For a project I am currently reading into indirect detection of Dark Matter via gamma-rays from DM subhalo's. I understand that there is a possibility of DM annihilating with each other in these subhalo's to produce the gamma-rays. However, whilst reading a certain article they mentioned hadronic annihilation channels ($b\bar{b}$ & $\tau^+\tau^-$ in this case) producing a DM gamma-ray flux. I am not quite sure what is meant by this. Does DM possible decay into a bottom & anti-bottom quark which then annihilates to produce gamma-rays or do they mean something different?

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    $\begingroup$ why don't you give a link with the statements so people do not have to guess what they are. They are probably talking of specific annihilation Feynman diagrams for the proposed WIMP particles ( wimp+antiwimp--> into bs +bbars $\endgroup$
    – anna v
    Commented Jan 19, 2019 at 16:05
  • $\begingroup$ arxiv.org/abs/1611.03503, Its in the first 6 lines of section 2.2 $\endgroup$
    – Smitty
    Commented Jan 19, 2019 at 17:03

1 Answer 1


The link is referring to WIMPS and models them as the constituents of dark matter:

Weakly interacting massive particles (WIMPs) are hypothetical particles that are thought to constitute dark matter. There exists no clear definition of a WIMP, but broadly, a WIMP is a new elementary particle which interacts via gravity and any other force (or forces), potentially not part of the standard model itself, which is as weak as or weaker than the weak nuclear force, but also non-vanishing in its strength. A WIMP must also have been produced thermally in the early Universe, similarly to the particles of the standard model according to Big Bang cosmology, and usually will constitute cold dark matter.

In general, particle physics has particles and antiparticles, and the same will be true for WIMPs. It is assumed that in primordial times an equal amount of particles and antiparticles were generated at the end of inflation, in this chronology and before the formation of protons ( when baryon antibaryon asymmetry becomes evident,this is still one of the problems with the standard model) The models for WIMPS are speculative, but they are within the quantum field theory, ones that describe elementary particle interactions using Feynman diagrams, and thus able with certain hypothesis to estimate their crossection for scattering and annihilating on each other and generating the usual standard model of physics particles. In fig6.1 there is a generic Feynman diagram of how the weakly interacting WIMPs can be produced and interact with strongly and electromagnetically interacting particles.

Wimps because they interact weakly do not form usual matter but remain as halos around clusters of galaxies and galaxies, but they do interact and these interactions modeled give the gamma rays that might be detected .

Does DM possible decay into a bottom & anti-bottom quark which then annihilates to produce gamma-rays or do they mean something different?

Decay means a particle, even at rest, can go into other, smaller mass particles , its mass is larger than the sum of the masses it decays into. If it is a WIMP, depending on the model, it is a very slow process, that is what the W (eak) stands for. Scattering interaction may statistically be much more probable in the dark matter density, and that is what the models use.

If you substitute DM annihilation for decay, yes, then the tau has a channel decaying to a pi0 , which will give two gammas. Something similar is true for the b.

These decays are used in the models that try to predict gamma distributions from dark matter halos, and also the subsequent usual interactions of the decay products , electromagnetic and strong,once the b and taus have been created.

  • $\begingroup$ So you mentioned substituting DM annihilation for decay in the second last paragraph, but does that mean the product of DM annihilation in this case would be bottom quarks (or taus) instead of photons? $\endgroup$
    – Smitty
    Commented Jan 20, 2019 at 7:06
  • $\begingroup$ @Smitty depending on the model used for the WIMPS, which would be an extension of the standard model, there will be all the possible decay channels hadronic and electromagnetic quark+quark_bar , lepton +lepton _bar. The b and tau are interesting because they have gamma producing channels. it depends on the model, which will give the probabilities of coupling to the various flavors , which will make them dominant in the annihilation diagrams. $\endgroup$
    – anna v
    Commented Jan 20, 2019 at 7:31
  • $\begingroup$ Ah I see, thanks, I was not yet familiar with annihilation producing products that were not photons $\endgroup$
    – Smitty
    Commented Jan 20, 2019 at 7:42

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