Integrable invariant Sobolev metrics on the Abelian extension of the   diffeomorphism group of the circle and two-component generalizations of the   Camassa-Holm equation
  In this note we classify some integrable invariant Sobolev metrics on the Abelian extension of the diffeomorphism group of the circle. We also derive a new two-component generalization of the Camassa-Holm equation. The system obtained appears to be unique bi-Hamiltonian flow on the coadiont obrit of $\Diff_+(S^1)\ltimes C^\infty(S^1)$ generalizes the Camassa-Holm flow on $\Vect(S^1)^*$. 
P.A. Kuzmin