Cotton Blend Gravity $pp$ Waves
  We study conformal gravity in d=2+1, where the Cotton tensor is equated to a--necessarily traceless--matter stress tensor, for us that of the improved scalar field. We first solve this system exactly in the $pp$ wave regime, then show it to be equivalent to topologically massive gravity. 
S. Deser (Brandeis), R. Jackiw (MIT), S.-Y. Pi (Boston University)