ measurement could also be greatly enhanced, with a reduction of the maximum uncertainties from $26^circ$ to $18^circ$ for a 300~MW$cdot$kt$cdot$yr exposure. We therefore believe that this potential gain in physics reach merits further investigations of the detector performance achievable in DUNE.
In this work we analyze quantum decoherence in neutrino oscillations considering the Open Quantum System framework and oscillations through matter for three neutrino families. Taking DUNE as a case study we performed sensitivity analyses for two neutrino flux configurations finding limits for the decoherence parameters. We also offer a physical interpretation for a new peak which arises at the $ u_{e}$ appearance probability with decoherence. The best sensitivity regions found for the decoherence parameters are $Gamma_{21}le 1.2times10^{-23},text{GeV}$ and $Gamma_{32}le 7.7times10^{-25},text{GeV}$ at $90%$ C. L.
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