Differentiable conjugacy for groups of area preserving circle   diffeomorphisms
  We study groups of circle diffeomorphisms whose action on the cylinder $\mathcal C=\mathbb S^1\times \mathbb S^1\setminus \Delta$ preserves a volume form. We first show that such a group is topologically conjugate to a subgroup of $\rm{PSL}(2,\mathbb R)$, then discuss the existence of a differentiable conjugacy. 
Daniel Monclair
math.DS math.DG math.GT