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Register a new userCombining Sterile Neutrino Fits to Short Baseline Data with IceCube Data
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Carlos Arg\\\"uelles Delgado
Publication date
2019
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English
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Recent global fits to short-baseline neutrino oscillation data have been performed finding preference for a sterile neutrino solution (3+1) over null. In the most recent iteration, it was pointed out that an unstable sterile neutrino (3+1+decay) may be a better description of the data. This is due to the fact that this model significantly reduces the tension between appearance and disappearance datasets. In this work, we add a one-year IceCube dataset to the global fit obtaining new results for the standard 3+1 and 3+1+decay sterile neutrino scenarios. We find that the 3+1+decay model provides a better fit than the 3+1, even in the presence of IceCube, with reduced appearance to disappearance tension. The 3+1+decay model is a 5.4$sigma$ improvement over the null hypothesis and a 2.8$sigma$ improvement over the standard 3+1 model.
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We examine a framework with light new physics, which couples to the Standard Model only via neutrino mixing. Taking the hints from the short-baseline anomalies seriously and combining them with modern cosmological data and recent IceCube measurements, we obtain surprisingly effective constraints on the hidden force: keV $lesssim M lesssim0.3$ GeV for the mediator mass and $g_{h}>10^{-6}-10^{-3}$ for the coupling constant. Flavor equilibration between the hidden and active neutrinos can be delayed until temperatures of $sim 1$ MeV, but not below $sim 100$ keV. This scenario can be tested with next-generation Cosmic Microwave Background, IceCube, and oscillation experiments.
We present a search for a light sterile neutrino using three years of atmospheric neutrino data from the DeepCore detector in the energy range of approximately $10-60~$GeV. DeepCore is the low-energy sub-array of the IceCube Neutrino Observatory. The standard three-neutrino paradigm can be probed by adding an additional light ($Delta m_{41}^2 sim 1 mathrm{ eV^2}$) sterile neutrino. Sterile neutrinos do not interact through the standard weak interaction, and therefore cannot be directly detected. However, their mixing with the three active neutrino states leaves an imprint on the standard atmospheric neutrino oscillations for energies below 100 GeV. A search for such mixing via muon neutrino disappearance is presented here. The data are found to be consistent with the standard three neutrino hypothesis. Therefore we derive limits on the mixing matrix elements at the level of $|U_{mu4}|^2 < 0.11 $ and $|U_{tau4}|^2 < 0.15 $ (90% C.L.) for the sterile neutrino mass splitting $Delta m_{41}^2 = 1.0$ eV$^2$.
We test the hypothesis of non-radiative neutrinos decay using the latest IceCube data. Namely, we calculate the track-to-shower ratio expected in IceCube for the normal and inverted neutrino mass hierarchy taking into account the uncertainties in neutrino oscillation parameters. We show that the subset of data with energy above 60 TeV actually excludes the possibility of a neutrinos decay at the 1 sigma level of significance for both neutrino mass hierarchies.
Neutrino oscillations in matter provide a unique probe of new physics. Leveraging the advent of neutrino appearance data from NOvA and T2K in recent years, we investigate the presence of CP-violating neutrino non-standard interactions in the oscillation data. We first show how to very simply approximate the expected NSI parameters to resolve differences between two long-baseline appearance experiments analytically. Then, by combining recent NOvA and T2K data, we find a tantalizing hint of CP-violating NSI preferring a new complex phase that is close to maximal: $phi_{emu}$ or $phi_{etau}approx3pi/2$ with $|epsilon_{emu}|$ or $|epsilon_{etau}|sim0.2$. We then compare the results from long-baseline data to constraints from IceCube and COHERENT.
Sterile neutrinos with a mass in the eV range have been invoked as a possible explanation of a variety of short baseline (SBL) neutrino oscillation anomalies. However, if one considers neutrino oscillations between active and sterile neutrinos, such neutrinos would have been fully thermalised in the early universe, and would be therefore in strong conflict with cosmological bounds. In this study we first update cosmological bounds on the mass and energy density of eV-scale sterile neutrinos. We then perform an updated study of a previously proposed model in which the sterile neutrino couples to a new light pseudoscalar degree of freedom. Consistently with previous analyses, we find that the model provides a good fit to all cosmological data and allows the high value of $H_0$ measured in the local universe to be consistent with measurements of the cosmic microwave background. However, new high $ell$ polarisation data constrain the sterile neutrino mass to be less than approximately 1 eV in this scenario. Finally, we combine the cosmological bounds on the pseudoscalar model with a Bayesian inference analysis of SBL data and conclude that only a sterile mass in narrow ranges around 1 eV remains consistent with both cosmology and SBL data.
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