Dimensional reduction of the Two-Higgs Doublet Model with a softly broken Z2 symmetry at one-loop
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- Institutt for fysikk 
In the collaboration between NTNU, the University of Stavanger, and the University of Helsinki we pursue a satisfactory answer to the problem of baryogenesis, i.e. the origin of the asymmetry in the amount of baryons and antibaryons in the universe. Baryogenesis at the electroweak phase transition cannot be explained by the Standard Model as the phase transition is a crossover, not strongly first order as required. In addition, the amount of CP violation in the Standard Model is insufficient. Therefore, we investigate extensions of the Standard Model to find a viable candidate for explaining baryogenesis. Using the imaginary-time formalism for quantum field theories at finite temperature, we have applied the method of dimensional reduction to the Two-Higgs Doublet Model with a softly broken $Z_2$ symmetry. An effective three-dimensional Euclidean bosonic theory was constructed by integrating out all non-zero Matsubara modes. The parameters of the effective three-dimensional theory were determined in terms of the parameters of the original four-dimensional theory, by matching the correlators at long distances. The effective potential was used to find the scalar correlators. The discussion was extended to the $N$-Higgs Doublet Model, where CP violation is only present in the mass-mixing terms. The results obtained here will be used in a numerical simulation of the electroweak phase transition in a future paper.