Abstract

We build unitary representations of the BMS algebra and its higher-spin extensions in three dimensions, using induced representations as a guide. Our prescription naturally emerges from an ultrarelativistic limit of highest-weight representations of Virasoro and W algebras, which is to be contrasted with nonrelativistic limits that typically give nonunitary representations. To support this dichotomy, we also point out that the ultrarelativistic and nonrelativistic limits of generic W algebras differ in the structure of their nonlinear terms.