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I saw a news from an official MIT website about a hypothesis proposed by MIT scientists which "massive photons" could be the sources of dark matter. They've also proposed an experiment for proving their theory.

Here is the news from MIT: http://news.mit.edu/2013/dark-matter-1025

Is it possible? Any idea?

In addition, the term "massive photon" has been used in the above article (in 3rd, 4th, 5th and 6th paragraphs) by MIT professors of physics directly. In particular, in the 4th paragraph has been written:

"Now, an experiment known as DarkLight, developed by Fisher and Milner (MIT professors) in collaboration with researchers at the Jefferson National Accelerator Laboratory in Virginia and others, will look for a massive photon with a specific energy postulated in one particular theory about dark matter, Milner says."

It seems that by "Dark-Light" they mean a sort of light that includes massive particles which should be new massive bosons (or as MIT physicists called them "massive photons") carrying the electromagnetic force (?). Any idea (in theoretical point of view)?

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    $\begingroup$ I am not interested in answers which are unrelated to the main question. Please note that the question is about "DARK MATTER" and its relation to some hypothetical massive particle (so-called "massive photon" by MIT Professors of Physics). In particular, the question is not about the term "massive photon" and how it gives the journalists a rough idea.. and so on. Moreover, the question doesn't concern some unnecessary general issues such as 'the Higgs boson is a boson' and so on. It would be also fine if you don't repeat (as answer) some notes which have been exactly mentioned in the article. $\endgroup$
    – user130644
    Sep 24, 2016 at 8:37
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    $\begingroup$ original paper here arxiv.org/abs/1305.0199 $\endgroup$
    – anna v
    Sep 25, 2016 at 10:48

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First of all, note that the news article is from October 2013 and so it is somewhat outdated. However the experiment was actually scheduled to start in summer 2016 at the Jefferson Lab, and so the results are yet to come. I took a quick look at the paper linked in the news article and the words "massive photon" do not appear anywhere. Instead they refer to the search of a "new boson" at some point. So it is quite likely that the expression quoted in your link is just an easy way to give the journalists a rough idea of what kind of particle these scientists are looking for. It is not related in any way with the photons we all know, but it just shares with them some properties.

The particles with integer spin are called bosons, because they follow the Bose-Einstein statistics. Photons are bosons, the Higgs boson is a boson (!), and the new particle they are looking for is supposed to be a boson. All the known bosons are included in the Standard Model and, with the exception of the Higgs, play the role of carriers of three of the fundamental forces (electromagnetic, weak and strong). The new particle that they hope to find with this experiment is not predicted by the Standard Model, and therefore its detection would lead to "new" physics. It is quite common that, within several different theoretical frameworks, new particles are conjectured in order to explain the origin of dark matter, but so far no attempt has proved successful. We'll see how this goes!

Back to the actual question: the experiment is aimed at finding a new massive gauge boson, called $A'$ in the literature, with mass in the range $0.01-10$ GeV. One theoretical model that describes how this new dark matter candidate could arise is explained in detail in this paper, and a more readable summary of how this could relate to current astrophysical observations can be found in section A of the research proposal for the experiment. I suggest to check these two resources for detailed information on the subject. The general idea behind this theory is that the dark matter itself is constituted by very massive ($\sim$TeV) particles, which are therefore out of the reach of experiments (The current LHC energy might actually be borderline, but no results have been obtained so far). So far, this is no different from many other theories of dark matter, including the ones that want to identify the new particles with the supersymmetric partners of known particles. The difference, however, is that while the most common idea is that these massive particles interact through the weak force -the so called WIMPS- in this case the interaction takes place due to a new "fifth force" mediated by a new massive $U(1)$ gauge boson, the "Dark Photon".

