Magnetoelectric polarizability in bosonic insulators

1. Systems that break time reversal and inversion symmetries (PT) can have a magnetoelectric response. The magnetoelectric polarizibility of a system of noninteracting fermions in 3 dimensions has been studied in the context of the theta response of topological insulators. We show that an insulator of U(1) charged bosons can also exhibit a magnetoelectric response in the absence of P and T symmetries and compute the corresponding linear response tensor. Such a response may lead to effective axion electrodynamics in U(1) spin liquids coupled with appropriate symmetry breaking orders.