Spin Inversion Symmetry
Spin Inversion Symmetry (SIS) is currently a conjecture.
It says that every elementary particle in the Standard Model (except for the Higgs) of spin s has a dual particle of spin 1/s. Clearly, that demands spin 2 elementary particles, so gravity appears naturally.
Applying SIS to the 3 neutrinos (electron neutrino, muon neutrino, tau neutrino), and assuming charge is conserved, we get 3 neutral spin-2 bosons.
Applying SIS to the 3 leptons (electron, muon, tau), and assuming charge is conserved, we get 3 charged spin-2 bosons.
Applying SIS to the 6 quarks, and assuming charge is conserved, we get 6 charged spin-2 bosons.
That's a total of 12 spin-2 bosons, 9 charged and 3 neutral.
The photon is interesting. It's spin-1 so the photon is its own dual. The same is true for the W and Z bosons that mediate the weak force, and also for the gluon that mediates the color force.
SIS is still a conjecture. But if true the implications are very deep. It says the universe is awash in spin-2 bosons and the particles we currently know in the Standard Model are only a fraction of the particles out there.
Content written and posted by Ken Abbott firstname.lastname@example.org