Variational approach to thermal masses in compactified models

We investigate by means of a variational approach the effective potential of a 5 D U(1) scalar model at finite temperature and compactified on S 1 and S 1 / Z 2 as well as the corresponding 4 D model obtained through a trivial dimensional reduction. We are particularly interested in the behavior of the thermal masses of the scalar field with respect to the Wilson line phase and the results obtained are compared with those coming from a one-loop effective potential calculation. We also explore the nature of the phase transition