Gauge dependence ambiguity and chemical potential in thermal U(1) theory
  In this letter we explore the dependence on the gauge fixing condition of several quantities in the U(1) Higgs model at finite temperature and chemical potential. We compute the effective potential at the one loop level, using a gauge fixing condition that depends on $\mu$ and which allows to decouple the contributions of the different fields in the model. In this way we get the mass spectrum and the characterization of the phase transition, pointing out in each case how these quantities depend on the gauge fixing parameter $\xi$. When $\mu$ vanishes, we agree with previous results if $\xi=0$. The gauge dependence problem is also analyzed from the perspective of the Nielsen identities. 
M. Loewe, S. Mendizabal and R.A. Santos