Infinitely many rigid symmetries of kappa-invariant D-string actions

We show that each rigid symmetry of a D-string action is contained in a family of infinitely many symmetries. In particular, kappa-invariant D-string actions have infinitely many supersymmetries. The result is not restricted to standard D-string actions, but holds for any two-dimensional action depending on an abelian world-sheet gauge field only via the field strength. It applies thus also to manifestly $SL(2,Z)$ covariant D-string actions. Furthermore, it extends analogously to $d$-dimensional actions with $(d-1)$-form gauge potentials, such as brane actions with dynamical tension.