Variational approach to thermal masses in compactified models

We investigate by means of a variational approach the eective potential of a 5D U(1) scalar model atnite temperature and compactied on S 1 and S 1 =Z2 as well as the corresponding 4D model obtained through a trivial dimensional reduction. We are particularly interested in the behavior of the thermal masses of the scalareld with respect to the Wilson line phase and the results obtained are compared with those coming from a one-loop eective potential calculation. We also explore the nature of the phase transition.