On the robustness of IceCube’s bound on sterile neutrinos in the presence of non-standard interactions

Eur. Phys. J. C (2019) 79:70 https://doi.org/10.1140/epjc/s10052-019-6595-9 Regular Article - Theoretical Physics On the robustness of IceCube’s bound on sterile neutrinos in the presence of non-standard interactions Arman Esmailia , Hiroshi Nunokawab Departamento de Física, Pontifícia Universidade Católica do Rio de Janeiro, C. P. 38097, Rio de Janeiro 22451-900, Brazil Received: 17 November 2018 / Accepted: 12 January 2019 © The Author(s) 2019 Abstract The mixing parameters of sterile neutrino(s) preferred by the MiniBooNE and LNSD experiments are in strong tension with the exclusion limit from the IceCube experiment. Recently it has been claimed that by considering the non-standard neutrino interactions (NSI) in addition to the sterile neutrino, the IceCube’s limit can be relaxed and the tension can be reconciled; a baroque scenario as it has been called. We will show that this claim is just an artifact originating from the energy cuts of the chosen datasets. Contrary to the claim, by turning on the NSI and fixing the NSI parameters to the proposed values, not only the IceCube’s limit on sterile neutrino cannot be alleviated, but in fact the tension will be aggravated (or at least keeps its strength). To this aim, an analysis of the IceCube’s atmospheric neutrino data in the full energy range is crucial. 1 Introduction Currently, almost all the neutrino data can be explained consistently in the 3ν formalism, consisting of three active neutrino flavors and the corresponding mixing parameters (for a global fit to all the available data see [1–3]). However, there are still some anomalies, coming from the electron neutrino appearance experiments, namely, the LSND [4] and MiniBooNE [5] experiments, which indicate the existence of extra neutrino states, the so-called sterile neutrinos, with the mass ∼ O(1) eV. In particular, the recent update from the MiniBooNE experiment [6], which combines the νe and ν̄e appearance data, reports an excess of 4.8σ in the low energy range that can be increased to 6.1σ if combined with the LSND data. This excess can be interpreted in the 3 + 1 scenario (3 active + 1 sterile neutrino state) with Δm 241 ∼ O(1) eV2 and sin2 2θeμ  10−2 . The a e-mail: allowed region in the (sin2 2θeμ , Δm 241 ) plane can be found in [6]. The main obstacle in a happy interpretation of the LSND/MiniBooNE excess in terms of the sterile neutrinos is the strong tension with the disappearance data including MINOS/MINOS+ [7] and IceCube [8] experiments (for a global status of the sterile neutrino mixing from various experiments see [9,10]). Among these the IceCube’s limit has a different nature: while the MINOS experiment is sensitive to the sterile neutrino mixing through an averaged effect over the long baseline, the IceCube sensitivity originates from a resonance effect, an amplification of the ν̄μ → ν̄s oscillation probability (or νμ → νs for Δm 241 < 0) for atmospheric neutrinos crossing the Earth in the ∼ TeV energy range. The possibility of exploring the active-sterile neutrino mixing by looking at the energy and zenith angle distributions of the high energy atmospheric neutrinos has been proposed in [11,12] (see also [13]). By the realization of the IceCube detector, as the first km3 -volume neutrino telescope which is able to detect ∼ TeV atmospheric neutrinos, this possibility has been studied in detail: the limit on eV-scale sterile neutrinos has been derived using the data collected during the construction phase of the IceCube [14] and it has been shown that few-years worth of the IceCube data can exclude completely the preferred region by LSND and MiniBooNE [15]. The effect of the various mixing parameters in the 3 + 1 scenario has been studied in [15] and the search strategy generalized to the cascade event topology in [16] (see also [17–20] for further analyses). Finally the IceCube collaboration published the result of the sterile neutrino analysis [8], considering one-year muon-track data with the reconstructed muon energy proxy in the range 400 GeV − 20 TeV, demonstrating the exclusion of the preferred parameter space region by the appearance experiments (to be precise, constraining the angle θ24 in the 3 + 1 scenario). b e-mail: 0123456789().: V,-vol 123 70 Page 2 of 10 Another new physics scenario that can be probed by the high energy atmospheric neutrinos observed by the IceCube is the non-standard neutrino interactions. This possibility has been proposed and used to derive the most stringent bound on the NSI parameters (the εμτ and εμμ − ετ τ ) in [21], with consistent results in [22,23] (see [24] for bounds on the NSI parameters from the global analysis of oscillation data). Recently it has been proposed in [25] that the addition of non-standard neutrino interaction to the 3 + 1 picture can relax the limit of IceCube on sterile neutrinos and reconcile the appearance and disappearance discrepant results. The same claim has been repeated in a more recent work [26] which analyses the data of MINOS+ and IceCube, including the DeepCore data, and concludes that a combination of the charged-current and neutral-current NSI can relax the limits of both experiments. In this framework, the charged-current NSI is required for the relaxation of the MINOS+ limit (a D , has been assumed) while the nonzero detector NSI, εμμ neutral-current NSI parameters (nonzero εμμ , ετ τ and εss ) will, pretendedly, loosen the IceCube’s limits. The IceCube data analyzed in [26] consists of the publicly available sterile search data1 [8] with the muon energy2 ∈ [501 GeV, 10 TeV] and the DeepCore oscillation data3 [28] with the muon energy range [6, 56] GeV. In this paper we will argue that in fact the apparent relaxation of the IceCube’s limit on the sterile neutrino in the (3 + 1)+NSI scenario originates from the negligence of the [56, 500] GeV energy range and has no physical rationale behind. It should be emphasized that although the recent IceCube publicization of data on atmospheric neutrinos does not include the [56, 500] GeV energy range, older data are available, such as the IC-79 [29] and IC-40 [30], which cover this energy range and do not show any significant deviation from the 3ν framework expectation. Considering this energy range, contrary to the claim in [25,26], the limit on sterile neutrino from IceCube will be stronger in the (3 + 1)+NSI scenario or will keep the strength, depending on the quality of the data in the [56, 500] GeV energy range. To this aim, actually, a simple oscillation probability calculation is enough to manifest the argument. The paper is organized as follows: In Sect. 2 we summarize the main features of the atmospheric muon (anti-)neutrino oscillation in the (3 + 1)+NSI scenario and describe our assumptions. In Sect. 3 we discuss in detail, based mainly on oscillation probabilities, why the addition of NSI to the 3 + 1 model cannot help to the reconciliation of the LSND/MiniBooNE and IceCube tension. Finally, in Sect. 4 (...truncated)