M. A. Perez

Analysis of t-b-W and t-t-Z couplings from CLEO and LEP/SLC data

Abstract We update the constraints on anomalous dimension four t - b - W and t - t - Z couplings by using CLEO b → sγ and LEP/SLC precision Z -pole data. It is found that the data imposes very stringent bounds on them. Moreover, the 2 σ pull from SM predictions of A LR (hadrons), A b and A FB ( b ) have little chance of being explained by the strongly constrained anomalous couplings.

Constraints on top-quark flavor changing neutral couplings from electroweak precision measurements

We study the one-loop contributions of the effective flavor changing neutral couplings (FCNC) tcZ and tcH on the electroweak precision observables Gamma_Z, R_c, R_b, R_l, A_c and A^FB_c. Using the known experimental limits on these observables, we may place 95% CL bounds on these FCNC couplings which in turn translate into the following limits for the branching ratios: BR(t -> cZ) cH) < (0.09 - 2.9) 10^-3 for 114 < m_H < 170 GeV.

Testing flavor-changing neutral currents in the rare top quark decayst→cViVj

We discuss the Flavor-Changing Neutral Current (FCNC) decays of the top quark t -> c Vi Vj (Vi=gamma, Z, g) in the framework of the Standard Model (SM) and in a two-higgs doublet model (2HDM) with tree-level FCNC couplings. While in the SM the expected branching ratios are extremelly small, in the 2HDM they may be sizable, of order 10^(-5) - 10^(-5), and thus accesible at the CERN LHC. We conclude with the interesting observation that the FCNC decay modes may not be equally suppressed as their corresponding decays t ->c Vi in this 2HDM.

Implications of b → sγ on the anomalous electromagnetic couplings of gauge bosons and quarks

Abstract We reexamine the possible deviations from the standard model on the decay b → sγ within the context of an effective Lagrangian approach. We consider dimension-6 operators which are SU(2) L ×U(1) Y gauge invariant and contribute to this decay mode at tree-and one-loop level. Using the recent results of the CLEO Collaboration on radiative B decays, we get constraints on the anomalous electromagnetic couplings of the W boson and the quarks t , c , u . We get an improved constraints of the anomalous magnetic moment of the quark t as compared to that obtained with only U(1) EM gauge-invariant dimension-6 operators. As a byproduct, we obtain also a bound on the decay width of t → cγ .

Impact of a four-zero Yukawa texture on h → γγ and γZ in the framework of the Two Higgs Doublet Model Type III

A bstractWe study the substantial enhancement, with respect to the corresponding Standard Model rates, that can be obtained for the branching ratios of the decay channels h → γγ and h → γZ within the framework of the Two Higgs Doublet Model Type III, assuming a four-zero Yukawa texture and a general Higgs potential. We show that these processes are very sensitive to the flavor pattern entering the Yukawa texture and to the triple coupling structure of the Higgs potential, both of which impact onto the aforementioned decays. We can accommodate the parameters of the model in such a way to obtain the h → γγ rates reported by the Large Hadron Collider and at the same time we get a h → γZ fraction much larger than in the Standard Model, indeed within experimental reach. We present some scenarios where this phenomenology is realized for spectrum configurations that are consistent with current constraints. We also discuss the possibility of obtaining a light charged Higgs boson compatible with all such measurements, thereby serving the purpose of providing a hallmark signal of the scenario considered.

Constraints on νi → νjγ from μ → eγ, τ → μγ, eγ

Abstract Using the effective Lagrangian approach, we obtain bounds on the lepton-number-nonconserving decays ν μ → ν e γ , ν τ → ν μ γ , ν e γ from the known experimental constraints on μ → eγ and τ → μγ , eγ . We get a bound on the transition magnetic moment of the muon neutrino κ μe ⩽ 1 × 10 −11 for m νμ ⩽ 270 keV, which improves the bound obtained from astrophysical considerations. Our results also lead to bounds on the transition magnetic moments of the τ neutrino.

Bounding the magnetic and electric dipole moments of

We obtain bounds on the anomalous magnetic and electric dipole moments of the tau-neutrino through the reaction

\nu_{tau}

e^{+}e^{-}\to \nu \bar \nu \gamma

from the process

at the

e^{+} e^{-} \to \nu \bar{\nu} \gamma

Z_1