Abstract:Two program packages are presented for evaluating one-loop amplitudes. They can work either in dimensional regularization or in constrained differential renormalization. The latter method is found at the one-loop level to be equivalent to regularization by dimensional reduction.

We obtain constraints on the mixing of vector-like quarks coupling predominantly to the third generation. We consider all (seven) relevant types of vectorlike quarks, individually. The constraints are derived from oblique corrections and Z → bb measurements at LEP and SLC. We investigate the implications of these constraints on LHC phenomenology, concerning the decays of the heavy quarks and their single production. We also explore indirect effects of heavy quark mixing in top and bottom couplings. A remarkable effect is the possibility of explaining the anomalous forward-backward asymmetry in Z → bb at LEP with a hypercharge −5/6 doublet. We also study the impact of the new quarks on single Higgs production at the LHC and Higgs decay.

We obtain limits on generic vector-like leptons at the TeV scale from electroweak precision tests. These limits are complementary to the ones obtained from lepton flavour violating processes. In general, the quality of the global electroweak fit is comparable to the one for the Standard Model. In the case of an extra neutrino singlet mixing with the muon or electron, the global fit allows for a relatively large Higgs mass (M H 260 GeV at 90 % C.L.), thus relaxing the tension between the direct LEP limit and the Standard Model fit. *

Abstract:We compute all the tree-level contributions to the Wilson coefficients of the dimension-six Standard-Model effective theory in ultraviolet completions with general scalar, spinor and vector field content and arbitrary interactions. No assumption about the renormalizability of the high-energy theory is made. This provides a complete ultraviolet/infrared dictionary at the classical level, which can be used to study the low-energy implications of any model of interest, and also to look for explicit completions consistent with low-energy data.

Radiative corrections arising from the axial coupling of charged fermions to a constant vector b µ can induce a Lorentz-and CPT-violating Chern-Simons term in the QED action. We calculate the exact one-loop correction to this term keeping the full b µ dependence, and show that in the physically interesting cases it coincides with the lowest-order result. The effect of regularization and renormalization and the implications of the result are briefly discussed.