Neutrino flavor ratios as diagnostic of solar WIMP annihilation

TL;DR

This paper analyzes how solar matter effects influence neutrino flavor ratios from WIMP annihilation in the Sun, proposing that these ratios can help distinguish WIMP models and infer neutrino properties.

Contribution

It provides a detailed analytical and realistic treatment of neutrino flavor propagation from the Sun's core to Earth, including matter effects, non-adiabatic transitions, and CP phase considerations.

Findings

Flavor ratios differ significantly between WIMP annihilation channels.

Resonance effects of matter influence flavor propagation even for small  values.

Measuring flavor ratios can help discriminate WIMP models and infer neutrino parameters.

Abstract

We consider the neutrino (and antineutrino) flavors arriving at Earth for neutrinos produced in the annihilation of weakly interacting massive particles (WIMPs) in the Sun's core. Solar-matter effects on the flavor propagation of the resulting $\agt$ GeV neutrinos are studied analytically within a density-matrix formalism. Matter effects, including mass-state level-crossings, influence the flavor fluxes considerably. The exposition herein is somewhat pedagogical, in that it starts with adiabatic evolution of single flavors from the Sun's center, with $\theta_{13}$ set to zero, and progresses to fully realistic processing of the flavor ratios expected in WIMP decay, from the Sun's core to the Earth. In the fully realistic calculation, non-adiabatic level-crossing is included, as are possible nonzero values for $\theta_{13}$ and the CP-violating phase $\delta$. Due to resonance enhancement in matter, nonzero values of $\theta_{13}$ even smaller than a degree can noticeably affect flavor propagation. Both normal and inverted neutrino-mass hierarchies are considered. Our main conclusion is that measuring flavor ratios (in addition to energy spectra) of $\agt$ GeV solar neutrinos can provide discrinination between WIMP models. In particular, we demonstrate the flavor differences at Earth for neutrinos from the two main classes of WIMP final states, namely $W^+ W^-$ and 95% $b \bar{b}$ + 5% $\tau^+\tau^-$. Conversely, if WIMP properties were to be learned from production in future accelerators, then the flavor ratios of $\agt$ GeV solar neutrinos might be useful for inferring $\theta_{13}$ and the mass hierarchy.