Physicist suggests new experiments could make or break axion as dark matter theory

January 26, 2015 by Bob Yirka report
A massive cluster of yellowish galaxies, seemingly caught in a red and blue spider web of eerily distorted background galaxies, makes for a spellbinding picture from the new Advanced Camera for Surveys aboard NASA's Hubble Space Telescope. To make this unprecedented image of the cosmos, Hubble peered straight through the center of one of the most massive galaxy clusters known, called Abell 1689. The gravity of the cluster's trillion stars — plus dark matter — acts as a 2-million-light-year-wide lens in space. This gravitational lens bends and magnifies the light of the galaxies located far behind it. Some of the faintest objects in the picture are probably over 13 billion light-years away (redshift value 6). Strong gravitational lensing as observed by the Hubble Space Telescope in Abell 1689 indicates the presence of dark matter. Credit: NASA, N. Benitez (JHU), T. Broadhurst (Racah Institute of Physics/The Hebrew University), H. Ford (JHU), M. Clampin (STScI),G. Hartig (STScI), G. Illingworth (UCO/Lick Observatory), the ACS Science Team and ESA

(—Leslie Rosenberg, a physicist with the University of Washington has published a paper in Proceedings of the National Academy of Sciences, describing the current state of research that involves investigating the possibility that axions are what make up dark matter. He also offers some perspective on the work suggesting that at least one project is likely to lead to either proving or disproving that axions are dark matter.

For several years now, scientists have been hard at work trying to detect WIMPs, the thinking has been that if they can be detected, then it would go a long way towards proving that they are what makes up dark matter—the theoretical stuff that is now believed to make up approximately 85 percent of all mass in the universe. Unfortunately, despite their best efforts, scientists have not yet been able to detect the presence of a single one, causing some to wonder if they exist at all. That doubt has led some scientists to consider other types of particles as dark matter candidates—one of them is the neutrino, though more and more it appears to be falling from favor. Another is the axion, a particle first theorized in the early 70's. One of its major proponents is Rosenburg, who has been developing experimental devices with the purpose of either proving that dark matter is made up of axions, or it is not.

Axion theory suggests that axions can decay into photons—one axion into two photons, and vice-versa—the inbetween state is known as the virtual axion. Because of this property, most axion detectors are dedicated to measuring them after they have decayed into photons because that is something we know how to detect. Rosenburg describes research into devices meant to study the impact axions may have on the sun, or halos around astronomical objects, and notes that super novae should also produce them. He also notes that some experiments are looking into what has come to be known as "Shining light through walls"—the idea being if axions decay into photons just after passing through a wall, or other object, it should be possible to detect them. The problem here of course would be proving that they have anything to do with dark matter.

Rosenburg then describes a radio frequency approach, another way to capture axions decaying into light—current experiments in this area are meant to capture axions that are part of the Milky Way's dark matter halo. In this case, the idea is to rouse the axions into decaying into and then detecting them—the most prominent project appears to be the Axion Dark Matter eXperiment (ADMX), which Rosenburg claims is likely to either prove or disprove axions as once and for all.

Explore further: Mathematical scientist suggests possible test for existence of axions

More information: Dark-matter QCD-axion searches, Leslie J Rosenberg, PNAS, DOI: 10.1073/pnas.1308788112

In the late 20th century, cosmology became a precision science. Now, at the beginning of the next century, the parameters describing how our universe evolved from the Big Bang are generally known to a few percent. One key parameter is the total mass density of the universe. Normal matter constitutes only a small fraction of the total mass density. Observations suggest this additional mass, the dark matter, is cold (that is, moving nonrelativistically in the early universe) and interacts feebly if at all with normal matter and radiation. There's no known such elementary particle, so the strong presumption is the dark matter consists of particle relics of a new kind left over from the Big Bang. One of the most important questions in science is the nature of this dark matter. One attractive particle dark-matter candidate is the axion. The axion is a hypothetical elementary particle arising in a simple and elegant extension to the standard model of particle physics that nulls otherwise observable CP-violating effects (where CP is the product of charge reversal C and parity inversion P) in quantum chromo dynamics (QCD). A light axion of mass 10−(6–3) eV (the invisible axion) would couple extraordinarily weakly to normal matter and radiation and would therefore be extremely difficult to detect in the laboratory. However, such an axion is a compelling dark-matter candidate and is therefore a target of a number of searches. Compared with other particle dark-matter candidates, the plausible range of axion dark-matter couplings and masses is narrowly constrained. This focused search range allows for definitive searches, where a nonobservation would seriously impugn the dark-matter QCD-axion hypothesis. Axion searches use a wide range of technologies, and the experiment sensitivities are now reaching likely dark-matter axion couplings and masses. This article is a selective overview of the current generation of sensitive axion searches. Not all techniques and experiments are discussed, but I hope to give a sense of the current experimental landscape of the search for dark-matter axions.

