Embeddings of the Virasoro algebra and black hole entropy
  We consider embeddings of the Virasoro algebra into other Virasoro algebras with different central charges. A Virasoro algebra with central charge c (assumed to be a positive integer) and zero mode operator L_0 can be embedded into another Virasoro algebra with central charge one and zero mode operator c L_0. We point out that this provides a new route to investigate the black hole entropy problem in 2+1 dimensions. 
Maximo Banados