In this talk we review some recent applications of generalised symmetries to scattering amplitudes. We start in 4d by describing the connection between spontaneously broken higher-form symmetries and soft theorems for scattering amplitudes of the associated Nambu-Golstone bosons, and show a new soft theorem for theories with a so-called 2-group symmetry. Then, we switch gears and consider non-invertible symmetries in 2d theories. We show that the standard form of the S-matrix is incompatible with the non-invertible symmetry, and derive new S-matrices satisfying a modified crossing symmetry.

Junior Strings is a seminar series where DPhil students present topics of common interest that do not necessarily overlap with their own research area. This is primarily aimed at PhD students and post-docs but everyone is welcome.