Effective Field Theory for QCD-like Theories and Constraints on the Two Higgs Doublet Model

University dissertation from Department of Astronomy and Theoretical Physics, Lund University

Abstract: This thesis includes two topics. The first three papers is the major part of this thesis, which is about higher order calculations in the effective field theories of three QCD-like theories. These three QCD-like theories are distinguished by having quarks in a complex, real or pseudo-real representation of gauge group. We wrote their effective field theories in a very similar way so that the calculations can be done using techniques from chiral perturbation theory. We calculated the vacuum-expectation-value, the mass and the decay constant of pseudo-Goldstone bosons up to next-to-next-to leading order (NNLO) in paper I. The various channels of general meson-meson scattering of the three cases were calculated up to NNLO in paper II. In paper III, we calculated the vector, axial-vector, scalar, pseudo-scalar two-point functions and pseudo-scalar decay constant GM up to two-loop level. We also calculated the S parameter for those different QCD-like theories at the TeV scale. The second topic concerns the evolution of Yukawa couplings in general twoHiggs doublet models (2HDM). In paper IV, using the updated experimental and theoretical data, we give the latest constraints on the parameters lambda_ij of the Cheng-Sher ansatz for 2HDM. We show the constraints from the Landau poles and large nondiagonal lambda_ij at a high scalewith various input at electroweak scale for three different cases: models with Z2 symmetry, models with Z2 symmetry breaking but still aligned or diagonal, and models with the Cheng-Sher ansatz.