The challenge of non-hermitian structures in physics
  We present a brief review of physical problems leading to indefinite Hilbert spaces and non-hermitian Hamiltonians. With the exception of pseudo-Riemannian manifolds in GR, the problem of a consistent physical interpretation of these structures still waits to be faced.   In print in Rev. Mex. Fis. 
A. Ramirez and B. Mielnik