The Dark Quark
I postulate that a “dark quark” exists. It is almost identical to an up quark except that the up quark has a charge of +2/3 and the dark quark has no charge. I postulate that all the standard model elementary particles are made of fundamental particles which I am naming “knucks”. Both the up quark and the dark quark have a triangular “ring” composed of two positive and one negative knucks. Each has a fourth knuck oscillating back and forth through the center of the triangular ring of two positive and one negative knucks. In the up quark the fourth knuck is positive and the charge on the up quark is +2/3. In the dark quark the fourth knuck is negative and the charge on the dark quark is zero. The energy of the two configurations should be almost identical since the oscillation of the fourth knuck is probably due to magnetic attraction and probably little effected by the electrical charge differences.
The anti-dark quark is similar except it has a positive fourth knuck oscillating back and forth through the center of a triangular ring of one positive and two negative knucks.
The dark quark has mass and it may move rapidly or slowly but its movement is altered only by gravity since it has no net electrical or magnetic charge. Its mass is essentially the same as an up quark – about 2.2 MeV/c^2 – which is about five times the mass of an electron and like the electron it may have a very long lifetime. It is unlikely that the dark quark will interact with other matter.
Whatever process originally formed the up quarks in the universe probably also formed dark quarks and they may be currently formed in interactions involving W+ and W- bosons along with neutrinos.