# B Dark photons

1. Nov 8, 2017

### star apple

If there were dark photons in the dark matter sector.. should it be described by gauge symmetry.. in other words.. should the dark photons be gauge bosons? or nongauge bosons just like the higgs?

2. Nov 8, 2017

### Staff: Mentor

What are "dark photons"? Do you have a reference?

3. Nov 8, 2017

### strangerep

Light that is not light? A particle that should be called a "darkon"?

I'll go out on a limb and bet this is a load of nonsense.

[Edit: Yep, my bet is looking good. ]

Last edited: Nov 8, 2017
4. Nov 8, 2017

5. Nov 8, 2017

### Staff: Mentor

As is typical, this article does not link to any actual papers. I find some papers by Googling "dark photon site:arxiv.org", but the general impression from a quick skim of these is that this is a highly speculative model (or class of models--there seem to be a number of hypothetical proposals) which will not be easy to test.

It looks like the hypotheses that go by the name "dark photon" are called that by analogy with electromagnetism: they basically propose a new U(1) gauge boson that mediates an interaction between some type of dark matter (the models for that appear to vary) and ordinary matter. On a quick skim I don't see any hypotheses that don't involve that gauge symmetry. (Such a model is easy to construct, which is probably why theorists trying to find dark matter are trying these kinds of models first.)

6. Nov 8, 2017

### star apple

I think dark photon doesn't mediate the interaction between some type of dark matter and ordinary matter. Dark photons seem to a term reserved only for interaction between dark matter themselves..

https://www.scientificamerican.com/article/new-theories-dark-matter/
"A group of researchers at the California Institute of Technology proposes that dark matter could have its own force analogous to electromagnetism—mediated, naturally, by "dark photons". Just as in regular electromagnetism, the force would act over long ranges, and the photon (the discrete unit of light energy) would be massless. As noted by study co-author Sean Carroll, a Caltech physicist, on the blog Cosmic Variance, the theory opens the door to a rich, as yet unseen world of dark radiation, even dark magnetic and electric fields."

Here's the paper... https://arxiv.org/abs/0810.5126

dark photon seem to be based on gauge symmetry like U(1).. please share paper where it is not based on gauge symmetry.. remember Witten propose gauge symmetry is emergent.. so I wonder if dark matter sector is more primary to matter? what theoretical arguments or cosmological observation can rule this out?

7. Nov 8, 2017

### Staff: Mentor

The term might be used to refer to both kinds of models. It seems to be a pretty general term, not a name for a single specific model.

As I said in my last post, I'm not aware of any.

8. Nov 8, 2017

### star apple

somewhere inside it is mentioned dark atoms

"Although one must be very cautious to not overinterpret the
correspondence, the proposed situation is broadly similar to postulating
a dark proton, a dark electron and a dark photon to carry
the dark electromagnetism that binds them together. Depending
on the mass and charges of the dark fermions, they could
combine to create dark atoms with their own dark chemistry,
dark molecules and possibly even more complex structures. The
concept of dark atoms was explored in detail in 2010 by David E.
Kaplan, Gordan Z. Krnjaic, Keith R. Rehermann and Christopher
M. Wells, all then at Johns Hopkins University.

The Harvard physicists who proposed the dark matter fermions
idea went on to derive an upper limit on the fraction of dark
matter that may be strongly interacting with dark photons, given
the constraints imposed by astronomical observations. They determined
that its cumulative mass may be as large as that of all
visible matter. In this model, the Milky Way galaxy consists of a
large spherical cloud of WIMP-like particles, which contributes
70 percent of the total matter, encircling two flattened disks, each
containing 15 percent of the matter. One disk is normal matter,
which includes the spiral arms that we can see, and the other consists
of strongly interacting dark matter. The two disks need not
be exactly aligned, but they would have a similar orientation. In
this picture, a dark matter galaxy basically coexists in the same
space as our familiar Milky Way. A cautionary note: the dark
matter galaxy would not include dark stars or large planets, because
these would have been observed through their gravitational-
lensing effects on ordinary matter."

All right. Anyone can show any cosmological observation that can refute it? It's saying 70% of universe is non interacting dark matter (or very weakly).. and 15% are strong interacting dark matter enough to form dark galaxy and 15% is normal matter. This was proposed by David E.
Kaplan, Gordan Z. Krnjaic, Keith R. Rehermann and Christopher M. Wells, all then at Johns Hopkins University.

I hate the idea of dark galaxy and dark planet and dark people. So please show any updated paper that refute them. Thanks.

9. Nov 8, 2017

### Staff: Mentor

Sorry, your personal feelings about a theory are irrelevant to whether it's correct or not. And you've already been told that all of these models are speculative and will not be easy to test; certainly asking for an "updated paper that refute them" is premature at this point. This is an open area of research, and looking for definitive answers is simply not going to get you anywhere.

10. Nov 9, 2017

### Orodruin

Staff Emeritus
Dark photons are a common component in an extended dark sector. It is a generic name for the gauge boson of a dark $U(1)$, i.e., a new Abelian gauge group under which only particles in the dark sector are charged.

Even if introduced as a gauge group that only couples to the dark sector, models including a dark $U(1)$ generally lead to very weak interactions with Standard Model matter via mixing of the dark photon with the photon. This also leads to concepts such as millicharged dark matter.

This is the publication page of the NA64 collaboration. Essentially they are trying to shine light through a wall, which would be partially possible if the photon mixed with a dark photon.

Nobody has proposed that this would be the case even in a dark sector with both dark photons and dark atoms. Dark matter must still behave very differently from ordinary matter. In particular, you are completely ignoring this passage:

11. Nov 9, 2017

### Staff: Mentor

Moderator's note: I allowed @Orodruin to add his post since it contains useful information about these types of models. The thread will remain closed.