Between generations, particles differ by their flavour quantum number and mass, but their electric and strong interactions are identical.
There are functions used to generalize terms for introduction in a new quark that is an isosinglet and is responsible for generating Flavour-Changing-Neutral-Currents' (FCNC) at tree level in the electroweak sectors.
[6][7] Furthermore, a fourth generation with a 'light' neutrino (one with a mass less than about 45 GeV/c2) has been ruled out by measurements of the decay widths of the Z boson at CERN's Large Electron–Positron Collider (LEP).
[8] Nonetheless, searches at high-energy colliders for particles from a fourth generation continue, but as yet no evidence has been observed.
String theory provides a cause for multiple generations, but the particular number depends on the details of the compactification of the D-brane intersections.
Additionally, E8 grand unified theories in 10 dimensions compactified on certain orbifolds down to 4 D naturally contain 3 generations of matter.