Euclidean Supersymmetry, Twisting and Topological Sigma Models
  We discuss two dimensional N-extended supersymmetry in Euclidean signature and its R-symmetry. For N=2, the R-symmetry is SO(2)\times SO(1,1), so that only an A-twist is possible. To formulate a B-twist, or to construct Euclidean N=2 models with H-flux so that the target geometry is generalised Kahler, it is necessary to work with a complexification of the sigma models. These issues are related to the obstructions to the existence of non-trivial twisted chiral superfields in Euclidean superspace. 
C.M. Hull, U. Lindstrom, L. Melo dos Santos, R. von Unge, and M.   Zabzine