Stability and Symmetry Breaking in the General Two-Higgs-Doublet Model
  A method is presented for the analysis of the scalar potential in the general Two-Higgs-Doublet Model. This allows us to give the conditions for the stability of the potential and for electroweak symmetry breaking in this model in a very concise way. These results are then applied to two different Higgs potentials in the literature, namely the MSSM and the Two-Higgs-Doublet potential proposed by Gunion at al. All known results for these models follow easily as special cases from the general results. In particular, in the potential of Gunion et al. we can clarify some interesting aspects of the model with the help of the proposed method. 
M. Maniatis, A. von Manteuffel, O. Nachtmann, F. Nagel