Actions for the Bosonic String with the Curved Worldsheet

At first we introduce an action for the string, which leads to a worldsheet that always is curved. For this action we study the Poincar'e symmetry and the associated conserved currents. Then, a generalization of the above action, which contains an arbitrary function of the two-dimensional scalar curvature, will be introduced. An extra scalar field enables us to modify these actions to Weyl invariant models.