N = 2 heterotic strings revisited

We show that 1 + 1 dimensional vacua of the (0, 2) heterotic string have many properties in common with more recently studied physical systems. The free theory exhibits a symmetric product CFT structure. The single-string Hilbert space splits into sectors labeled by the string winding, w, that contain purely left-moving (for w > 0) and right-moving (for w < 0) excitations. These sectors exhibit infinite-dimensional left and right-moving symmetry algebras, respectively, with central extensions that depend on w. String interactions between left and right-movers appear to lead to a TT¯ deformation of the free theory.