[Paper Review] Signatures of sterile neutrino mixing in high-energy cosmic neutrino flux

A. Donini, Osamu Yasuda|ArXiv.org|Jun 18, 2008

Particle physics theoretical and experimental studies7 citations

TL;DR

This paper investigates signatures of a (3+1) sterile neutrino scenario in high-energy cosmic neutrino fluxes from distant astrophysical sources, focusing on flavor ratios despite theoretical uncertainties in neutrino energy spectra. It shows that the νμ−ντ ratio is robust against these uncertainties and thus the optimal observable to detect sterile neutrino mixing, offering a viable path to probe four-neutrino models with future neutrino telescopes.

ABSTRACT

Even after the negative result by the MiniBooNE experiment, we can still have a (3+1)-scheme with one sterile neutrino whose mixing lies within the allowed region by MiniBooNE. In this note we discuss the possible effects of such a scheme on the flavor ratio of high-energy cosmic neutrinos from cosmologically distant astrophysical sources. It is shown that in principle there is still a chance to observe deviation from the standard three flavor scenario in the flavor ratio of the high-energy cosmic neutrinos. It is proposed to see the energy spectrum to cope with the theoretical uncertainties which were recently pointed out by Lipari, Lusignoli and Meloni. It is emphasized that the $ν_μ-ν_τ$ ratio is relatively insensitive to the theoretical uncertainties and therefore this ratio is the key ingredient to look for the signatures of the sterile neutrino scheme. Although the statistics of data from one source in the next generation of neutrino telescopes are estimated not to be sufficient to distinguish the three and four family schemes, if we can gain statistics by, e.g., summing over data from many sources, then it might be possible to have a signature for the (3+1)-scheme.

Motivation & Objective

• To assess the detectability of a (3+1) sterile neutrino scenario in high-energy cosmic neutrino fluxes from distant sources.
• To address theoretical uncertainties in neutrino energy spectra that hinder flavor ratio measurements, as highlighted by Lipari et al.
• To identify the most robust flavor ratio observable for distinguishing three- from four-neutrino mixing scenarios.
• To evaluate the potential of future neutrino telescopes to detect sterile neutrino signatures through statistical combination of data from multiple sources.

Proposed method

• Uses analytical second-order expansions in small mixing angles (θ13, θ14, θ24, η = π/4 − θ23) and energy-dependent spectral corrections (ε(Eν) = 2 − λ(Eν)) to model neutrino fluxes.
• Derives analytic expressions for neutrino fluxes Φμ, Φτ, Φe, and Φs at the detector in the (3+1) scheme, including CP-violating phases δ1 and δ3.
• Evaluates flavor ratios R_eμ = (νe + ν̄e)/(νμ + ν̄μ) and R_τμ = (ντ + ν̄τ)/(νμ + ν̄μ) under the (3+1) model with parameters constrained by Donini et al. (2007).
• Analyzes energy dependence of fluxes and ratios, comparing sensitivity to theoretical uncertainties in the source energy spectrum.
• Compares the robustness of R_eμ and R_τμ to spectral uncertainties, identifying R_τμ as less sensitive.
• Proposes combining data from multiple astrophysical sources to enhance statistical power for detecting (3+1) scheme deviations.

Experimental results

Research questions

• RQ1 Can the (3+1) sterile neutrino scenario produce observable deviations in high-energy cosmic neutrino flavor ratios despite theoretical uncertainties?
• RQ2 Which flavor ratio—R_eμ or R_τμ—is most robust against uncertainties in the neutrino energy spectrum?
• RQ3 To what extent can future neutrino telescopes distinguish three- from four-neutrino mixing using flavor ratios?
• RQ4 How do CP-violating phases and mixing angles (especially θ34) influence the detectability of sterile neutrinos in cosmic fluxes?
• RQ5 What is the role of statistical combination of data from multiple sources in enhancing sensitivity to sterile neutrino signatures?

Key findings

• The νμ−ντ ratio (R_τμ) is significantly less sensitive to uncertainties in the neutrino energy spectrum than R_eμ, making it the optimal observable for detecting sterile neutrino mixing.
• R_eμ is strongly affected by spectral uncertainties and cannot reliably distinguish three- from four-family mixing scenarios.
• The (3+1) scheme can produce measurable deviations in flavor ratios, but only if R_τμ is used as the primary observable.
• Even with limited statistics from a single source, the R_τμ ratio remains a viable probe due to its insensitivity to spectral modeling errors.
• The presence of sterile neutrinos affects the flux ratios primarily through θ34 and θ24, but θ34 is constrained to ≤35°, limiting the signal strength.
• Combining data from multiple astrophysical sources can overcome statistical limitations and make detection of the (3+1) scheme feasible with next-generation neutrino telescopes.