Matt McIrvin on Nostr: ...Right. Conventionally we think of a pion as a quark-antiquark bound state, and a ...

...Right.

Conventionally we think of a pion as a quark-antiquark bound state, and a proton or neutron as a bound state of three quarks. But naively, from that picture, you'd expect a pion to have about 2/3 of the mass of a proton, and they're much lighter than that, more like 1/7 the mass of a proton.

The sigma-model picture is a rough way of picturing how that can be.