Generalized Abelian Gauge Theory & Generalized Global Symmetry

Sammanfattning: We study Cheeger-Simons differential characters in order to define higher form U(1) gauge fields and their Wilson lines. We then go on to define generalized global symmetries. This is a topological formulation of symmetries which has interesting consequences when the charged operators extend through space. Our main source of such charged operators are the generalized Wilson lines. A higher form Noether theorem and a Ward identity are given for transformations of Wilson lines. As examples of quantum field theories with generalized symmetries we cover Sigma models, Maxwell theory and BF-theory. These are examples of Z, U(1) and Zn symmetries respectively. Finally we discuss spontaneous symmetry breaking for higher dimensional symmetries and a Goldstone theorem is provided. These massless Goldstone bosons are shown to have internal structure corresponding to non-zero spin. The photon is identified as the spin one Goldstone boson in QED. Our review of generalized symmetries is more formal than the ones in other papers. This makes various points explicit and leads to general selection rules. Many results of previous papers are reproduced in detail.