Using Secondary Tau Neutrinos to Probe Heavy Dark Matter Decays in Earth

TL;DR

This paper explores how secondary tau neutrinos from heavy dark matter decays within Earth can be detected by IceCube, revealing constraints on dark matter properties at energies above PeV.

Contribution

It introduces an updated model of dark matter capture and decay, highlighting the significance of tau neutrino regeneration and energy loss effects at ultra-high energies.

Findings

IceCube can probe dark matter decays above PeV energies.

Tau neutrino regeneration extends detection distances.

Dark matter cross sections constrained are in tension with direct detection bounds.

Abstract

Dark matter particles can be gravitationally trapped by celestial bodies, motivating searches for localized annihilation or decay. If neutrinos are among the decay products, then IceCube and other neutrino observatories could detect them. We investigate this scenario for dark matter particles above $m_{\chi} \gtrsim$ PeV producing tau neutrino signals, using updated modeling of dark matter capture and thermalization. At these energies, tau neutrino regeneration is an important effect during propagation through Earth, allowing detection at distances far longer than one interaction length. We show how large energy loss of tau leptons above $\sim$ PeV drives a wide range of initial energies to the same final energy spectrum of "secondary" tau neutrinos at the detector, and we provide an analytic approximation to the numerical results. This effect enables an experiment to constrain decays that occur at very high energies, and we examine the reach of the IceCube high-energy starting event (HESE) sample in the parameter space of trapped dark matter annihilations and decays above PeV. We find that the parameter space probed by IceCube searches would require dark matter cross sections in tension with existing direct-detection bounds.