Celestia Forums

Hmm... I'm posting this here because of certain political issues with the Physics and Astronomy forum (which have been discussed elsewhere).

What is the current view on "mirror matter" - I seem to recall a while back there was a bit of a fuss in the media about it being a possible candidate to explain dark matter, close-in extrasolar giant planets, Nemesis, the apparent lack of dead comets and craters on small solar system bodies. Haven't heard much about it recently - is it still an active area of research (and was it ever?), or has the notion been discarded?

chaos syndrome wrote:Hmm... I'm posting this here because of certain political issues with the Physics and Astronomy forum (which have been discussed elsewhere).

What is the current view on "mirror matter" - I seem to recall a while back there was a bit of a fuss in the media about it being a possible candidate to explain dark matter, close-in extrasolar giant planets, Nemesis, the apparent lack of dead comets and craters on small solar system bodies. Haven't heard much about it recently - is it still an active area of research (and was it ever?), or has the notion been discarded?

Hi Chaos,

presumably tonight, I'll find some time to write a brief summary about the status of Mirror Matter (MM) both from the particle physics and astrophysics perspective. While for astrophysicists MM may appear as an elegant possible candidate for Dark Matter, offering a solution for certain associated puzzles, it is not popular at all among particle physicists. I'll try to make clear why.

Meanwhile, I'll refer you to a respective paper by one of the fathers of the Standard Model of elementary particles, who is "crowned" by the Nobel price:

Positronium versus the mirror universe

S. L. Glashow a, b, 1

a Lyman Laboratory of Physics, Harvard University, Cambridge, MA 02138, USA
b Department of Physics, Boston University, Boston, MA 02215, USA

Received 15 November 1985. Available online 10 October 2002.


Abstract

A mirror universe of fermions and forces isomorphic to but distinct from those we see couples directly to our universe only by gravity. Particles at any mass scale enjoying both normal and shadow forces forge an electromagnetic link (by radiative corrections) between the two universes such that mirror particles display conventional electric charges 10??’3?€“10??’5 e. This produces mixing between triplet positronium and its analogous mirror state through a one-photon annihilation diagram. Consequent effects are contrary to experiment. The possible existence of such a mirror universe is thereby excluded.

Cheers,
Fridger

Chaos,

perhaps -- before I write a more detailed respective explanation -- it would be useful to let me know whether you are satisfied with my above "telegram-style" answer already or whether you'd really like to know things in more detail. No problem if you do, but it saves me work if you don't

Bye Fridger

Thanks for the info - my Google searching had only come up with papers from the "pro-mirror matter" camp. Unfortunately I can't access the paper, but I take it from the abstract that the mirror matter hypothesis contradicts the results of particle physics experiments.

From what I'd gathered previously, I thought the idea was that matter and mirror matter don't experience both normal and shadow forces, but either one or the other, evidently I'd made a mistake there...

Further elaboration would be nice, thanks

Oh dear; here is an abstract of a paper about a search for mirror matter - but I am afraid I understand hardly one word. Perhaps Fridger might be able to translate...

http://arxiv.org/abs/hep-ex/0311031

Mirror Matter as Dark Matter?

Let me first explain a bit from a particle physicist's point of view what people led to suggest the existence of Mirror Matter and why it's not very popular among particle physicists.

A major "design-tool" in theoretical physics has always been the requirement for symmetries that either hold exactly or are only weakly broken in the real world. The chain of arguments that led to the possible existence of Mirror Matter is quite analogous to what led to Supersymmetric particles, although Supersymmetry (SUSY) and Mirror Matter have nothing to do with each other.

SUSY is an elegant symmetry that transforms so-called "Bosons" (integer spin) into Fermions (half-integer spin). E.g. quarks, electrons, ... are Fermions, while photons, gluons gravitons are bosons. The expression "boson" and "fermion" refers to Bose statistics and Fermi statistics which the respective particles obey.

