[Paper Review] Neutrino properties from ultra-high energy cosmic neutrinos

Yanqi Huang, Bo-Qiang Ma|arXiv (Cornell University)|Aug 7, 2015

Particle physics theoretical and experimental studies4 citations

TL;DR

This paper investigates ultra-high energy cosmic neutrino (UHECN) flavor ratios using updated neutrino mixing parameters to constrain neutrino properties. It finds that both normal and inverted mass hierarchies are compatible with IceCube data for pion-decay (1:2:0) and muon-damped (0:1:0) sources in the standard oscillation scenario, while the neutron-beam (1:0:0) source is disfavored. In a neutrino decay scenario, the inverted hierarchy and degenerate normal hierarchy cases remain permissible within 3σ limits.

ABSTRACT

Neutrino properties can be constrained by the detection of ultra-high energy cosmic neutrinos (UHECNs). By using the updated global fitting results of neutrino mixing parameters, we present predictions on the neutrino flavor ratios at the Earth from three possibly astrophysical sources. Comparing with the latest IceCube data, we find that the normal hierarchy (NH) and inverted hierarchy (IH) cases from the initial ratios $ϕ_{ν_e}^0:ϕ_{ν_μ}^0:ϕ_{ν_τ}^0=$1:2:0 and 0:1:0 are compatible with the data in the standard neutrino oscillation scenario. We also examine the neutrino flavor ratios in a neutrino decay scenario beyond the standard model, and introduce the special case that two mass eigenstates of neutrinos, i.e., $ν_1$ and $ν_2$, are degenerated. We find that the IH case and the degenerate NH case from the 1:2:0 and 0:1:0 sources are still permissible with the IceCube data within the $3σ$ error range. The general constraints only rely on the neutrino mixing and oscillation framework are also discussed.

Motivation & Objective

• To constrain neutrino mass hierarchy and flavor ratios using ultra-high energy cosmic neutrino (UHECN) data from IceCube.
• To evaluate the compatibility of different astrophysical sources—pion-decay, muon-damped, and neutron-beam—with IceCube's latest flavor ratio measurements.
• To explore the implications of neutrino decay beyond the standard model, particularly in the case of degenerate mass eigenstates ν₁ and ν₂.
• To assess the general constraints on final neutrino flavor ratios based solely on neutrino mixing and oscillation frameworks, independent of source assumptions.

Proposed method

• Utilizes updated global fitting results of neutrino mixing parameters (θ₁₂, θ₂₃, θ₁₃, δ) from recent experiments, including MINOS, Daya Bay, and T2K.
• Applies the Pontecorvo-Maki-Nakawaga-Sakata (PMNS) mixing matrix to calculate flavor transition probabilities during neutrino propagation from source to Earth.
• Evaluates final neutrino flavor ratios at Earth for three initial source ratios: 1:2:0 (pion decay), 0:1:0 (muon-damped), and 1:0:0 (neutron beam).
• Considers a non-standard scenario involving neutrino decay, particularly focusing on the case where ν₁ and ν₂ are degenerate mass eigenstates.
• Performs statistical comparison of theoretical predictions with IceCube's 2015-2016 data, using 3σ confidence intervals to assess compatibility.
• Analyzes the general constraint case where initial flavor ratios and mass eigenstate populations are arbitrary, relying only on mixing parameters to limit final ratios.

Experimental results

Research questions

• RQ1 Are the normal and inverted neutrino mass hierarchies consistent with IceCube's measured UHECN flavor ratios?
• RQ2 How do different astrophysical sources—pion decay, muon-damped, and neutron-beam—contribute to the final observed flavor ratios at Earth?
• RQ3 Can the neutrino decay scenario beyond the standard model accommodate IceCube data, especially in the case of degenerate ν₁ and ν₂ mass eigenstates?
• RQ4 To what extent can the neutrino mixing and oscillation framework alone constrain the final flavor ratios, independent of source assumptions?

Key findings

• The normal hierarchy (NH) and inverted hierarchy (IH) cases are both compatible with IceCube data for initial flavor ratios of 1:2:0 (pion decay) and 0:1:0 (muon-damped) sources within 3σ confidence intervals.
• The neutron-beam source with initial ratio 1:0:0 is disfavored for both NH and IH cases, as its predicted flavor ratios do not overlap with IceCube's 3σ region.
• In the neutrino decay scenario, the IH case and the degenerate NH case (with ν₁ and ν₂ nearly degenerate) remain permissible for 1:2:0 and 0:1:0 sources within 3σ limits.
• The non-degenerate NH case and degenerate NH case from the 1:0:0 source are disfavored by the data, indicating constraints on decay models.
• Even without assuming any specific source, the neutrino mixing and oscillation framework alone imposes strong constraints on final flavor ratios, with 3σ regions in NH and IH cases being nearly identical and covering only a small portion of the ratio triangle.
• The IceCube best-fit point lies outside the general 3σ region, suggesting potential tension with the standard model and possible evidence for new physics beyond neutrino mixing and oscillation.