Does dark matter annihilate quicker in the Milky Way?

June 23, 2017, Tata Institute of Fundamental Research
The annihilation rates have a signature non-monotonic velocity dependence over and above the resonances, e.g., for DM mass larger than 4 TeV the galactic annihilation rate (solid line) exceeds that in clusters (dashed line) and dwarf galaxies (dot- dashed line). Credit: Anirban Das, Basudeb Dasgupta

Researchers at the Tata Institute of Fundamental Research in Mumbai have proposed a theory that predicts how dark matter may be annihilating much more rapidly in the Milky Way, than in smaller or larger galaxies and the early Universe.

Anirban Das, with his advisor Dr. Basudeb Dasgupta, pursued this possibility because almost all observations made so far indicate no signals of anywhere—except the tantalizing signals from the Milky Way seen by the PAMELA and AMS02 detector and the Fermi gamma ray telescope. If the dark matter origin of these signals stands further scrutiny and signals aren't seen from anywhere except the Milky Way, their theory would explain why the Milky Way appears to be special.

In the enchanting night sky, with myriad galaxies and stars, what we see is only about 20% of all the matter in the Universe. The remaining is in the form of a non-luminous and exotic form of matter that we know little about. This so-called dark matter has been the object of intense scientific exploration in the last few decades. According to many popular theories, dark annihilate at the same rate in both small and large astronomical bodies and at all times in the Universe.

This new study published in the journal Physical Review Letters on 23rd June 2017, shows that this peculiar behaviour of the annihilation rate, in that it is not the same everywhere, stems from the symmetries of the annihilating .

Further, it would predict that dark matter is made of more than one particle and interacts through a yet-undiscovered low-mass particle. The absence of dark matter annihilation signals outside the Milky Way could be a crucial hint towards this richer theory of , which will be tested by future observations.

Explore further: 3 knowns and 3 unknowns about dark matter

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Da Schneib
not rated yet Jun 23, 2017
Meh, this is fine tuning with all the warts. Without a real journal reference (and simply linking to Physical Review Letters prevents any search of arXiv by title or content) there is no way to evaluate this claim. This article is clickbait without that.
Benni
1.8 / 5 (5) Jun 23, 2017
Meh, this is fine tuning with all the warts. Without a real journal reference (and simply linking to Physical Review Letters prevents any search of arXiv by title or content) there is no way to evaluate this claim. This article is clickbait without that.


Admit it Schneibo, this quote is the only reason you don't like it:

"Anirban Das, with his advisor Dr. Basudeb Dasgupta, pursued this possibility because almost all observations made so far indicate no signals of dark matter annihilation anywhere."


Yeah, "no signals of dark matter........."

RNP
4.4 / 5 (7) Jun 24, 2017
@Da Schneib
Actually, an open access copy of the paper can be found here; https://arxiv.org...4606.pdf
(it is in the high energy physics section of arXiv).
MadScientist72
5 / 5 (1) Jun 24, 2017
no signals of dark matter annihilation anywhere

How are you supposed to detect signals of something being annihilated when you can't detect signals for the thing itself? Even if you did detect SOMETHING getting annihilated how could you say with any certainty that it was dark matter?
Da Schneib
not rated yet Jun 24, 2017
Hahaha, thanks @RNP, without a title I couldn't figure how to search on it and be sure I'd found the right thing!

Now for a litte reading...
Da Schneib
not rated yet Jun 24, 2017
OK, well that explains that. This article is badly written; from reading the paper it's apparent that this effect isn't restricted to galaxies "like" the Milky Way, but should be apparent in all galaxies, with diminishing intensity by size. It shouldn't be apparent at the galaxy cluster level, and it also shouldn't be evident in early times like providing a signature in the CMB; the effect only happens for medium-velocity DM collisions, which are prevalent at the galactic scale and at late times. Any DM CMB signature wouldn't be due to this effect, at least the article got that right.

Maybe someone can write a better article about this. @RNP, I'd welcome your comments on my analysis.
Da Schneib
not rated yet Jun 24, 2017
no signals of dark matter annihilation anywhere

How are you supposed to detect signals of something being annihilated when you can't detect signals for the thing itself? Even if you did detect SOMETHING getting annihilated how could you say with any certainty that it was dark matter?
Thing about this is, we have the SM. Now that we've confirmed the Higgs, we have a pretty good set of scattering matrices and we can predict where we ought to see peaks in the production of various particles, and peaks in the EM spectrum for certain types of interactions between the known particles including annihilation. The signatures are quite distinctive, and you can think of them as the same sorts of spectra in the EM that tell us the chemical compositions of stars, but somewhat less complex because there are less types of particles than there are of atoms. As a result, looking for peaks that can't be explained by SM particles is a pretty good way to find if there's DM.
[contd]
Da Schneib
not rated yet Jun 24, 2017
[contd]
We've looked for these sorts of signatures, but so far haven't found any. However, we haven't categorically combed both the particle and EM sectors for anomalous peaks, particularly not from satellites, which is where you've got the best probability of finding this kind of evidence. It's kind of like being at the point of understanding that we can find the chemical elements in stars using EM spectra, but not having looked at very many stars with spectrographs yet.

Worth mentioning that there is a cause for the gravitational anomalies in both galaxy rotations and galaxy cluster dynamics. So there has to be something doing it, and the best guess is DM since we can't find anything in GR that accounts for it and is consistent with our experiments.

No point in criticizing a theory until you have enough data to evaluate it, yes? Good question, though.
krizo888
not rated yet Jul 12, 2017
neophyte here - could dark matter just be immense patches of particles ? -- either neutrons, positrons or neutrinos?

since (H) is the most abundant chemical substance in the Universe -and the most common isotope of hydrogen, protium 1H has one proton and no neutrons. ...and the weak nuclear force is always shedding particles ...and.. well...they have to gather somewhere ...

Nik_2213
not rated yet Aug 08, 2017
Unlikely to be 'free' neutrons. Those have a short half-life, 10~~15 mins depending on measurement technique. And, yes, that decay and that variation remain 'head-scratchers' ...

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