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Definition: Radiation in this case does not refer to electromagnetic radiation. It refers to any kind of emission of energy, even energy that does not interact with regular matter.

Just like dark matter does not interact with electromagnetic radiation, could regular matter not interact with "dark matter radiation" (I'm not talking about the usual "really high wavelength radiation" kind)?

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Obviously these kinds of things can't be ruled out unless and until we find a way to study the dark matter. Currently we have data only from very indirect approaches (mostly cosmological comparisons of calculated lumpiness to observations). –  dmckee May 3 '12 at 19:13
This is a very interesting question though. What could be a possible way to go about testing it? –  Nico Bellic May 3 '12 at 22:35
Experiments attempting to detect dark matter in two different non-gravitational ways (imaginatively called "direct" and "indirect") are underway. Assuming success further studies will be planned. –  dmckee May 3 '12 at 22:40
Wouldn't this show up as a straightforward (but perhaps difficult to measure) effect in the matter power spectrum? I.e., wouldn't it make the dark matter tend towards "warm" or "hot" rather than cold? I think that's what @dmckee is hinting at, and I wonder if there are some robust constraints in place already. –  kleingordon May 4 '12 at 9:20
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4 Answers 4

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It's actually a bit unlikely for the following reason:

Dark matter is observed to not 'clump' as effectively as ordinary matter. This is due to the fact that ordinary matter feels drag due to interactions with the intergalactic dust and loses angular momentum to radiation, causing it to fall inward toward the galactic core, and to fall toward a central disk that is prevented from further collapse due to conservation of angular momentum.

Dark matter, however, is observed to maintain an approximately spherical distribution, rather than mirroring the external disk, and is thus expected to be immune to the interactions that caused the visible matter in, say, the milky way to flatten and fall a bit inward. since the majority of the matter in most galaxies is dark matter, if the dark matter interacted with itself in such a way that "dark radiation" was produced, you'd expect qualitatively similar behaviour to the ordinary matter.

That said, I'm sure you could construct models that worked.

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In fact, simulations of galaxy formation leads to much denser cores at the center of galaxies than what is observationally seen. One of the proposals for resolving this conflict is to allow for interactions amongst dark matter particles - precisely what you are looking for. The original (to my knowledge) paper is arxiv.org/pdf/astro-ph/9909386v2.pdf –  contrariwise Mar 29 '13 at 4:50
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In order to address the question :

Just like dark matter does not interact with electromagnetic radiation, could regular matter not interact with "dark matter radiation" (I'm not talking about the usual "really high wavelength radiation" kind)?

One needs experimental evidence, as @dmckee 's comment suggests.

The other tack is to find a Theory Of Everything which describes experimental data in particle physics and check whether there are predictions for dark energy and dark matter behavior in specific models which will address the interactions of dark matter with the known matter.

The only consistent candidate models are based on string theory, which allows for the quantization of gravity and for the inclusion of the known data as described by the standard model of particle physics.

Various models based on strings have candidate new particles for dark matter and will have coupling constants for computing the interaction of these dark matter candidates with radiation fields that the theory allows. These models have predictions that may be realized in the experiments now running at the LHC at CERN, and if they are confirmed, then the question of interaction of normal matter and dark matter will also be addressed by the model.

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Well, I claim the answer is yes! Since the question defines radiation as emission of energy that doesn't interact with normal matter, I say that dark matter emitting dark matter particles qualifies as emission of energy that doesn't interact with normal matter. An clearly it can do that.

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What particles do you claim it can emit? –  Benjamin Horowitz Aug 3 '12 at 21:09
@BenjaminHorowitz: Are there no theories of dark matter where a dark matter particle can decompose into smaller dark matter particles? Even if not, any dark matter particle that leaves a larger collection is an "emission" that carries "energy". –  ThePopMachine Aug 6 '12 at 20:34
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Yes, just as you have bosons mediating interactions in the Standard Model sector, you could have dark radiation mediating interactions in the DM sector. Given that more energy is in the form of DM than SM particles, this won't be surprising. Of course, one needs proof for such a species of particles to exist :) A particle physics approach would be to understand the exact nature of the DM particle and its interactions. A cosmological approach would be to see if there are missing relativistic components, as in this paper.

By the way, by radiation, I hope you mean relativistic particles. It is in that sense that radiation is used in the cosmological context.

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