Energy of Dark Matter

[PhanthomJay]

I know that Dark Matter and Dark Energy are 2 different animals. My question is not related to the difference between the 2. My question is, if dark matter exists, and since matter has energy, then dark matter must have energy associated with it. So while I hear a lot about Dark Energy and Dark Matter, I hear nothing about the 'Energy of Dark Matter'. Except from the Brane Theorist's possible explanation that dark matter is gravitational energy from other Universes. But if Dark Matter consists of WIMP particles, what's the energy of such a postulated particle? Would it be the same as the energy of an 'ordinary' particle, like kinetic energy, or E =mc^2 energy?

[nicksauce]

Yes, people generally take the energy of dark matter to be E=mc^2. Any sort of kinetic component is generally ignored, because these days most people believe that dark matter is "cold", in the sense that its rest energy is much greater than its kinetic energy, and has been for most of the lifetime of the universe.

[PhanthomJay]

Thank you! Now since dark matter energy cannot be called dark energy, since the 'dark energy' definition has already been established, is there a name for it besides "Dark Matter Energy"? Also, are 'Dark Energy' and 'Vacuum Energy' the same (synonyms)?

[nicksauce]

It's not really something people talk about a lot, so I don't think there's a term that is generally used for it. "Dark matter energy", or the "energy of dark matter", seem fine to me.

Dark energy is the thing that's responsible for the accelerated expansion of the universe. Vacuum energy is the energy of the vacuum (obviously). It is thought that vacuum energy could be what is causing the accelerated expansion, though there are other candidates, such as a scalar field, or some kind of geometrical effect. So I wouldn't say that they are synonyms.

[Chalnoth]

Yes, people generally take the energy of dark matter to be E=mc^2. Any sort of kinetic component is generally ignored, because these days most people believe that dark matter is "cold", in the sense that its rest energy is much greater than its kinetic energy, and has been for most of the lifetime of the universe.
Well, it's not just that people believe it, but observationally this is necessarily the case. Now, it may potentially have had some noticeable temperature in the early universe, these investigations are still underway, but it was most definitely not relativistic at the emission of the CMB, and thus its temperature didn't make for a significant contribution to the energy density.