Flavor Ratios of Astrophysical Neutrinos: Implications for Precision Measurements

TL;DR

This paper analyzes how small deviations in neutrino mixing parameters and initial flavor ratios affect the observed flavor ratios of astrophysical neutrinos, emphasizing the importance of including second order corrections for accurate interpretations.

Contribution

It provides a detailed expansion of flavor-fluxes considering small parameters and explores the impact of initial flavor deviations on observational data, highlighting potential pitfalls in current analyses.

Findings

Second order corrections can dominate first order terms in flavor ratio calculations.

Small deviations in initial flavor ratios significantly alter observed ratios at Earth.

Neglecting initial flavor deviations can lead to incorrect inferences of neutrino mixing parameters.

Abstract

We discuss flavor-mixing probabilities and flavor ratios of high energy astrophysical neutrinos. In the first part of this paper, we expand the neutrino flavor-fluxes in terms of the small parameters U_{e3} and pi/4 - theta_{23}, and show that there are universal first and second order corrections. The second order term can exceed the first order term, and so should be included in any analytic study. We also investigate the probabilities and ratios after a further expansion around the tribimaximal value of sin^2 theta_{12} = 1/3. In the second part of the paper, we discuss implications of deviations of initial flavor ratios from the usually assumed, idealized flavor compositions for pion, muon-damped, and neutron beam sources, viz., (1 : 2 : 0), (0 : 1 : 0), and (1 : 0 : 0), respectively. We show that even small deviations have significant consequences for the observed flavor ratios at Earth. If initial flavor deviations are not taken into account in analyses, then false inferences for the values in the PMNS matrix elements (angles and phase) may result.