Hyperkähler, bi-hypercomplex, generalized hyperkähler structures and T-duality

Abstract

We exploit the doubled formalism to study comprehensive relations among T-duality, complex and bi-hermitian structures (J+,J−) in two-dimensional N=(2,2) sigma models with/without twisted chiral multiplets. The bi-hermitian structures (J+,J−) embedded in generalized Kähler structures (J+,J−) are organized into the algebra of the tri-complex numbers. We write down an analogue of the Buscher rule by which the T-duality transformation of the bi-hermitian and Kähler structures are apparent. We also study the bi-hypercomplex and hyperkähler cases in N=(4,4) theories. They are expressed, as a T-duality covariant fashion, in the generalized hyperkähler structures and form the split-bi-quaternion algebras. As a concrete example, we show the explicit T-duality relation between the hyperkähler structures of the KK-monopole (Taub-NUT space) and the bi-hypercomplex structures of the H-monopole (smeared NS5-brane). Utilizing this result, we comment on a T-duality relation for the worldsheet instantons in these geometries.