Spacetime Scale-Invariance and the Super p-Brane
  We generalize to p-dimensional extended objects and type II superstrings a recently proposed Green-Schwarz type I superstring action in which the tension $T$ emerges as an integration constant of the equations of motion. The action is spacetime scale-invariant but its equations of motion are equivalent to those of the standard super p-brane for $T\ne 0$ and the null super p-brane for $T=0$. We also show that for $p=1$ the action can be written in ``Born-Infeld'' form. 
E. Bergshoeff, L.A.J London and P.K. Townsend