Lecture, four hours. Requisites: courses 221A, 221B, 221C, 230A, 230B (230A, 230B may be taken concurrently). Modern theories of elementary particle physics beginning with symmetry principles and conserved quantities, classic V-A theory of weak interactions, gauge field theories (Abelian and non-Abelian), spontaneous symmetry breaking, SU(2) x U(1) electroweak interactions of leptons, quarks, Ws, Zo and y, quark theory of hadrons and quantum chromodynamics. S/U or letter grading.