[Paper Review] General Upper Bound on the Dark Matter Total Annihilation Cross Section

J. F. Beacom, Nicole F. Bell+1 more|arXiv (Cornell University)|Aug 3, 2006

Dark Matter and Cosmic Phenomena23 citations

TL;DR

This paper establishes a general upper bound on the total dark matter annihilation cross section by analyzing cosmic diffuse neutrinos, which are the least detectable final states. By comparing the predicted neutrino flux from dark matter annihilation to the observed terrestrial atmospheric neutrino background, the authors derive a stringent constraint that is significantly stronger than the unitarity bound at relevant masses, ruling out significant modifications to dark matter halos and offering a path to improvement by a factor of 10–100 with current experiments.

ABSTRACT

We consider dark matter annihilation into Standard Model particles and show that the least detectable final states, namely neutrinos, define an upper bound on the total cross section. Calculating the cosmic diffuse neutrino signal, and comparing it to the measured terrestrial atmospheric neutrino background, we derive a strong and general bound. Our bound is much stronger than the unitarity bound at the most interesting masses, shows that dark matter halos cannot be significantly modified by annihilations, and can be improved by a factor of 10--100 with existing neutrino experiments.

Motivation & Objective

• To establish a general upper limit on the total dark matter annihilation cross section independent of specific models.
• To address the challenge of detecting dark matter through its least observable final states—neutrinos—by leveraging cosmic diffuse neutrino backgrounds.
• To improve existing constraints, particularly in the mass range relevant for indirect dark matter searches.
• To assess the potential for future improvements using existing neutrino detection technologies.

Proposed method

• Modeling the cosmic diffuse neutrino background from dark matter annihilation into Standard Model particles.
• Comparing the predicted neutrino flux from dark matter annihilation to the measured terrestrial atmospheric neutrino background.
• Using the observed atmospheric neutrino flux as a benchmark to set an upper limit on the dark matter annihilation cross section.
• Applying this comparison across a range of dark matter masses to derive a general, model-independent bound.
• Evaluating the sensitivity of current and near-future neutrino experiments to improve the bound by a factor of 10–100.

Experimental results

Research questions

• RQ1 What is the strongest possible upper bound on the total dark matter annihilation cross section that can be derived from neutrino final states?
• RQ2 How does the bound derived from cosmic diffuse neutrinos compare to the unitarity bound across relevant dark matter masses?
• RQ3 To what extent can dark matter halos be modified by self-annihilations, given the derived cross section limit?
• RQ4 Can existing neutrino experiments improve the bound by a factor of 10–100, and if so, under what conditions?

Key findings

• The derived upper bound on the dark matter annihilation cross section is significantly stronger than the unitarity bound at the most relevant dark matter masses.
• The bound is general and model-independent, relying only on the fact that neutrinos are the least detectable final states.
• Dark matter halos cannot be significantly modified by self-annihilations due to the stringent cross section limit.
• The bound can be improved by a factor of 10–100 using existing neutrino detection experiments, offering a promising path for future constraints.