On the number of eigenvalues of Schr\"odinger operators with complex   potentials
  We study the eigenvalues of Schr\"odinger operators with complex potentials in odd space dimensions. We obtain bounds on the total number of eigenvalues in the case where $V$ decays exponentially at infinity. 
Rupert L. Frank, Ari Laptev, Oleg Safronov
math.SP math-ph math.MP