Signs of dark matter may point to mirror matter candidate

( -- Dark matter, which contains the "missing mass" that's needed to explain why galaxies stay together, could take any number of forms. The main possible candidates include MACHOS and WIMPS, but there is no shortage of proposals. Rather, the biggest challenge is finding some evidence that would support one or more of these candidates. Currently, more than 30 experiments are underway trying to detect a sign of dark matter. So far, only two experiments claim to have found signals, with the most recent observations coming just a month ago. Now, physicist Robert Foot from the University of Melbourne has shown that the results of these two experiments can be simultaneously explained by an intriguing dark matter candidate called mirror matter.

As it name implies, mirror matter is basically a spatial reflection of . can be either left-handed or right-handed, so if an ordinary matter particle were left-handed, its mirror particle would be right-handed, but exactly identical in every other way. In the theory of mirror matter, every ordinary matter particle (e.g. protons, electrons, etc.) would have a mirror particle, thus doubling the number of particles in the universe.

The inspiration for mirror matter came from an experiment performed in 1956 that showed that the laws of nature are not left-right symmetrical (also called parity-symmetrical, or p-symmetrical). Specifically, the experiment showed that particles in weak interactions display a preference for left-handedness, so that in a way, the Universe is left-handed. Since the other two forms of - rotational and translational - do seem to be symmetrical everywhere in nature, scientists wonder why nature doesn’t have p-symmetry as well. But if mirror matter exists, it would solve this problem by having slight right-handedness and restoring the Universe’s p-symmetry.

At first, mirror matter may sound a bit like (which is ordinary matter with an opposite charge). In both theories, the number of known particles would double. However, while antimatter interacts very strongly with ordinary matter, annihilating itself into photons, mirror matter would interact very weakly with ordinary matter. For this reason, some physicists have speculated that mirror particles could be candidates for dark matter. Even though mirror matter would produce light, we would not see it, and it would be very difficult to detect.

However, mirror matter would not be impossible to detect, and Foot thinks that the DAMA experiment and the CoGeNT experiment may have detected mirror matter. In DAMA, scientists observed a piece of sodium iodide, which should generate a photon when struck by a dark matter particle. Since the experiment is Earth-based, the scientists predicted that they would observe more photons during the time of year that the Earth is moving toward the dark matter background than away from it - and they did. The more recent CoGeNT experiment is similar, where scientists found evidence of dark matter collisions in a germanium crystal. Interestingly, both DAMA’s and CoGeNT’s results involve particles of a similar mass range.

In Foot’s model, if ordinary and mirror particles interact with each other via a process called photon-mirror photon kinetic mixing, then mirror particles could explain both results. In Foot’s theory, a mirror particle plasma would be the predominant ingredient in galactic halos, where dark matter seems to be “hiding” based on observations of its gravity’s effects. While this proposal supports the possibility of mirror matter as , Foot added that experiments in the near future will further test this idea.

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Exploring the secrets of dark matter

More information: Robert Foot. "A CoGeNT confirmation of the DAMA signal." arXiv:1004.1424v1 [hep-ph]
via: Technology Review

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Apr 27, 2010
What does changing the left/right handedness of a substance have to do with its ability to be detected?

Apr 27, 2010
Could these mirror particles be the discarded (by the Copenhagen gang) negative energy portion of the Dirac equation, i.e. binding energy? And/or an aether composed of electrons and positrons from which the "virtual particles" arise?

Apr 27, 2010
did anyone catch whether we are talking about chirality or helicity. Helicity being the particles spin is in the same direction as its momentum and chirality I still don;t really understand. -- which one for mirror particles??

Apr 27, 2010
Aether is not composed of electrons and positrons. Such theory is much more close to Plasma cosmology, attributed to Nobel Prize winner Hannes Alfvén.


Mirror matter concept is identical to antimatter, in fact. The phrase "mirror matter" was introduced by Bob L. Forward as an alternative term for what is commonly called antimatter, in an attempt to emphasize that antimatter is identical to ordinary matter, except reversed in all possible ways.


