New Realisations of W Algebras and W Strings
  We discuss new realisations of $W$ algebras in which the currents are expressed in terms of two arbitrary commuting energy-momentum tensors together with a set of free scalar fields. This contrasts with the previously-known realisations, which involve only one energy-momentum tensor. Since realisations of non-linear algebras are not easy to come by, the fact that this new class exists is of intrinsic interest. We use these new realisations to build the corresponding $W$-string theories and show that they are effectively described by two independent ordinary Virasoro-like strings. 
H. Lu, C.N. Pope, S. Schrans and X.J. Wang