# To what extent are lepton and quark generations tied in the Standard Model?

The Standard Model of particle physics splits both the leptons and the quarks into three generations, with mass and instability going up from the first to the third generation. These are normally displayed together, on the same rows or columns of the table of fundamental particles:

This makes some sense: each charged lepton is tied to its neutrino in most Feynman vertices it appears in, and the quarks are linked to each other by their charges, if nothing else. However, I can't think of any way in which the SM formally links, say, muons and strange quarks. It's there some explicit link with generation-specific interactions? Or is it just coincidence that there's three rungs in both ladders with increasing mass on both?

• There is nothing, to my knowledge, preventing interchange of any two green columns (doublets) keeping the purple ones unchanged, and vice versa. Historically, they were ordered in mass, from left to right, But for heavily mixed neutrino states that classification is at best confusing. "Generation rank" is not a good quantum number! – Cosmas Zachos Feb 18 '17 at 14:41
• Historically the linkage was the result of Gellmann"s physical intuition. I heard him speak of this linkage right after the discovery of the tau and charmed quark and this led him to predict the b and t wuarks – Lewis Miller Dec 9 '19 at 1:54
• Comtinued; I don't remember him giving any physical reason for the linkage. – Lewis Miller Dec 9 '19 at 1:57

• My point exactly. Because quark mixing is small, people could, and do!, talk about weak and mass eigenstates linked, sloppily. But because neutrino mixing is huge, talking about masses of $\nu_e$, etc is "not even wrong". – Cosmas Zachos Feb 18 '17 at 15:13