  New qualitative picture of vortex length-scale dependence has been found in
recent electrical transport measurements performed on strongly anisotropic
BSCCO single crystals in zero magnetic field. This indicates the need for a
better description of the 3D/2D crossover in vortex dimensionality. The
vortex-dominated properties of high transition temperature superconductors with
extremely high anisotropy (layered systems) are reasonably well described in
the framework of the layered XY model which can be mapped onto the layered
sine-Gordon model. For the latter we derive an exact renormalization group (RG)
equation using Wegner's and Houghton's approach in the local potential
approximation. The agreement of the UV scaling laws find by us by linearizing
the RG equations with those obtained previously in the literature in the dilute
gas approximation makes the improvement appearant which can be achieved by
solving our RG equations numerically.
