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Register a new userDecoherence in neutrino propagation through matter, and bounds from IceCube/DeepCore
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We revisit neutrino oscillations in matter considering the open quantum system framework which allows to introduce possible decoherence effects generated by New Physics in a phenomenological manner. We assume that the decoherence parameters $gamma_{ij}$ may depend on the neutrino energy, as $gamma_{ij}=gamma_{ij}^{0}(E/text{GeV})^n$ $(n = 0,pm1,pm2) $. The case of non-uniform matter is studied in detail, both within the adiabatic approximation and in the more general non-adiabatic case. In particular, we develop a consistent formalism to study the non-adiabatic case dividing the matter profile into an arbitrary number of layers of constant densities. This formalism is then applied to explore the sensitivity of IceCube and DeepCore to this type of effects. Our study is the first atmospheric neutrino analysis where a consistent treatment of the matter effects in the three-neutrino case is performed in presence of decoherence. We show that matter effects are indeed extremely relevant in this context. We find that IceCube is able to considerably improve over current bounds in the solar sector ($gamma_{21}$) and in the atmospheric sector ($gamma_{31}$ and $gamma_{32}$) for $n=0,1,2$ and, in particular, by several orders of magnitude (between 3 and 9) for the $n=1,2$ cases. For $n=0$ we find $gamma_{32},gamma_{31}< 4.0cdot10^{-24} (1.3cdot10^{-24})$ GeV and $gamma_{21}<1.3cdot10^{-24} (4.1cdot10^{-24})$ GeV, for normal (inverted) mass ordering.
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As atmospheric neutrinos propagate through the Earth, vacuum-like oscillations are modified by Standard-Model neutral- and charged-current interactions with electrons. Theories beyond the Standard Model introduce heavy, TeV-scale bosons that can produce nonstandard neutrino interactions. These additional interactions may modify the Standard Model matter effect producing a measurable deviation from the prediction for atmospheric neutrino oscillations. The result described in this paper constrains nonstandard interaction parameters, building upon a previous analysis of atmospheric muon-neutrino disappearance with three years of IceCube-DeepCore data. The best fit for the muon to tau flavor changing term is $epsilon_{mu tau}=-0.0005$, with a 90% C.L. allowed range of $-0.0067 <epsilon_{mu tau}< 0.0081$. This result is more restrictive than recent limits from other experiments for $epsilon_{mu tau}$. Furthermore, our result is complementary to a recent constraint on $epsilon_{mu tau}$ using another publicly available IceCube high-energy event selection. Together, they constitute the worlds best limits on nonstandard interactions in the $mu-tau$ sector.
We study the effects of non-standard interactions on the oscillation pattern of atmospheric neutrinos. We use neutrino oscillograms as our main tool to infer the role of non-standard interactions (NSI) parameters at the probability level in the energy range, $E in [1,20]$ GeV and zenith angle range, $cos theta in [-1,0]$. We compute the event rates for atmospheric neutrino events in presence of NSI parameters in the energy range $E in [1,10]$ GeV for two different detector configurations - a magnetized iron calorimeter and an unmagnetized liquid Argon time projection chamber which have different sensitivities to NSI parameters due to their complementary characteristics. As an application, we discuss how NSI parameter, $epsilon_{mutau}$ impacts the determination of the correct octant of $theta_{23}$.
Environmental decoherence of oscillating neutrinos of strength $Gamma = (2.3 pm 1.1) times 10^{-23}$ GeV can explain how maximal $theta_{23}$ mixing observed at 295 km by T2K appears to be non-maximal at longer baselines. As shown recently by R. Oliveira, the MSW matter effect for neutrinos is altered by decoherence: In normal (inverted) mass hierarchy, a resonant enhancement of $ u_{mu} (bar{ u}_{mu}) rightarrow u_{e} (bar{ u}_{e})$ occurs for $6 < E_{ u} < 20$ GeV. Thus decoherence at the rated strength may be detectable as an excess of charged-current $ u_{e}$ events in the full $ u_{mu}$ exposures of MINOS+ and OPERA.
While the low-energy excess observed at MiniBooNE remains unchallenged, it has become increasingly difficult to reconcile it with the results from other sterile neutrino searches and cosmology. Recently, it has been shown that non-minimal models with new particles in a hidden sector could provide a better fit to the data. As their main ingredients they require a GeV-scale $Z$, kinetically mixed with the photon, and an unstable heavy neutrino with a mass in the 150 MeV range that mixes with the light neutrinos. In this letter we point out that atmospheric neutrino experiments (and, in particular, IceCube/DeepCore) could probe a significant fraction of the parameter space of such models by looking for an excess of double-bang events at low energies, as proposed in our previous work (arXiv:1707.08573). Such a search would probe exactly the same production and decay mechanisms required to explain the anomaly.
We report constraints on nonstandard neutrino interactions (NSI) from the observation of atmospheric neutrinos with IceCube, limiting all individual coupling strengths from a single dataset. Furthermore, IceCube is the first experiment to constrain flavor-violating and nonuniversal couplings simultaneously. Hypothetical NSI are generically expected to arise due to the exchange of a new heavy mediator particle. Neutrinos propagating in matter scatter off fermions in the forward direction with negligible momentum transfer. Hence the study of the matter effect on neutrinos propagating in the Earth is sensitive to NSI independently of the energy scale of new physics. We present constraints on NSI obtained with an all-flavor event sample of atmospheric neutrinos based on three years of IceCube DeepCore data. The analysis uses neutrinos arriving from all directions, with reconstructed energies between 5.6 GeV and 100 GeV. We report constraints on the individual NSI coupling strengths considered singly, allowing for complex phases in the case of flavor-violating couplings. This demonstrates that IceCube is sensitive to the full NSI flavor structure at a level competitive with limits from the global analysis of all other experiments. In addition, we investigate a generalized matter potential, whose overall scale and flavor structure are also constrained.
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