arXiv subjects
Publications and source records attributed to A. Pilaftsis.
We analyze the possibility of universality violation in diagonal leptonic decays of the $Z$ boson, in the context of interfamily "see-saw" models. In a minimal extension of the Standard Model with right-handed neutrino fields, we find that universality-breaking effects increase quadratically with the heavy Majorana neutrino mass and may be observed in the running $LEP$ experiments.
We present an approach to bosonic ($Z^0, W^{\pm}$) as well as fermionic (top-quark) Breit-Wigner propagators which is consistent with gauge invariance arguments. In particular, for the $Z^0$-boson propagator we extend previous analyses and show that the part proportional to $k_μ k_ν/M^2$ must be modified near the resonance. We derive a mass shift which agrees with results obtained elsewhere by different methods. The modified form of a resonant heavy fermion propagator is also given.
In a minimal extension of the Standard Model, in which new neutral fermions have been introduced, we show that the requirement of vanishing anomalies fixes the hypercharges of all fermions uniquely. This naturally leads to electric charge quantization in this minimal scenario which has features similar to the Standard Model: invariance under the gauge group $SU(2)_L\otimes U(1)_Y$, conservation of the total lepton number and masslessness for the ordinary neutrinos. Such minimal models might arise as low-energy realizations of some heterotic superstring models or $SO(10)$ grand unified theories.
We analyze possible lepton-flavor-violating decays of the $Z^0$ particle in a minimal extension of the Standard Model, in which one right-handed neutral field for each family has been introduced. Such rare leptonic decays are induced by Majorana neutrinos at the first electroweak loop level and are generally not suppressed by the ordinary "see-saw" mechanism. In particular, we find that experimental bounds on branching ratios of the order of $10^{-5}-10^{-6}$ attainable at $LEP$ may impose constraints on lepton-flavor-mixing parameters and the masses of the heavy Majorana neutrinos.
Leptonic flavor-changing $H^0$ decays with branching ratios of the order of $10^{-5}-10^{-6}$ may constitute an interesting framework when looking for large $CP$-violating effects. We show that leptonic $CP$~asymmetries of an intermediate $H^0$ boson can be fairly large in natural scenarios of the minimal Standard Model ($SM$) with right-handed neutrinos, at a level that may be probed at future $H^0$~factories.
We calculate the dominant three body Higgs decays, $H \to W^+W^-(Z^0, γ)$ and $H \to t\overline{t}(Z^0,γ,g)$, in the Standard Model. We find that the branching ratios of these decays are of the order of few percent for large Higgs masses. We comment on the behaviour of the partial decay width $Γ(H \to t\overline{b}W^-)$ below the $t\overline{t}$ threshold. Numerical results of the following three body top decays, $t \to W^+b(γ,g,Z^0)$ and $t \to W^+bH$, are also given. We discuss the feasibility of observing these Higgs and top decays at future high energy colliders.
We formulate the conditions under which a purely bosonic theory (without fermions) containing neutral spin-0 particles and vector (gauge) bosons violates the CP-symmetry through the presence of CP-even and CP-odd operators in the Lagrangian. This is done without reference to explicitly CP-violating scalar sector of extended standard models (SM) with two or more Higgs doublets. The Lagrangian expressed in the mass basis of the spin-0 fields can, however, in certain cirumstances be identified with a part of the CP-violating SM with two Higgs doublets. It is instructive to consider the manifestation of CP-violation in the mass basis since this leads directly to suggestions of genuine CP-signals.
We study $CP$ violation in the process $e^+e^- \to t\bar{t} ν\barν$ at an $e^+e^-$-TeV collider. As the source of $CP$ violation we assume a two-Higgs doublet model with an explicitly $CP$-noninvariant Higgs potential. Sizeable $CP$-odd observables originating from the subprocess reaction, $W^+W^- \to t\bar{t}$, may arise as a result of finite width effects of the neutral Higgs particles. $CPT$ constraints due to final (initial) state interactions are also taken into account. Numerical estimates of the $CP$ asymmetry are given.