A model for neutrino anomalies and IceCube data

Abstract

We interpret the neutrino anomalies in neutrino oscillation experiments and the high energy neutrino events at IceCube in terms of neutrino oscillations in an extension of the standard model where three sterile neutrinos are introduced so as to make two light neutrinos to be Pseudo-Dirac particles and a light neutrino to be a Majorana particle. Our model is different from the so-called 3 + n model with n sterile neutrinos suggested to interpret short baseline anomalies in terms of neutrino oscillations. While the Pontecorvo-Maki-Nakagawa-Sakata (PMNS) matrix in 3 + n model is simply extended to n × n unitary matrix, the neutrino mixing matrix in our model is parameterized so as to keep the 3 × 3 PMNS mixing matrix for three active neutrinos unitary.There are also no flavor changing neutral current interactions leading to the conversion of active neutrinos to sterile ones or vice versa. We derive new forms of neutrino oscillation probabilities containing the new interference between the active and sterile neutrinos which are characterized by additional new parameters ∆m 2 and θ. Based on the new formulae derived, we show how the short baseline neutrino anomalies can be explained in terms of oscillations, and study the implication of the high energy neutrino events detected at IceCube on the probe of pseudo-Dirac neutrinos. New phenomenological effects attributed to the existence of the sterile neutrinos are discussed. The observation of neutrino oscillations in the atmospheric neutrino 1 Super-Kamiokande [3], the solar neutrino 2 SNO [5], and the reactor neutrino Daya Bay[6] and RENO [7] 3 experiments is one of big discoveries in particle physics since 90's. It implies that neutrinos are massive particles and that the three flavor neutrinos ν e , ν µ , ν τ are mixtures of neutrinos with definite masses ν i (with i = 1, 2, ...). Although neutrino oscillations among three active neutrino flavors have been confirmed by the analysis based on the experiments mentioned above, there exist several anomalies which are unexpected results coming from short baseline (SBL) experiments such as the reactor antineutrino anomaly [9], the Gallium solar anomaly [10,11], and the Liquid Scintillator Neutrino Detector (LSND) anomaly [12] (including MiniBooNE anomaly [13]). To resolve those neutrino anomalies in terms of neutrino oscillation, it is required to introduce at least one additional squared-mass difference, ∆m 2 SBL , which is much larger than ∆m 2 Sol and ∆m 2 Atm [9]. This result suggests indication in favor of the possible existence of eV-mass sterile neutrino.Apart from the anomalous results in accelerator and reactor based neutrino experiments favoring the existence of light sterile neutrino, IceCube experiments [14] announced the observation of vey high energy neutrino events. The study for the track-to shower ratio of the subset with energy above 60 TeV coming from IceCube has shown that the events are consistent with the hypothesis that cosmic neutrinos have been seen even though their origin and propagation are stil...

Challenge to anomalous phenomena in solar neutrino

“…If the anomalous phenomena are interpreted in terms of neutrino oscillations, it may suggest the presence of other types of light neutrinos called sterile neutrinos that do not have weak interactions. 1 An attempt to explain the SBL anomalies has been proposed in a framework of neutrino oscillation [25]. Moreover, in the same framework for neutrino oscillation the experimental results on high energy neutrinos released from IceCube [26][27][28] could be interpreted 2 as new oscillation effects [25,30,31].…”

“…The goal of this work is to study for a theoretical understanding of the solar neutrino tension why solar neutrinos at SNO, SK, and Borexino experiments appear to mix differently from reactor antineutrinos at KamLAND, despite that both neutrinos are sensitive to the same oscillation parameters in the 3νSF. To do that, first, based on an extended theory with light sterile neutrinos added [25] we derive a general transition probability between the massive neutrinos that a flavor eigenstate ν α becomes flavor eigenstate ν β with α, β = e, µ, τ , that can also have a potential for explaining both the anomalous phenomena and ultra-high energy neutrino events at IceCube, simultaneously. 3 Second, we re-examine the MSW matter effects in our theoretical framework and suggest a solution to the solar neutrino tension with a so-called composite matter effect that causes a neutrino flavor change with new oscillatory terms containing ∆m 2 ABL O(10 −11 ) eV 2 optimized at astronomical-scale baseline (ABL) ( L es = 149.6 × 10 6 km, earth-sun distance) oscillation experiments together with the MSW matter effect.…”

“…In the basis of interaction eigenstates, ψ L ≡ (ν L S c R ) T , where active neutrinos are in the up-stairs and sterile neutrinos are in the down-stairs, the most general renormalizable Lagrangian for neutrinos reads in the charged lepton basis at low energies [25]…”

“…, which preserves norm and thus probability amplitude, and choose the 6×6 unitary neutrino transformation matrix as [25,30,31]…”

“…To resolve a tension between the mass-squared differences of solar and reactor neutrinos in eq. 2.17, as well as to accommodate an eV sterile neutrino for a possible solution to the SBL anomalies [25] and ultra-high energy neutrino events at the IceCube detector [25,30,31,[46][47][48], we assume…”