Neutrinos from Off-Shell Final States and the Indirect Detection of Dark Matter

TL;DR

This paper analyzes neutrino signals from dark matter annihilation near kinematic thresholds, re-evaluates detection constraints, and establishes model-independent exclusions for certain dark matter masses based on neutrino observations.

Contribution

It introduces a detailed analysis of off-shell neutrino final states in dark matter annihilation and refines indirect detection constraints, including model-independent exclusions.

Findings

Super-Kamiokande provides the most stringent constraints for 60 GeV < mX < mt.

Majorana dark matter with s-channel Z annihilation is excluded for 70 GeV < mX < mW.

Annihilation to tt* can weaken neutrino signals but is negligible in the minimal model.

Abstract

We revisit the annihilation of dark matter to neutrinos in the Sun near the WW and tt kinematic thresholds. We investigate the potential importance of annihilation to WW* in a minimal dark matter model in which a Majorana singlet is mixed with a vector-like electroweak doublet, but many results generalize to other models of weakly-interacting dark matter. We re-evaluate the indirect detection constraints on this model and find that, once all annihilation channels are properly taken into account, the most stringent constraints on spin-dependent scattering for dark matter mass 60 GeV < mX < mt are derived from the results of the Super-Kamiokande experiment. Moreover, we establish the model-independent statement that Majorana dark matter whose thermal relic abundance and neutrino signals are both controlled by annihilation via an s-channel Z boson is excluded for 70 GeV < mX < mW. In some models, annihilation to tt* can affect indirect detection, notably by competing with annihilation to gauge boson final states and thereby weakening neutrino signals. However, in the minimal model, this final state is largely negligible, only allowing dark matter with mass a few GeV below the top quark mass to evade exclusion.