0
$\begingroup$

It is assumed that massless charged particles acquired mass after the early phase of the Big Bang. But could most charged particles be massless now as dark matter. They wouldn't interact with photons or electrons electromagnetically because electrons have mass and charge and photons are charge less massless Neither are charged massless

Improve this question
$\endgroup$
5
  • 4
    $\begingroup$ Dark matter particles (whatever they might be - axions, wimps something else...) must have mass, but no charge. So the can't be particle with charge but no mass. $\endgroup$
    – James K
    Commented Sep 19, 2023 at 22:30
  • 1
    $\begingroup$ I would dispute the claim that dark matter particles have mass. The cold dark matter solution has problems associated with it such as too few dwarf galaxies. The hot model also has problems but doesn't as yet consider charged massless particles. If charged massless particles are like gluons (massless with colour charge) they could self interact and hold each other together. $\endgroup$
    – user52290
    Commented Sep 19, 2023 at 22:44
  • 2
    $\begingroup$ But a key property of dark matter is that it has negligible self-interaction, apart from gravitation, which is due to mass. Haloes of such particles give the necessary mass distribution required to account for galaxy rotation curves. Charged massless particles would give a very different distribution. $\endgroup$
    – PM 2Ring
    Commented Sep 20, 2023 at 2:33
  • 8
    $\begingroup$ What would be the point/need for massless "dark matter"? $\endgroup$
    – ProfRob
    Commented Sep 20, 2023 at 9:50
  • $\begingroup$ see physics.stackexchange.com/questions/7905/… $\endgroup$
    – James K
    Commented Sep 20, 2023 at 17:28

2 Answers 2

Reset to default
7
$\begingroup$

Charged, massless particles would be a form of "hot" dark matter. i.e. A form of energy density that was relativistic at the epoch of structure formation and of course, still relativistic now, since massless particles travel at the speed of light. That is not what is needed to explain structure formation in the universe or the dynamical properties of galaxies and galaxy clusters now, which need "cold" (non-relativistic) dark matter.

However, a more fundamental problem appears to be that massless charged particles should not exist. If they did then electrons and positrons would quickly decay into their massless counterparts whilst conserving charge. Massless charged particles should also be rather easy to produce in particle accelerators and none have been observed. Indeed it should even be possible for "pair production" just to take place with everyday (visible) photons.

Improve this answer
$\endgroup$
4
  • $\begingroup$ (+1) Nice answer! $\endgroup$
    – Arjun
    Commented Sep 20, 2023 at 10:49
  • $\begingroup$ @ProfRob The charged massless particles would not have interacted with the Higgs field in the early universe for some reason .That reason may also be why electrons and protons now can't decay into them and why visible photons can't form charged pairs today .I should think that failure to interact with the Highs means a particle is carrying a quantum number (property) that is incompatible with the Highs field theory $\endgroup$
    – user52290
    Commented Sep 20, 2023 at 10:50
  • 5
    $\begingroup$ @DaveTheWave I gave an answer based on physics that is known. If you postulate physics from another universe then anything is possible. The reason I have given is essentially why muons are not common, everyday particles - all particles will decay to their least massive manifestation that does not violate conservation laws. $\endgroup$
    – ProfRob
    Commented Sep 20, 2023 at 11:09
  • $\begingroup$ Minor point: "hot dark matter" traditionally refers to stuff that is nonrelativistic today (hence "matter"), but transitioned relatively recently so that it has a long free-streaming length and low phase-space density. $\endgroup$
    – Sten
    Commented Sep 20, 2023 at 17:50
4
$\begingroup$

No, because if "dark matter" had no mass, it wouldn't be dark matter anymore.

Keep in mind dark matter needs to exert gravitational force, and massless particles do not exert gravitational force (at least not in the same way massive particles do).

If dark matter actually did have no mass, it would become "dark radiation", which behaves in a fundamentally different way (see Wikipedia's technical definition section for dark matter). It's possible that a small amount of dark radiation exists, but not a lot of it, and certainly not anywhere near the amount of dark matter in the universe (source).

Improve this answer
$\endgroup$
1
  • 1
    $\begingroup$ I don't agree that massless charged particles would behave like radiation . The charge makes them different to light and the masslessness different to baryons so they may not move at the speed of light or slower They must be faster than light! Dark matter is more complicated than we think. $\endgroup$
    – user52290
    Commented Sep 20, 2023 at 7:52

You must log in to answer this question.