I'm now at a cosmology conference:
https://indico.cern.ch/event/736594/overview

One reason to go to a conference is to hear about interesting things one
might have missed. For me, probably the most interesting talk was the penultimate one, an update on these publications concerning a novel
dark-matter candidate:

https://arxiv.org/abs/1202.0560
https://arxiv.org/abs/1311.1627 http://iopscience.iop.org/article/10.1088/1742-6596/496/1/012023 https://arxiv.org/abs/1801.04206

There are many connections between particle physics and astronomy, but
this is closer than most, is a really novel idea, makes clear
predictions, explains very many (otherwise not closely related) things
with a simple idea, and has already had some predictions confirmed.


While I've been to other conferences which covered a wide range of
topics, at this one there were intentionally no sessions on specific
topics, but, say, a talk on observational astronomy could be followed by
one on theoretical particle physics.

I can't write a summary here, of course, but one general theme is that
while large-scale cosmology is more or less solved, it is becoming even
more clear that many things about galaxies, particularly dwarf galaxies,
are not understood, and it is unclear which of many options is the way
forward. One aspect of this is dark matter, and both the lack of direct
(or indirect) detections as well as the discovery of a light Higgs seems
to be swinging the pendulum away from WIMPs as dark matter to other
ideas. Also, it might turn out that more than one of the alternatives
to WIMPs is correct.

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Le 27/10/2018 � 18:50, Phillip Helbig (undress to reply) a �crit :

I'm now at a cosmology conference: https://indico.cern.ch/event/736594/overview

One reason to go to a conference is to hear about interesting things one might have missed. For me, probably the most interesting talk was the penultimate one, an update on these publications concerning a novel dark-matter candidate:

https://arxiv.org/abs/1202.0560
https://arxiv.org/abs/1311.1627 http://iopscience.iop.org/article/10.1088/1742-6596/496/1/012023 https://arxiv.org/abs/1801.04206

Those papers do not show any physical evidence. The common author in all
papers is Jarah Evslin, working in Peking.

https://arxiv.org/abs/1202.0560 says:

We propose a model of dark matter: galaxy-sized 't Hooft-Polyakov
magnetic monopoles

OK. The only evidence is presented in:
https://arxiv.org/abs/1801.04206. This paper shows a simulation for
"Spiked monopoles" done in some computer. According to the authors:
<quote>
Dark matter halos grow by merging. This merging requires them to be
attractive, but the simplest manifestation of monopole dark matter is repulsive.
<end quote>

!!!

<quote>
If the magnetic repulsion is sufficiently weak, then it can be overcome
by gravity. However fitting parameters in the simplest model [1] one
finds that v � 1014 GeV and so the magnetic repulsion is stronger than gravitational attraction by nearly 10 orders of magnitude. In the spiked monopole model, the gravitational repulsion is reduced. The crudeness of
our numerical simulations and initial conditions makes it difficult to
quantify the repulsion, however it clearly is not reduced by the
required 10 orders of magnitude.
<end quote>
------------------------------------------------------------------ http://iopscience.iop.org/article/10.1088/1742-6596/496/1/012023 https://arxiv.org/abs/1311.1627

Same author, slightly different presentation, similar arguments. Both
papers are almost the same.

<quote>
Unfortunately these monopoles repel and so the charge Q > 1 halos are
unstable. This may rule out our model. Then again, protons repel but
visible matter is mostly made of protons, as the repulsion at small
distances is canceled by neutrons and at large distances is screened by electrons. The monopoles only repel at long distances. So what are the
analogs of the electrons? Electrons carry the opposite charge from
protons but cannot annihilate with protons as they carry a flavor
quantum number and the lightest state for a decay product, the neutron,
is too massive for the decay to be kinematically allowed. Similarly such
a flavor quantum number for the monopoles is an automatic consequence of
our fermionic couplings. The masses of the various flavors of monopoles
can be adjusted by choosing the Yukawa couplings. We propose to include
light antimonopoles of a different flavor which screen the long distance repulsion of our monopoles. If such a screening cannot be made to work,
our proposal will be excluded.
<end quote>

Let's see then...

They have to first find out the "electrons" that would screen out the
repulsion between those galaxy sized monopoles.

All this is interesting, yes, but it is very difficult to gauge if there
is any connection with reality at this stage. Mathematics is an infinite forest, and it is very easy to lose your way in the equation undergrowth...

Obviously too, I am in NO WAY able to follow precisely those papers, and
can only look at the conclusions.

jacob

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In article <pr56ue$4hp$[email protected]>, jacobnavia
<[email protected]> writes:

Those papers do not show any physical evidence.

Right. If they did, they would be reporting a dark-matter detection,
not discussing a candidate. So, to first order, this is another
candidate like many others: WIMPs, MACHOs, PBHs, fuzzy dark matter, self-interacting dark matter, superfluid dark matter, etc.

The common author in all
papers is Jarah Evslin,

Right.

working in Peking.

Not any more, though still in China. While there might be some examples
of people from the West working in China because they couldn't get any
academic job elsewhere (I have met some), Evslin is definitely not one
of those. He is extremely knowledgeable about both astronomy and
particle physics. This is also a rare combination (not counting people
who work on BBN, inflation, etc, which is mainly particle physics
applied to an astrophysical problem).

<quote>
Dark matter halos grow by merging. This merging requires them to be attractive, but the simplest manifestation of monopole dark matter is repulsive.
<end quote>

!!!

Don't let this throw you off.

Unfortunately these monopoles repel and so the charge Q > 1 halos are unstable. This may rule out our model. Then again, protons repel but
visible matter is mostly made of protons, as the repulsion at small
distances is canceled by neutrons and at large distances is screened by electrons. The monopoles only repel at long distances. So what are the analogs of the electrons? Electrons carry the opposite charge from
protons but cannot annihilate with protons as they carry a flavor
quantum number and the lightest state for a decay product, the neutron,
is too massive for the decay to be kinematically allowed. Similarly such=

a flavor quantum number for the monopoles is an automatic consequence of=

our fermionic couplings. The masses of the various flavors of monopoles
can be adjusted by choosing the Yukawa couplings. We propose to include
light antimonopoles of a different flavor which screen the long distance=

repulsion of our monopoles. If such a screening cannot be made to work,
our proposal will be excluded.
<end quote>

Let's see then...

They have to first find out the "electrons" that would screen out the repulsion between those galaxy sized monopoles.

All this is interesting, yes, but it is very difficult to gauge if there=

is any connection with reality at this stage. Mathematics is an infinite=

forest, and it is very easy to lose your way in the equation undergrowth.=

..

Obviously too, I am in NO WAY able to follow precisely those papers, and=

can only look at the conclusions.

The thing which makes this idea interesting is that it explains, at one
fell swoop, many of the most pressing problems at the border between
cosmology and astrophysics, in particular the observed properties of
low-mass galaxies, satellite galaxies, the matter distribution within
galaxies, and so on. Yes, the theory itself is one of many, but this it
has in common with other candidates. What makes it interesting is that
it explains much more and makes robust testable predictions.

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