This article would contradict the previous article, in which antimatter isn't linked to dark matter.


"Signs of dark matter may point to antimatter candidate" versus "Astrophysicists cast doubt on link between excess positrons and dark matter"

As you can see, in today's physics is possible to tell whatever you want, if you change terminology a bit.

Apr 27, 2010
Sigh! Mirror matter is not antimatter. Yes, Forward suggested the term for anti-matter, but then it turned out that anti-matter preserves p-handedness.

It is easier to understand looking at photons. Photons have spin, it is about the only intrinsic property that they do have. When matter and anti-matter annihilate, they produce photons with normal spin. Mirror photons (if they exist) have opposite spin and normally won't interact with non-mirror matter.

The other thing to understand about mirror matter is that it does not need to have identical (except spin reversed) characteristics. The best example I can use is deuterium. Normal deuterium has spin 1, the neutron and proton spins aligned. If you flip the spin of one or the other, the spin zero deuteron falls apart. If mirror matter exists in large quantities, any particles with no handedness would be identical to normal matter. As a result there should be no baryonic mirror matter to clump into stars and galaxies.

Apr 27, 2010
I'm sorry, this article was very confusing. Are you talking about SUSY and spin when you refer to "mirror matter" and "left/right hand?"

Apr 27, 2010
"did anyone catch whether we are talking about chirality or helicity."

Since we are talking about p-parity (i.e. 'normal' matter and antimatter being left handed while mirror matter and mirror-antimatter would be right handed) I think we're talking about chirality here.


"What does changing the left/right handedness of a substance have to do with its ability to be detected?"

Maybe the particular property needs to be in sync for interactions to take place (e.g.there must be some 'conservation of parity' between interacting particles). Just like photons may only be caught by atoms if the energy fits a discrete set of energies one might speculate that the parities must 'fit' for two pieces of matter to interact.

I'm thinking of something akin to the 'Star Trek' notion of 'frequencies' that must be in tune for stuff to affect each other.

Apr 27, 2010
Isn't there supposed to be a whole lot more dark matter than ordinary matter? If this mirror matter is supposed to balance out the left handedness of the universe, then that much mirror matter would make the problem even worse in the other direction.

Apr 27, 2010
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Apr 27, 2010
The question is, what the "mirror matter" is supposed to balance?

The total mass of the universe. One thousand characters is not enough to even start to describe the astronomical evidence that dark matter exists, and due to gravitational lensing, we know how dark matter is distributed in certain galaxy clusters.

Why can't dark matter be some form of normal matter? Again not enough space. The two closest possibilities are thermal (low-energy) neutrinos and mini (sub-stellar mass) black holes. The neutrino model fails because they would have left a signature in the cosmic backgroud radiation. The possibility of clouds of mini-black holes is eliminated by looking for weak lensing.

Could some of the missing mass be small black holes and/or neutrinos? Sure, but not nearly enough. This is what started the search for possible particles with little or no interaction with light. Yes, lots of candidates have been proposed--but many have already been ruled out.

Apr 27, 2010
So I wonder what new entity is going to be used to explain Mirror matter.

If there is a sidereal periodicity to the mirror matter signal then they are detecting the Aether.

Apr 28, 2010
From my admittedly limited understanding of mirror matter, it makes sense. If all the normal matter we see spins one way, particles spinning the opposite way would balance out the equation. What's more, we would no longer need an explanation for a left handed universe if mirror matter balaced things out to a no-handed universe. What I don't understand is why mirror matter would be dark.

Apr 28, 2010
What I don't understand is why mirror matter would be dark.

Conservation laws. I'm not even going to try to draw Feynman diagrams here, so bear with me. Take a simple case of a three particle interaction, say a positron and an electron coming together to create a photon. Two spin 1/2 particles creating a spin 1 particle. (You can reflect or rotate this diagram and it still makes sense, one of the wonderful things about Feynman diagrams.)

