  We find a mapping of the layered sine-Gordon model to an equivalent gas of
topological excitations and determine the long-range interaction potentials of
the topological defects. This enables us to make a detailed comparison to the
so-called layered vortex gas, which can be obtained from the layered
Ginzburg-Landau model. The layered sine-Gordon model has been proposed in the
literature as a candidate field-theoretical model for Josephson-coupled
high-T_c superconductors, and the implications of our analysis for the
applicability of the layered sine-Gordon model to high-T_c superconductors are
discussed. We are led to the conjecture that the layered sine--Gordon and the
layered vortex gas models belong to different universality classes. The
determination of the critical temperature of the layered sine-Gordon model is
based on a renormalization-group analysis.
