On asymptotic higher analogs of the magnetic helicity invariant in MHD
  A solution of a problem by V.I.Arnol'd about higher analog of the asymptotic Hopf invariant of divergence-free vector fields is presented. A higher invariant of magnetic fields, which is not expressed from the asymptotic linking numbers of magnetic lines is constructed and examples of an asymptotic invariants is constructed. 
Petr M. Akhmet'ev
math.GT math-ph math.MP