Dimensionless Coupling of Superstrings to Supersymmetric Gauge Theories   and Scale Invariant Superstring Actions
  We construct new superstring actions which are distinguished from standard superstrings by being space-time scale invariant. Like standard superstrings, they are also reparametrization invariant, space-time supersymmetric, and invariant under local scale transformations of the world sheet. We discuss scenarios in which these actions could play a significant role, in particular one which involves their coupling to supersymmetric gauge theories. 
M. Awada and F. Mansouri