++++++++++++++++++++++++++
Once you insist the world to be supersymmetric, you need to require for all known elementary particles the existence of a respective SUSY partner particle the spin of which differs by 1/2 unit.
++++++++++++++++++++++++++

Hence the requirement of Supersymmetry led to the postulate of lots of new species of matter! Some of these SuSY partners are the presently most favored candidates for Dark Matter! (The so-called neutralinos).

However, SUSY is particularly popular because it provides a number of crucial benefits besides just predicting new kinds of particles.

1) Once the LHC super collider (CERN, Geneva) starts operating in 2008, we will SURELY know whether SUSY particles exist!

2) SUSY has a marvelous "stabilizing" property that theorists urgently want, in order to understand the huge existing hierarchies of fundamental scales!

3) SUSY is an essential property of String theory, the candidate "theory of everything". So SUSY fits to our "grand view"...

4) The SUSY particles interact by the SAME forces as their non-SUSY partners. So NO new forces required.

5) The idea of Grand Unification of all forces quantitatively needs the existence of the additional superpartner particles, since otherwise the strenghts of the various forces (strong, electromagnetic and weak) would not become equal at one SINGLE value of energy!

Next let me contrast that situation to MIRROR MATTER:
---------------------------------------------------------
Also here a symmetry requirement is at the origin: The requirement is that our theory is to respect spacial reflection symmetry or "Parity" as we say (x -> -x, t-> t). It is well known that despite it's great success, the weak-interaction sector of the "Standard Model of Elementary Particles" does NOT respect mirror symmetry. Besides parity, also other discrete symmetries are violated.

If you INSIST to have parity invariance, you MUST redouble essentially everything : the left-handed fermions need new right-handed "mirror" fermion partners etc. Unlike SUSY, you also need to redouble ALL forces, such that the only force that is felt both by normal matter and mirror matter is the extremely weak gravity! By action of gravity, mirror matter can equally condense and form galaxies, planets, asteroids and what not...The science press has been getting quite excited about this

However, there are NO other theoretical benefits of mirror matter, besides being a candidate as well for dark matter! The rest of the story in particle physics is therefore quite unattractive with lots of new VERY baroque new particles AND doubled forces.

Also --unlike SUSY-- we will have NO good chance to experimentally verify or disprove the existence of MirrorMatter in the laboratory!

One of the main proponents for Mirror Matter as Dark Matter has been /astrophysicist/ Robert Foot from U. Melbourne/Au. There are virtually NO renowned particle physicists who take the proposal very seriously.

Let me break here...I got to go for now...
Edited a bit further after returning...


Bye Fridger

eburacum45 wrote:Oh dear; here is an abstract of a paper about a search for mirror matter - but I am afraid I understand hardly one word. Perhaps Fridger might be able to translate...

http://arxiv.org/abs/hep-ex/0311031

Well that's an interesting story, also demonstrating that MirrorMatter is a dieing concept these days.

That paper is superseeded ~ 1/2 year later by another proposal of that group based on a refined apparatus to search for the invisible decay of orthopositronium in vacuum.
http://arxiv.org/pdf/hep-ex/0404037


The interesting aspect is this: while the earlier paper above was still completely motivated by the search for mirror dark matter, half a year later that possibility was only mentioned in passing!

The new experiment (using the same principle) was generally advertised to look for New Physics including "extra space-time dimensions", "fractionally charged particles" or new "light (gauge) bosons". It appears highly doubtful whether this proposed experiment will ever be done. The Zurich group is presently engaged with the ICARUS collaboration: The physics program of the collaboration is to study neutrino oscillations with the long base line neutrino beam from CERN to the Gran Sasso laboratory (CNGS), atmospheric, solar and supernova neutrinos, and a sensitive search for nucleon decays.

Bye Fridger

Thank you for your reply.
I already had the impression that Mirror Matter was out of favour-
not that it has ever really been in favour, by the looks of it.

But the SUSY stuff looks more promising, and there may soon be evidence one way or the other.