I've been trying to learn more about the standard model. Leonard Susskind's lectures have been very helpful for SR, GR and QM. His lectures about the standard model are interesting, I learned a lot, no question. But he doesn't really cover in any depth the mathematical side of it. He mentions the various symmetry groups, but that's about it. What book(s) about the standard model can you suggest that don't try to be easy on the mathematics side of the standard model?