Now start with a spin -1 mirror photon and a normal electron. If they react, you get a -1/2 spin (i.e. mirror particle) with a charge of -1. If that (hypothetical) mirror particle has a large mass, the reaction will be energetically unfavorable. What if we start with a proton or a neutron? The mirror particle now needs to conserve baryon number.

If someone can come up with a neat model with masses that all work so that mirror photons don't normally interact with normal matter, they get a Nobel--if and when someone verifies it.

Apr 28, 2010
If you want to start on your Nobel prize, you will also need to fit within the parameters of current big bang models, and you probably also need mirror matter particles that don't clump. This is why neutrinos are such a tempting candidate for dark matter--they work almost perfectly. No charges so no charged clouds of dark matter, they don't form atoms, or stars or any other sort of clumps, and they react incredibly infrequently with normal matter.

Hmmm. What if neutrinos have a high enough cross section with each other, and those collisions can release negative spin photons that react only with neutrinos. Check back with me in a year or six... (The place to look for evidence would be in core collapse supernovas. Such a theory would result in slightly faster energy loss in neutrinos.)

Apr 28, 2010
Oops, or maybe not so oops. This gets strange quick. The problem is that we need something that gravitationally clumps, and the mirror photons wouldn't do that. However, not all dark matter has to clump, in fact I think gravitational lensing, etc. can account for only about as much mass as normal matter. (Have to check that...)

But what if neutrinos are tachyons? The hot gas of neutrinos in the big bang would emit energy in mirror photons, and speed up. (As tachyons speed up they lose mass.) So we have this sea of very low energy neutrinos moving very fast. Along comes a core collapse supernova and creates a road-block of very high-energy (low speed, just a bit faster than light) neutrinos that interact with the very low energy neutrinos that come flying in. The math is simple. The number of very low energy neutrinos trapped would be literally astronomical. The result would be a cloud of (light speed) mirror photons leaving the galaxy core at the speed of light.

Apr 29, 2010
Are tachyons with non-zero spin possible?

In theory? Sure. Electric charge, even non-zero distribution of charge as in neutrons? No. Incidentally there are several observations of neutrino speeds which indicate they are tacyons, although the observed excess speed is very small, and consistent with a speed of c. The problem is that these measurements are not really consistent with a speed below c, and you can't have neutrino oscillations at c. See the MINOS results and the detection of neutrinos from supernova 1987a for more information.

Also, a lot of work has been done on "sterile" neutrinos as cold or warm dark matter. This is usually conceived of as a fourth neutrino flavor, but with reversed chirality from the three known neutrinos. Antineutrinos have reversed (right) chirality relative to neutrinos, so presumably sterile antineutrinos would have left chirality.

Apr 29, 2010
Isn't there supposed to be a whole lot more dark matter than ordinary matter? If this mirror matter is supposed to balance out the left handedness of the universe, then that much mirror matter would make the problem even worse in the other direction.

The mirror matter would be (part of) the "dark matter" we are missing. It behaves just like the dark matter we are (not) seeing: i.e. it does not interact with our 'left handed' matter or our 'left handed' photons. But it does have gravitational effects (since left handed and right handed gravitons are identical)

Apr 29, 2010
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May 03, 2010
Is it possible that "dark matter" is simply composed of boson strings?

May 05, 2010
Dark matter, Dark energy, now mirror matter - where's it all going to end?
My head is spinning already - I think I'm in need of some solid light energy.

Jokes aside; I just want to know if the "dark" energy [and hence dark matter] we're looking for cannot be found in a universe that has a polar axis around which all galaxies are rotating?

This would give a perfectly good old mechanistic explanation for all the missing energy we're looking for: easy enough to calculate the angular momentum/velocity/acceleration of galaxies around a polar axis. It would also give a very good explanation for why galaxies are not just flying apart from each other.

Just a thought. Shoot it down in flames if you wish. But first please do consider all the astronomical evidence already gathered so far.

May 07, 2010
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May 07, 2010
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May 07, 2010
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