T-duality and HKT manifolds

We examine conformal rescaling and T-duality in the context of four-dimensional HKT geometries. The closure of the torsion forces the conformal factor to satisfy a modified harmonic equation. Because of this equation the conformal factors form non-commutative groups acting on the HKT geometries. Using conformal rescalings and T-duality transformations we generate from flat space new families of HKT geometries with tri-holomorphic Killing vectors. We also find ultraviolet-finite (4,0) supersymmetric sigma models which are not conformally invariant.