Gauge dependence of effective potential and self-consistent dimensional reduction

The gauge dependence of the effective potential determining the Kaluza-Klein radius self-consistently is contrasted to that belonging to a gauge theory with spontaneous symmetry breaking at finite temperature. Formally the two quantities are computed in the same way and obey the same Ward identities, but a gauge-independent approximation scheme is possible only in the latter case because of the coupling between the Goldstone field and the longitudinal vector field. The connection to the Ward identities of the two theories is also obtained.