WIMPs and the standard model.

[howlingmadpanda]

Recently as I was reading a book concerning Theoretical Dark Matter I came upon a question which bothered me, but I could not find and answer to it. The question is as follows: If Dark Matter and Dark Energy were confirmed would "Dark particles" be added to the standard model? And would Dark Energy be classified as a fifth force? And for the final question: What would become of any Weakly Interacting Massive Particle on the standard model, would a new model be created, or would it just be added? I'm guessing that any particle would be as all other forces are explained by the Standard model, any thoughts would be greatly appreciated/

[ajb]

If dark matter turns out to be a particle not included in the standard model then it will need to be added to some extended version of the standard model. I think that the idea that dark matter is a standard neutrino is now seen as unlikley. So it does look like dark matter is some other particle outside the standard model.

 

One such extension could be the minimal supersymmetric standard model, or it could be something more exotic again.

[J.C.MacSwell]

What evidence is their that there may be dark particles, rather than, say, a necessary adjustment to gravitational theory based on the detectable mass and energy that we know is there?

 

For instance, do we see any spiral arms with significant gaps that we can point to and ask; what is holding that together?

 

Or, how sure are we of the distances we are basing the calculations on, and could at least some of the required dark matter required be explained in this way?

[timo]

I think the evidence is the large number of observations fitting the assumption, as probably discussed on Wikipedia (http://en.wikipedia.org/wiki/Dark_matter#Observational_evidence , didn't read the actual article, though). The most interesting evidence I heard about was the Bullet Cluster observation (http://en.wikipedia.org/wiki/Bullet_Cluster).

[J.C.MacSwell]

Reading some of the Wiki suggested by Timo I found this in one of the links:

 

"The visible disk of the Milky Way Galaxy is embedded in a much larger, roughly spherical halo of dark matter. The dark matter density drops off with distance from the galactic center. It is now believed that about 95% of the Galaxy is composed of dark matter, a type of matter that does not seem to interact with the rest of the Galaxy's matter and energy in any way except through gravity. The luminous matter makes up approximately 9 x 1010 solar masses. The dark matter halo is likely to include around 6 x 1011 to 3 x 1012 solar masses of dark matter.[6]"

 

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

 

It mentions the halo being "roughly spherical". How would it manage to maintain a spherical shape?

[Enthalpy]

The Bullet cluster is an evidence for dark matter, against modified gravitation. Though, dark matter isn't necessarily particles. Other constituents have been proposed and aren't completely abandoned as far as I know. Brown dwarves are strongly disfavoured presently, as are cold star remnants, but others may still be possible.

 

Fun: at the bullet cluster, ordinary matter is observed where it is expected after a collision of two galaxies, and so is weakly interacting dark matter... But meanwhile 2-3 more galactic collision remnants were observed for the same microgravitational lenses, and there the dark matter was NOT where expected... Men think and God laughs.

 

At least, this was a disappointment to people who already hoped to have a complete explanation through weakly interacting dark matter. But certainly not an argument in favour of modified gravitation, since microlensing is seen in every case.