Manifolds with holonomy U*(2m)
  We consider the geometry determined by a torsion-free affine connection whose holonomy lies in the subgroup U*(2m), a real form of GL(2m,C), otherwise denoted by SL(m,H).U(1). We show in particular how examples may be generated from quaternionic K\"ahler or hyperk\"ahler manifolds with a circle action. 
Nigel Hitchin
math.DG