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RE: Pinning down electrically-charged dark matter
I'm familiar with energy levels like electron volts being chemical reactions. Mega-electron volts being nuclear reactions. I guess giga-electron volts being degenerate matter reactions, or something? I don't know if I have those scales correct.
On the other hand, what would a milli-electron volt represent? I guess there's nothing in normal every-day life that would help us wrap our heads around such small scales of energy levels.
In particle physics, we work in a well-adapted system of units. The speed of light is taken equal to 1 and Planck's constant is also taken equal to 1 too. In this framework, the eV unit can also be used for the masses of the particle.
511 keV (511.000 eV) corresponds to the mass of the electron, and 1 GeV (or 1.000.000.000 eV) is the mass of the proton. The heaviest of all known particles, the top quark, has a mass of 175 GeV (i.e. 175 protons).
In LHC collisions (13 TeV, or 13.000 GeV, per collision), it is quite common that particles with energies of dozens or hundreds of eV are produced. The energy is however provided mainly under the form of kinetic energy.
Does it clarify?
Let's now move on with the second part of the comment.
Here, if you check the last figure, we consider electric charges of 10-18 to 10-7 times the charge of the electron. There is nothing like that in our everyday life, since anything charged has a charge given by an integer number of electron charges. How is this possible?
Here, the way the dark particles are sensitive to electromagnetism comes from another source (not their electric charge that is in fact zero). The reason is that the dark forces and the visible forces almost talk with each other. The "almost" being very close to zero. Therefore, dark matter will be fully sensitive to the dark forces, and tinily sensitive to electromagnetism by virtue of the small connection between the dark and visible world. More details can be found on this old post of mine (especially the last paragraph).
Do not hesitate to come back to me if you need further pieces of information.