What is Dark Matter?

[velo]

I admit i have reached a dead end in my search for a Dark Matter candidate,

is there some one who has a deeper understanding of the topic ,and is

willing to enlighten me with his/her knowledge as to what Dark Matter is?

[swansont]

If we knew specifically what it was, it wouldn't be called dark matter. That's the placeholder name given to whatever is responsible for the observed deviation from known physics in galactic behavior.

[Klaynos]

Last time I read anything about it I think lots of people where saying WHIMPS where a big candidate, but there are other people saying that that is wrong.

[Royston]

velo, this is the most recent article I could find on the subject, though I don't think it's really what you're after...you may as well check wiki (link below) there are several candidates for dark matter, but AFAIK nothing has been settled as of yet...

 

http://www.sciencedaily.com/releases/2007/04/070419130004.htm

 

http://en.wikipedia.org/wiki/Dark_matter

[timo]

Last time I read anything about it I think lots of people where saying WHIMPS where a big candidate.

The term is WIMP without and H and stands for "weakly interacting massive particles". The term, however, is also generic to some extent. It refers to electrically uncharged (hence not interacting via photons but at most via the "weak force" and of course gravity) massive particles - where I think (but do not know for sure) "massive" also means a relatively high mass. But it doesn´t necessarily mean a specific particle and isn´t bound to a specific exotic physics model.

 

As a follow-up question: Does anybody know for sure if warm dark matter (meaning light particles) is still an option or is it ruled out by now?

[Severian]

WIMPS are sometimes called 'cold dark matter'. The other traditional dark matter possibility was 'Hot dark matter' which has indeed now been ruled out.

 

Whether or not something is 'hot' or 'cold' is dependent on whether or not it is in thermal equilibrium with the universe. If a particle is very light, then the temperature of the universe (ie. the average energy of the photons floating about from the CMBR) is high enough that they can be created (usually in matter-antimatter pairs) and annihilated at will. They are in thermal equilibrium.

 

If the particle is very heavy, then it takes so much energy to create them that it basically never happens. So they are out of thermal equilibrium.

 

Experiments like WMAP have now shown that Dark Matter is cold.

 

The most favoured candidate these days is the "neutralino" which is a stable particle of about 100GeV in many supersymmetry scenarios. This can account for dark matter pretty well.

 

We should find out next year when the LHC switches on (assuming the Americans don't blow it up again).

[Klaynos]

The term is WIMP without and H and stands for "weakly interacting massive particles".

 

And I knew that... a document I was writing around making that post has lots of words in it where I've only written one letter of the word and then moved on... was an interesting morning.

 

Apologies people.

[velo]

http://web.mit.edu/~redingtn/www/netadv/specr/6/node1.html

 

This page will show why the chance of finding WIMPs is remote.

 

I dare say some will keep on flogging the dead horse.

[velo]

http://www.cosmosmagazine.com/node/714

 

And this one.

 

Supersymmetry is a theory that predicts a 'super' partner for every known particle (and antiparticle). While supersymmetry is a well-founded theory, the exact mathematical details are disputed among the scientific community.

 

The more popular models of supersymmetry predict a much higher transition rate than three trillion times per second. This is a serious blow to particle physicists, as these popular models will now have to be reconsidered.

 

And it's hard to challenge these new findings: the physicists are 99.99999992 per cent sure that they're right.

[Severian]

http://www.cosmosmagazine.com/node/714

 

And this one.

 

Supersymmetry is a theory that predicts a 'super' partner for every known particle (and antiparticle). While supersymmetry is a well-founded theory, the exact mathematical details are disputed among the scientific community.

 

The more popular models of supersymmetry predict a much higher transition rate than three trillion times per second. This is a serious blow to particle physicists, as these popular models will now have to be reconsidered.

 

And it's hard to challenge these new findings: the physicists are 99.99999992 per cent sure that they're right.

 

I presume you are refering to this paper? http://arxiv.org/abs/hep-ph/0603106

 

Flavour changing neutral currents have always been know to be a problem for supersymmetry. But they do not rule it out - just restrict the parameter space.