Electric polarization as a nonquantized topological response and boundary Luttinger theorem

We develop a nonperturbative approach to the bulk polarization of crystalline electric insulators in d ≥ 1 dimensions. Formally, we define polarization via the response to background fluxes of both charge and lattice translation symmetries. In this approach, the bulk polarization is related to properties of magnetic monopoles under translation symmetries. Specifically, in 2d the monopole is a source of 2π-flux, and the polarization is determined by the crystal momentum of the 2π-flux. In 3d the polarization is determined by the projective representation of translation symmetries on Dirac monopoles. Our approach also leads to a concrete scheme to calculate polarization in 2d, which in principle can be applied even to strongly interacting systems. For open boundary condition, the bulk polarization leads to an altered ‘boundary’ Luttinger theorem (constraining the Fermi surface of surface states) and also to modified Lieb-Schultz-Mattis theorems on the boundary.