Part 1 – Is Dark Matter the “Heavy Shadow” of Visible Matter?

Graphic depicting visible matter worlds above the blue rectangle and bigger, heavier "shadow," or partner, particles below the blue rectangle that are not seen in the visible matter worlds. Supersymmetry theory in physics postulates that every particle we observe has a massive "shadow-partner" particle. No supersymmetric particle has yet been seen. Image courtesy CERN, Switzerland.
Graphic depicting visible matter worlds above the blue rectangle and bigger, heavier “shadow,” or partner, particles below the blue rectangle that are not seen in the visible matter worlds. Supersymmetry theory in physics postulates that every particle we observe has a massive “shadow-partner” particle. No supersymmetric particle has yet been seen. Image courtesy CERN, Switzerland.

January 13, 2004  Ann Arbor, Michigan – In February 2001, the Brookhaven National Laboratory in Upton, Long Island, New York, announced that physicists there had made a new measurement of what is called, “the muon anomalous magnetic moment.” The number looks like this:

From "Theory of the Muon Anomalous Magnetic Moment" by Andrzej Czarnecki, September 2002 Seventh International Workshop on Tau Lepton Physics, Santa Cruz, California.
From “Theory of the Muon Anomalous Magnetic Moment” by Andrzej Czarnecki, September 2002 Seventh International Workshop on Tau Lepton Physics, Santa Cruz, California.

The problem was that this more refined calculation exceeded the theoretical prediction of what the muon’s magnetic attraction should be by about 2.6 standard deviations. Or more simply, if the Standard Model (see More Information below) of atomic physics is correct, the muon’s anomalous magnetic moment should be a different number.

Since 2001, theoretical physicists have argued about whether the Brookhaven muon measurement is correct or not. If it is, then Something Else in the universe is not being counted in the calculations. Some physicists such as Gordon Kane, Ph.D., Theoretical Particle Physicist and Particle Cosmologist at the University of Michigan’s Randall Physics Laboratory in Ann Arbor, argue that the Something Else is Dark Matter, the “shadow universe” that does not give off light, remains invisible to our eyes, but can be detected by instruments that can measure magnetic strengths of atomic particles down to an accuracy of one part in 100 billion.

Dark Matter, he thinks, is an intimate and more massive partner with our visible matter universe, made of heavy particles that are unstable and decay into other particles. The Dark Matter “super partner particles” could be five to ten times more massive than our visible matter protons. If this hypothesis is true, that “heavier shadow” would make up more of the universe. That might explain why 23% of the universe is unseen Dark Matter, 73% is mysterious Dark Energy and only 4% is visible matter.

Dark Matter Distribution in the Universe

An international team of astronomers based in France has obtained the first-ever glimpse of the distribution of dark matter over a large section of sky. The team used images from the Canada-France-Hawaii Telescope’s high-resolution wide-field imaging camera to analyze the light of 200,000 distant galaxies, looking for distortions caused by intervening dark matter. The results give cosmologists their first clear window into the possible roles of dark matter in the evolution of the Universe.

Deflection of light rays crossing the universe, emitted by distant galaxies. The box shown spans a distance of about one billion light-years. The structures are displayed so that the brighter regions have a higher density (that is, more dark matter) than the darker regions. The dark matter is concentrated into a web-like distribution of filaments that intersect at dense nodes where great clusters of galaxies are expected to form and become visible. This numerical simulation was made available by S. Colombi of the IAP.
Deflection of light rays crossing the universe, emitted by distant galaxies. The box shown spans a distance of about one billion light-years. The structures are displayed so that the brighter regions have a higher density (that is, more dark matter) than the darker regions. The dark matter is concentrated into a web-like distribution of filaments that intersect at dense nodes where great clusters of galaxies are expected to form and become visible. This numerical simulation was made available by S. Colombi of the IAP.

At the rear of the cube (to the left), three blue disks represent three distant galaxies. The yellow lines that cross the box represent light rays from those galaxies propagating through the universe. In the absence of intervening matter, the light would travel on straight lines but in the presence of matter, the paths of the rays are evidently deflected by the gravitational effects of the clumpy matter (the breaks in the yellow lines illustrate the light passing behind a clump of dark matter).

The light from a distant galaxy rarely encounters a clump of mass to strongly bend the light and cause an easily seen distortion. Instead the individual light rays suffer a series of small deflections such that an observer located at the front of the box (to the right), sees that the images of all the galaxies in some small patch of the sky, near to one of our test galaxies say, are all very slightly elongated in a common direction determined by the distribution of dark matter along that particular line of sight. This gravitational distortion is expected to be very small and requires a careful statistical treatment on many patches over the sky.

This view shows what the observer at the front of the box would perceive when looking at galaxies in the sky. The blue elongated disks are the images of distant galaxies formed by their light after it has passed through the box.This numerical simulation was kindly made available by S. Colombi of the IAP.
This view shows what the observer at the front of the box would perceive when looking at galaxies in the sky. The blue elongated disks are the images of distant galaxies formed by their light after it has passed through the box.This numerical simulation was kindly made available by S. Colombi of the IAP.

The observer can see these galaxies but the filaments of dark matter, shown here in red and white, are invisible, even to the largest telescopes available to our observer. However, one can see that the galaxy images are elongated in a special way on average: they are stretched along a direction parallel to the filaments of dark matter. This effect is a consequence of gravitational lensing which stretches the tight bundle of light rays from a single galaxy much like the moon’s gravity stretches the Earth to cause the ocean tides. By measuring the systematic distortion in the images of distant galaxies, one can “see” the dark matter. The ultimate goal of the French team is to map the dark matter with the new CFHT instrument MegaCam, as one of the special survey programs now being planned.


