  Owing to Lorentz invariance, the leading terms in the effective action
describing the low-energy dynamics of flux tubes in a confining gauge theory
are universal. Besides the terms corresponding to the Nambu-Goto action,
Lorentz invariance also allows terms describing a "rigid string", proposed long
ago by Kleinert and Polyakov as a model for confinement in a dual
superconductor scenario. In this contribution we discuss some of the
non-trivial properties of this type of string and evaluate analytically the
corrections to the interquark potential induced by extrinsic curvature terms
appearing in the rigid string action.
