Gravitons increase the speed at which a charge sphere spins and increase its mass. So an electron has a smaller mass than a proton because its spins more slowly. Because the proton has 1835 x mass of electron and because the electron spins at 10 ^ 14 metres per second - to give the observed magnetic moment- this means,bearing in mind (1 – v^2 / vfast^2)^ 1/2 , that the proton spins at 10 ^ 17 metres per second – at least !! The spin of a charge sphere is quantised. Gravitons and photons are massless because they don’t have spinning charges. It is my belief that they consist of non-spinning quarks.