The whole question of how one arrives at hypotheses about DM particle is interesting. I see that
axion dark matter is technically different from
weakly interacting (WIMP) dark matter.
==quote==
Weakly interacting massive particles
From Wikipedia, the free encyclopedia
(Redirected from
Weakly Interacting Massive Particle)
In
particle physics and
astrophysics,
weakly interacting massive particles, or
WIMPs, are among the leading hypothetical particle physics candidates for
dark matter. The term “WIMP” is given to a dark matter particle that was produced by falling out of
thermal equilibrium with the hot dense
plasma of the early universe, although it is often used to refer to any dark matter candidate that interacts with standard particles via a force similar in strength to the
weak nuclear force. Its name comes from the fact that obtaining the correct abundance of dark matter today via thermal production requires a self-
annihilation cross section of [PLAIN]https://upload.wikimedia.org/math/1/2/7/127a07aed49edf56b91a9709ae732625.png, which is roughly what is expected for a new particle in the 100
GeV mass range that interacts via the
electroweak force. This apparent coincidence is known as the “WIMP miracle”. Because
supersymmetric extensions of the
standard model of particle physics readily predict a new particle with these properties, a stable supersymmetric partner has long been a prime WIMP candidate.
[1] However, recent null results...
==endquote==
It puzzles me that axions are said to interact primarily via GRAVITY AND EM, not via the strong or weak forces! They are even predicted to convert back and forth to PHOTONS in a strong magnetic field, and that has become a way to search for them, using strong magnetic fields!
So this is very curious--a proposed DM particle that is not a WIMP.
==quote==
Axion
From Wikipedia, the free encyclopedia
Interactions Gravity,
electromagnetic
Status Hypothetical
Symbol A0
Theorized 1977,
Peccei and
Quinn
Mass 10−6 to 1
eV/
c2
Electric charge 0
Spin 0
The
axion is a hypothetical
elementary particle postulated by the
Peccei–Quinn theoryin 1977 to resolve the
strong CP problem in
quantum chromodynamics (QCD). If axions exist and have low mass within a specific range, they are of interest as
a possible component of
cold dark matter.
...
...
The critical mass is of order 10−11 times the electron mass, where axions may account for the dark matter. The axion is thus a dark matter candidate as well as a solution to the strong CP problem. Furthermore, in 1983, Pierre Sikivie wrote down the modification of Maxwell's equations from a light stable axion
[8] and showed axions can be detected on Earth by converting them to photons with a strong magnetic field, the principle of the
ADMX. Solar axions may be converted to x-rays, as in
CAST. Many experiments are searching laser light for signs of axions.
[9]
Experiments
The Italian
PVLAS experiment searches for polarization changes of
light propagating in a magnetic field. The concept was first put forward in 1986 by
Luciano Maiani, https://en.wikipedia.org/w/index.php?title=Roberto_Petronzio&action=edit&redlink=1 and
Emilio Zavattini.
[10] A rotation claim
[11] in 2006 was excluded by an upgraded setup.
[12] An optimized search began in 2014.
Another technique is so called "light shining through walls",
[13] where light passes through an intense magnetic field to convert photons into axions, that pass through metal...
Several experiments search for astrophysical axions by the
Primakoff effect, which converts axions to photons and vice versa in electromagnetic fields. Axions can be produced in the Sun's core when x-rays scatter in strong electric fields. ...
...
Possible detection
Axions may have been detected through irregularities in X-ray emission due to interaction of the Earth's magnetic field with radiation streaming from the Sun. Studying 15 years of data by the
European Space Agency's
XMM-Newton observatory, a research group at
Leicester University noticed a seasonal variation for which no conventional explanation could be found. One potential explanation for the variation, described as "plausible" by the senior author of the paper, was X-rays produced by axions from the Sun's core.
[29]
...
Properties
Predictions
One theory of axions relevant to
cosmology had predicted that they would have no
electric charge, a very small
mass in the range from 10−6 to 1 eV/
c2, and very low interaction
cross-sections for
strong and
weak forces. Because of their properties, axions would interact only minimally with ordinary matter. Axions would change to and from
photons in magnetic fields.
Cosmological implications
Theory suggests that axions were created abundantly during the
Big Bang.
[36] Because of a unique coupling to the
instanton field of the primordial
universe (the "
misalignment mechanism"), an effective
dynamical friction is created during the acquisition of mass following
cosmic inflation. This robs all such primordial axions of their kinetic energy.
If axions have low mass, thus preventing other decay modes, theories predict that the universe would be filled with a very cold
Bose–Einstein condensate of primordial axions. Hence, axions could plausibly explain the
dark matter problem of
physical cosmology.
[37] Observational studies are underway, but they are not yet sufficiently sensitive to probe the mass regions if they are the solution to the dark matter problem. High mass axions of the kind searched for by Jain and Singh (2007)
[38] would not persist in the modern universe. Moreover, if axions exist, scatterings with other particles in the thermal bath of the early universe unavoidably produce a population of hot axions.
[39]
Low mass axions could have additional structure at the galactic scale. As they continuously fell into a galaxy from the intergalactic medium, they would be denser in "
caustic" rings, just as the stream of water in a continuously-flowing fountain is thicker at its peak.
[40] The gravitational effects of these rings on galactic structure and rotation might then be observable.
[41] Other cold dark matter theoretical candidates, such as WIMPs and
MACHOs,...
Axions would also have stopped interaction with normal matter at a different moment than other more massive dark particles. The lingering effects of this difference could perhaps be calculated and observed astronomically. ...
===endquote===
So it seems that hypothetical axions are being considered for DM and that they are not the same as wimps, and they don't even interact significantly via the weak force!
