Supersymmetric E8(+8)/SO(16) sigma-model coupled to N=1 supergravity in three dimensions

A three-dimensional simple N=1 supergravity theory with a supersymmetric sigma-model on the coset E8(+8)/SO(16) is constructed. Both bosons and fermions in the matter multiplets are in the spinorial 128-representation of SO(16) with the same chirality. Due to their common chirality, this model cannot be obtained from the maximal N=16 supergravity. By introducing an independent vector multiplet, we can also gauge an arbitrary subgroup of SO(16) together with a Chern–Simons term. Similar N=1 supersymmetric σ-models coupled to supergravity are also constructed for the cosets F4(−20)/SO(9) and SO(8,n)/SO(8)×SO(n).