Subclasses of the Conformal Almost Contact Metric Manifolds
  A classification scheme of the conformal almost contact metric manifolds with respect to the covariant derivative of the Lee form is given. The subclasses of one basic class and their exact characterizations by the maximal subgroups of the contact conformal group preserving itself are found. 
Milen J. Hristov, Valentin A. Alexiev
math.DG