According to this theory the $A'$ is kinetically mixed to the Standard Model $U(1)_Y$, which means that in the Lagrangian we have a term of the form $$\mathcal{L}_{mix}=\frac{\kappa}{2}V^{\mu\nu}B_{\mu\nu}$$ where $\kappa$ is a parameter that determines the amount of mixing and $V^{\mu\nu}$ and $B^{\mu\nu}$ are the field strength built from the "Dark" and "normal" photon fields respectively. In short, this means that the "dark photon" interacts with matter in a way which is very similar to the traditional photon. In particular it implies that it can decay into electrons, muons and pions and this could possibly justify some excesses in the production of these particles revealed by previous astrophysical observations.

One great hope of the scientists was that this could provide a solution for the anomalous magnetic moment of the muon puzzle, but unfortunately this possibility has been largely ruled out by other experiments, see for example this. To conclude, it seems that the presence of a "dark photon" would not be inconsistent with other observation, but this would require a certain amount of fine-tuning of the parameters of the model and fails to explain one of the phenomena that was at the basis of its proposal.

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    $\begingroup$ @DelCrosB Usually, if the OP has questions or needs clarification, the OP should add a comment to the post in question. The typical way of responding depends. If it's brief and the clarification adds little to the answer, you can respond with another comment. If it's longer or you feel it would benefit the answer, you would edit your answer with additional content or edit the content to be more clear; you would typically notify the OP to see the updated answer once you're done. You don't need to call out your edits in a separate section; you can just include the changes in the normal flow. $\endgroup$
    – jpmc26
    Sep 22, 2016 at 21:58
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    $\begingroup$ @DelCrosB Your answer is unrelated to the main question. Please note that the question is about "DARK MATTER" and its relation to some hypothetical massive particle (called "massive photon" by MIT Professors of Physics). The first part of your answer is about the term "massive photon" and how it gives the journalists a rough idea.. (!?). In the 2nd paragraph of your answer you noted some general information about bosons such as 'the Higgs boson is a boson' , and so on . Your note about the Standard Model and a "new physics" also has been exactly mentioned in the 6th paragraph of the article. $\endgroup$
    – user130644
    Sep 23, 2016 at 3:52
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    $\begingroup$ @Newmann, I think the point that DelCrosB is making is that the term "massive photon" is somewhat misleading, because it creates the impression that the photon that we know from EM theory has a mass. This would of course be nonsense. The source of this confusion seems to lie with the news article. The MIT scientists are actually looking for a new force, which is different from the EM theory we known, and which has a massive boson associated with it. $\endgroup$
    – flippiefanus
    Sep 23, 2016 at 4:55
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    $\begingroup$ @DelCrosB you won't usually see people making suggested edits in order to communicate with you. Most people will just leave a comment, but users with less than 50 reputation cannot comment on your post, which sometimes leads to people trying alternative approaches like this. $\endgroup$
    – trichoplax is on Codidact now
    Sep 23, 2016 at 12:03
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    $\begingroup$ I deleted a few inappropriate comments and their responses. Anyway, whenever you edit your answer, it's best to change it to make it appear the way you wish you'd written it from the beginning. Don't mark your edits with "UPDATE:" or "EDIT:" or the like. (It's not the worst thing, it's just very much not recommended.) $\endgroup$
    – David Z
    Sep 24, 2016 at 15:45
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It is an onion: the mit article refers to an experimental paper and the experimental paper to a proposed detector for finding dark matter:

We give a short overview of the DarkLight detector concept which is designed to search for a heavy photon A' with a mass in the range 10 MeV/c^2 < m(A') < 90 MeV/c^2 and which decays to lepton pairs. We describe the intended operating environment, the Jefferson Laboratory free electon laser, and a way to extend DarkLight's reach using A' --> invisible decays.

Here is where the "photon" comes, and yes, it will be a boson interacting electromagnetically, but with a mass. The onion has a further layer,

6.2.2 Hidden-Sector Photons

This section describes the theory and motivation for new forces mediated by new abelian U(1) gauge bosons A0| also called "U-bosons," or "hidden-sector," "heavy," "dark," "para-," and "secluded" photons | that couple very weakly to electrically charged particles through "kinetic mixing" with the photon .

Further reading of the references is needed to get at the maths.

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