``Alternative $N=(4,0)$ Superstring and $\s$-Models''

We present an alternative $N=(4,0)$ superstring theory, with field content different from that of previously-known $N=(4,0)$ superstring theories. This theory is presented as a non-linear $\s$-model on the coset $SU(n,1) / SU(n) \otimes U(1)$ as the target space-time with torsion, which is coupled to $N=(4,0)$ world-sheet superconformal gravity. Our result indicates that the target space-time for $N=4$ superstring theory does not necessarily have to be a hyper-K\"ahler or quaternionic K\"ahler manifold.