Symmetries and Phase Structure of the Layered Sine-Gordon Model
  The phase structure of the layered sine-Gordon (LSG) model is investigated in terms of symmetry considerations by means of a differential renormalization group (RG) method, within the local potential approximation. The RG analysis of the general N-layer model provides us with the possibility to consider the dependence of the vortex dynamics on the number of layers. The Lagrangians are distinguished according to the number of zero eigenvalues of their mass matrices. The number of layers is found to be decisive with respect to the phase structure of the N-layer models, with neighbouring layers being coupled by terms quadratic in the field variables. It is shown that the LSG model with N layers undergoes a Kosterlitz--Thouless type phase transition at the critical value of the parameter \beta^2_{c} = 8 N \pi. In the limit of infinitely many layers the LSG model can be considered as the discretized version of the three-dimensional sine-Gordon model which has been shown to have a single phase within the local potential approximation. The infinite critical value of the parameter \beta_c^2 for the LSG model in the continuum limit (N -> \infty) is consistent with the latter observation. 
I. Nandori