Signals of CP Violation in Distributions of Top-Quark Decay Products at Linear Colliders

Angular and energy distributions for leptons and bottom quarks in the process e+e- --> t tbar --> l/b ... have been calculated assuming the most general top-quark couplings. The double distributions depend both on modification of the top-quark production and tbW decay vertices. However, the leptonic angular distribution turned out to be insensitive to non-standard parts of tbW vertex. The method of optimal observables have been used to estimate sensitivity of future measurements at linear e+e- collidersComment: 7 pages, LaTex, 1 figure, talk given at PASCOS '99, Lake Tahoe, California, December 10-16, 1999, typos in the reference list correcte

Extra Dimension Kaluza-Klein Excitations and Electroweak Symmetry Breaking

We review the possibilities that the Kaluza-Klein excitations of graviton states induce electroweak symmetry breaking and that electroweak symmetry breaking could have a large impact on KK phenomenology.Comment: 6 pages, no figure

Measuring CP violation in Two-Higgs-Doublet models in light of the LHC Higgs data

In Two-Higgs-Doublet models, the conditions for CP violation can be expressed in terms of invariants under U(2) rotations among the two SU(2) Higgs doublet fields. In order to design a strategy for measuring the invariants we express them in terms of observables, i.e., masses and couplings of scalar bosons. We find amplitudes directly sensitive to the invariants. Observation of the Standard-Model-like Higgs boson at the LHC severely constrains the models. In particular, in the model with Z_2 symmetry imposed on dimension-4 terms (in order to eliminate tree-level flavour-changing neutral currents), CP violation is strongly suppressed. On the other hand, the most general Two-Higgs-Doublet model (without Z_2 symmetry) would still allow for CP violation to be present in the model, without being in conflict with the LHC data. Consequently, also flavour-changing neutral currents would in general be expected. We briefly sketch a strategy for measuring the remaining CP violation.Comment: 26 pages, 7 figures. Version published in JHE

Testing the presence of CP violation in the 2HDM

We review CP properties of the Two-Higgs-Doublet model. In particular, we show that spontaneous CP violation occurs in the parameter space on the border between regions allowing explicit CP violation and those where there is another minimum, deeper than the one corresponding to v=246 GeV. We discuss weak-basis invariants which describe CP violation and express them through measurable quantities like coupling constants and masses. Also, we discuss how CP violation is constrained by the LHC Higgs data. Finally, we identify effective operators that could be adopted to measure CP-invariants.Comment: 9 pages, Proceedings of the Corfu Summer Institute 2014 "School and Workshops on Elementary Particle Physics and Gravity", 3-21 September 2014 Corfu, Greece. v2: References adde

Diagnosing CP properties of the 2HDM

We have investigated a Two-Higgs-Doublet Model (2HDM), focusing on CP violation. Various scenarios with spontaneous and explicit breaking of CP have been considered. Some features of CP violation related to a choice of the basis for the two Higgs doublets have been discussed and clarified. Regions in the physical parameter space corresponding to spontaneous and explicit CP violation have been located and discussed. The possibility to determine parameters of the scalar potential with no reference to Yukawa couplings has been considered and an unavoidable ambiguity has been found. The issue of disentangling spontaneous and explicit CP violation has been investigated.Comment: 32 pages, 5 figures. Minor changes. Version to appear in JHE