Cohomological invariants for G-Galois algebras and self-dual normal   bases
  We define degree two cohomological invariants for G-Galois algebras over fields of characteristic not 2, and use them to give necessary conditions for the existence of a self--dual normal basis. In some cases, we show that these conditions are also sufficient. 
Eva Bayer-Fluckiger, Raman Parimala
math.NT