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1 / 5 (4) Jan 26, 2015
Why? Why create a mystery to solve a mystery? Maybe the problem is our approach!
Jan 26, 2015
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Jan 26, 2015
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1.3 / 5 (4) Jan 26, 2015
Or perhaps DM is just the superposition of the gravitational curvatures of the all the matter in the clusters. Ie. the halfway point on a radial line between two galaxies instead of being zero gravity is just a point where the pull toward either galaxy is the same. The point itself may have a gravitational pull of its own when viewed from far enough away, perpendicular to that point. Not because there is a mass there, but because space at that point is curved.
Jan 26, 2015
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Jan 26, 2015
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Jan 26, 2015
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2.3 / 5 (3) Jan 27, 2015
There is evidence of dark matter every time a double slit experiment is performed; it's what waves.

Dark matter has mass. Dark matter physically occupies three dimensional space. Dark matter is physically displaced by the particles of matter which exist in it and move through it.

The Milky Way's halo is not a clump of dark matter anchored to the Milky Way. The Milky Way is moving through and displacing the dark matter.

The Milky Way's halo is the state of displacement of the dark matter.

The Milky Way's halo is the deformation of spacetime.

What is referred to geometrically as the deformation of spacetime physically exists in nature as the state of displacement of the dark matter.

A moving particle has an associated dark matter displacement wave. In a double slit experiment the particle travels through a single slit and the associated wave in the dark matter passes through both.
1 / 5 (4) Jan 27, 2015
Dark matter has electromagnetic properties and exists everywhere. They keep looking for particles that do not exist.
5 / 5 (4) Jan 27, 2015
This seems to be a crazy idea which postulates one LESS mysterious hypothetical particle - dark-matter that arising from another MORE mysterious hypothetical particle -axion. Actually the recent thing what which we have found in the standard model of particle physics –the Higgs field (which is the source of the Higgs particle) is more likely to be the searching dark-matter
No, it postulates one possible particle--the axion, as a (complete or partial) possible explanation to the undefined place holder--dark matter.
Why do you feel the compulsive need to continually spam your vacuum mechanics site? Have you ever made a post without doing so? You're like the Jehovah's Witnesses of science sites.
5 / 5 (3) Jan 27, 2015
IronhorseA: "the halfway point on a radial line between two galaxies instead of being zero gravity is just a point where the pull toward either galaxy is the same." How would that maintain cohesiveness *within* a galaxy, so that it doesn't spin apart?
Losix: "The dark matter particles are detectable easily, they can be also prepared in the lab"
Swordsman: "Dark matter has electromagnetic properties and exists everywhere." If they have electromagnetic properties, are easily detected, why is it then that virtually everything I read about DM describes the inability of science to detect it, except here in the comments sections of articles like this?
Jan 27, 2015
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not rated yet Jan 27, 2015
I hadn't read much about the Axion in the past so this article prompted me to look up other articles on it. I'm certainly not knowdgable enough about particle physics to understand anything in detail but from what I've now read it seems that the Axion would solve a lot of problems and I don't mean "just" the dark matter problem. It wasn't even postulated to solve that problem, it was postulated to solve an issue in QCD. So you have a particle that's theorized to solve one problem and it actually solves the dark matter problem as well. Additionally, the solar coronal heating problem and the seasonal variation in x-rays observed in the atmosphere.

It sounds like the axion may be the winner.

This article by a scientist studying WIMP's was extremely insightful.

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