T-duality in arbitrary string backgrounds

T-duality is a poorly understood symmetry of the space-time fields of string theory that interchanges long and short distances. It is best understood in the context of toroidal compactification where, loosely speaking, radii of the torus are inverted. Even in this case, however, conventional techniques permit an understanding of the transformations only in the case where the metric on the torus is endowed with Abelian Killing symmetries. Attempting to apply these techniques to a general metric appears to yield a non-local world-sheet theory that would defy interpretation in terms of space-time fields. However, there is now available a simple but powerful general approach to understanding the symmetry transformations of string theory, which are generated by certain similarity transformations of the stress tensors of the associated conformal field theories. We apply this method to the particular case of T-duality and (i) rederive the known transformations, (ii) prove that the problem of non-locality is illusory, (iii) give an explicit example of the transformation of a metric that lacks Killing symmetries and (iv) derive a simple transformation rule for arbitrary string fields on tori.