# Is dark matter a sea of massive photons?

Is the "missing mass" the mass of the photons connected to and neighboring the matter which are displaced by the matter?

phinds
Gold Member
Is dark matter a sea of massive photons?
This doesn't even make sense. There is no such thing as a "massive" photon. Photons are massless.

Is the "missing mass" the mass of the photons connected to and neighboring the matter which are displaced by the matter?
I can't make any sense out of this sentence but I'm sure the answer is no.

This doesn't even make sense. There is no such thing as a "massive" photon. Photons are massless.

I can't make any sense out of this sentence but I'm sure the answer is no.
Massive Photon and Dark Energy
https://arxiv.org/abs/1512.00541

PeterDonis
Mentor
2020 Award
Massive Photon and Dark Energy
I have not read the paper in detail, but one thing strikes me from the abstract: it is using "the scalar-vector-tensor theory of gravity", which AFAIK is ruled out by experiment unless the "scalar" and "vector" parts are given coupling constants so small as to be negligible. So even though a photon mass is used which is smaller than the current upper bound from experiment, this theory still seems to me to have a problem because of the theory of gravity that is used.

phinds
Gold Member
Could the "missing mass" associated with dark matter actually be the mass of the particles displaced by the matter?
I still can't figure out what you mean by that. What particles displaced by what matter?

Garth
Gold Member
We can do a bit better than that with the original question.

Photons are generally thought of as massless although some heterodox theories such as that discussed in Massive Photon and Dark Energy suggest they may have a small mass:
the nonvanishing photon mass of the order of 10 - 34eV is consistent with the current observations. This magnitude is far less than the most stringent limit on the photon mass available so far, which is of the order of m<=10 - 27eV.
Let us limit our discussion to that paper, which should focus, amongst other things, on the status of the "the scalar-vector-tensor theory of gravity". Peter have you a reference(s) to your statement that it "is ruled out by experiment unless the "scalar" and "vector" parts are given coupling constants so small as to be negligible"?

Garth

ChrisVer
Gold Member
I am not sure, but even if photons had a mass below the excluded by experiment region let's say $10^{-27}eV$, then the photons are still supposed to be radiation (under cosmology), so at best they could account for HDM and not CDM.

Garth
Gold Member
I am not sure, but even if photons had a mass below the excluded by experiment region let's say $10^{-27}eV$, then the photons are still supposed to be radiation (under cosmology), so at best they could account for HDM and not CDM.
But the paper discusses whether photons with a small mass could explain Dark Energy not Dark Matter.

The original question was confused, yes, and if such photons are thought to be DM, not DE, then that, as Hot Dark Matter, has been ruled out. Basically HDM wouldn't clump as required to form the obsertved large scale structure.

So the question remaining is, "Can photons with a small mass explain Dark Energy?"

Garth

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PeterDonis
Mentor
2020 Award
Peter have you a reference(s) to your statement that it "is ruled out by experiment unless the "scalar" and "vector" parts are given coupling constants so small as to be negligible"?
I'm going by what I have seen in textbooks such as MTW, which IIRC discusses this in some detail. As I remember it (don't have my copy handy to check), various solar system tests, such as light bending by the Sun, rule out significant scalar or vector terms in the Lagrangian. The paper that the OP linked to talks about comparisons with cosmological data, but does not talk at all about consistency with other data such as solar system tests.

PeterDonis
Mentor
2020 Award
even if photons had a mass below the excluded by experiment region let's say ##10^{-27}## eV, then the photons are still supposed to be radiation (under cosmology), so at best they could account for HDM and not CDM.
I agree if we are using GR as our theory of gravity. The paper the OP linked to talks about a different theory of gravity, a "scalar-vector-tensor" theory, which can produce different behavior of photons, theoretically speaking. However, as I've noted in other posts, I don't think that theory of gravity is consistent with other experimental data (such as solar system tests).

George Jones
Staff Emeritus
Gold Member
I agree if we are using GR as our theory of gravity. The paper the OP linked to talks about a different theory of gravity, a "scalar-vector-tensor" theory, which can produce different behavior of photons, theoretically speaking.
I am not sure about this. The introduction seems to say that it is QED that is modified, not GR:

The theory consists of massive vector field and Stuckelberg scalar field interacting with Einstein gravity.

PeterDonis
Mentor
2020 Award
The introduction seems to say that it is QED that is modified, not GR
Yes, I saw this, but elsewhere they say they are using a "scalar-vector-tensor theory of gravity". It also looks to me like the effective Lagrangian they are using contains terms involving the curvature other than the Einstein-Hilbert term. So I think that by "Einstein gravity" they just mean "a spin-2 tensor field", not "exactly GR". But I am not familiar with the field theories they are drawing on and probably need to spend some time with the references in the paper to increase my background knowledge.

Garth
Gold Member
I'm going by what I have seen in textbooks such as MTW, which IIRC discusses this in some detail. As I remember it (don't have my copy handy to check), various solar system tests, such as light bending by the Sun, rule out significant scalar or vector terms in the Lagrangian. The paper that the OP linked to talks about comparisons with cosmological data, but does not talk at all about consistency with other data such as solar system tests.
The TeVeS theories were proposed after MTW was published and are not inconsistent with solar system tests, papers can be found here: The Tensor-Vector-Scalar theory and its cosmology and A tensor-vector-scalar framework for modified dynamics and cosmic dark matter except, as that latter paper proposes, the MOND increase (over Newtonian/GR gravity) of gravitational sun-wards acceleration at large radii in the outer solar system would be interpreted as a Pioneer type anomaly.

Basically the scalar and vector terms of TeVeS, and indeed in $\Lambda$CDM DE, are too small to be detected at small solar system distances and only become significant over 'large' ranges so they only would become detectable by Pioneer in the outer Solar System.

Papers are still being submitted about MOND/TeVeS theories such as on today's ArXiv: Dynamics of Elliptical Galaxies with Planetary Nebulae in Modified Newtonian Dynamics and Highly compact neutron stars in scalar-tensor theories of gravity: Spontaneous scalarization versus gravitational collapse so it is not yet a dead duck!

The Bullet Cluster poses a greater problem for TeVeS theories as investigated here: Asymmetric gravitational lenses in TeVeS and application to the bullet cluster with the conclusion that
TeVeS cannot explain observations without assuming an additional dark mass component in both cluster centers, which is in accordance with previous work.
So Dark Matter is still required in some form, although perhaps not to explain galaxy rotation rates.

Garth

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PeterDonis
Mentor
2020 Award
@Garth: Interesting papers, I'll take a look! I am not very familiar with this area of research.

Chronos
Gold Member
I still think TeVes is a mathematical cluster of hooey.

Garth
Gold Member
I still think TeVes is a mathematical cluster of hooey.
I agree but some might say that about the $\Lambda$CDM theory, what with the undiscovered dark sector, the coincidence problems - $\Omega_M \sim \Omega_\Lambda$, $\Omega_m + \Omega_{DM} + \Omega_\Lambda = 1$ , Age of Universe = H-1, and built on GR which has proved so far incompatible with quantum theory.

I think there is enough wriggle room to ask questions about it all.
Garth

Chronos