Interview:

Gordon Kane, Ph.D., Theoretical Particle Physicist and Particle Cosmologist at the University of Michigan’s Randall Physics Laboratory in Ann Arbor, Michigan: “What the experimenters find is what they observe is a little bit stronger magnet (in the muon) than what the prediction says. So, it is a signal that there is an affect of some physics that is not included in the Standard Model.

THAT COULD BE CAUSED BY THE SHADOW UNIVERSE?

Shadow universe, yes, of dark matter. So the connection is the following – it’s been known for some time that an extension of the Standard Model called ‘Supersymmetry’ does affect the magnetic strength of subatomic particles.

If Supersymmetry is right as a description of Nature, then another set of particles does have to exist like the particles we know such as electrons, and muons and photons and gluons that hold together quarks, and protons. There has to be a whole other set of particles. Each of the particles we know has to have a partner. Historically, that’s not such an odd thing. For example, Dirac 70 some years ago predicted that every particle had an anti-particle and that came out to be true, even though at the time it was thought to be a far out idea. This is in some ways a similar idea: every particle has a partner and what we’re seeing is the affect of these partners on the magnetic strength.

 

The Shadow Universe of Dark Matter

In Supersymmetry, the expected ‘super partners’ (to all known subatomic particles) would exist and most of them would be heavy particles and are unstable and decay into other particles. A few are stable. But the lightest of the new ‘super partner’ particles – we don’t know exactly its nature yet ­ but it’s called the ‘lightest super partner’ in the literature. That lightest super partner should be a stable particle which was created at the Big Bang, just like all the other particles were created at the Big Bang and have persisted in the universe until now.

The electrons and quarks in us were also created at the Big Bang. All the particles that make us up are ones left over from the Big Bang and this new set of particles, the lightest super partner, would be added to the set that are already around. It has, in fact, just the right properties to make up what is called the ‘dark matter’ that makes up 23% of the universe. It is called ‘dark’ because you don’t actually see it in the sense that we see planets and stars. But instead, you infer its existence because of its gravitational impact on other things. So, it makes the motion of planets and galaxies or solar systems and galaxies different from what they would be otherwise. You can measure that and you can infer there must be some matter there, but you don’t see it with light. You see it instead by its gravitational affects.

Visible universe of galaxies, stars and planets makes up only 4% of the known universe. Dark Matter that is invisible makes up 23% of the universe. Images courtesy Center for Particle Astrophysics, University of California-Berkeley.
Visible universe of galaxies, stars and planets makes up only 4% of the known universe. Dark Matter that is invisible makes up 23% of the universe. Images courtesy Center for Particle Astrophysics, University of California-Berkeley.


Only 4% of Universe Is Made of Visible Particles

Suppose the 4% is made up of a bunch of particles, namely protons and neutrons and electrons. They have some weight, those particles. OK? Then suppose there are the same number of particles in Dark Matter as those approximately. So, that would be the most naive assumption you could make ­ that since they are super partners, for every regular particle, there is a Dark Matter particle crudely speaking. Then if the Dark Matter particles tended to have 5 to 10 times the mass of the proton, instead of 4%, they would be 40%.

SO, THE SHADOW UNIVERSE WOULD BE DENSER OR HEAVIER?

The particles in it are just heavier by 5 to 10 times and some of those super partners are the ones that are thought to explain this extra magnetic strength in the muons that indicates something else is going on. So that is the chain of reasoning.

THE IMPLICATION IS THAT THE DARK MATTER MYSTERY COULD BE EXPLAINED AS HEAVIER PARTNERS TO EVERY PARTICLE THAT WE KNOW IN THE UNIVERSE?

That’s right. It’s just that we haven’t had enough energy and machines yet to make them. But, right now the Tevatron Collider is looking for the hypothesized heavy particles at the Fermi Lab outside Chicago. And around 2007 to 2008, the large collider being built at CERN in Geneva, Switzerland, will be turned on. Those machines do have the energy to make these super particles. The Tevatron has the energy to make them, but might make too few of them to detect. The large collider at CERN might make many of them because it’s much more intense. So, then we should see this world of super partners completely explicitly, just as much as we see top quarks and double bosons and such things. They should no longer be hidden from us at that point. They will be completely explicit and we’ll have lots of fun talking about them. But all of them are unstable. They have lifetimes that are only a tiny fraction of a second, except the lightest one. And that’s the one that hangs around in the universe forever, or almost forever.

Finally, the implication is that there is a new physics beyond the Standard Model and that the best candidate to explain everything is the Supersymmetry idea.”


More Information:

Standard Model Theory of Atomic Physics:

Attempts to describe all matter and forces in the universe (except gravity). Its explains hundreds of particles and complex interactions in terms of a few fundamental particles and interactions. There are
particles that carry forces such as photons and
particles that are matter such as electrons, protons, neutrons, and quarks.

­ Force Carrier Particles: Each type of fundamental force is “carried”
by a force-carrier particle such as a photon.

­ Matter Particles: The Standard Model says that most matter particles we know
are composites of more fundamental particles called “quarks.” The second fundamental
group of matter particles are called leptons. Electrons are leptons.

 

Continued in Part 2.


Website:

http://pdg.web.cern.ch/pdg/cpep/adventure_home.html

 


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