Search for Single Vectorlike Quarks in p(p)over-bar Collisions at root s=1.96 TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Search for the Standard Model Higgs Boson in the H -> WW -> lvq '(q)over-bar Decay Channel

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Measurement of the t-Channel Single Top Quark Production Cross Section in pp Collisions at root s=7 TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Z '(B-L) phenomenology at the LHC

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Neutrino masses and the scalar sector of a B-L extension of the standard model

We consider an electroweak model based on the gauge symmetry SU(2)(L) circle times U(1)(Y') circle times U(1)(B-L) which has right-handed neutrinos with different exotic B - L quantum numbers. Because of this particular feature we are able to write Yukawa terms, and right-handed neutrino mass terms, with scalar fields that can develop vacuum expectation values belonging to different energy scales. We make a detailed study of the scalar and the Yukawa neutrino sectors to show that this model is compatible with the observed solar and atmospheric neutrino mass scales and the tribimaximal mixing matrix. We also show that there are dark matter candidates if a Z(2) symmetry is included.

Measurement of the weak mixing angle with the Drell-Yan process in proton-proton collisions at the LHC

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Is the LHC observing the pseudoscalar state of a two-Higgs-doublet model?

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

A descoberta das correntes neutras das interações fracas

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

NEUTRINOLESS DOUBLE-BETA DECAY IN AN SU(3)(L)CIRCLE-TIMES-U(1)(N) MODEL

We consider a model for the electroweak interactions with the SU(3)(L) circle times U(1)(N) gauge symmetry. We show that the conservation of the quantum number F = L+B forbids the appearance of massive neutrinos and the neutrinoless double-beta decay (beta beta)(0 nu). Explicit or/and spontaneous breaking of F implies that the neutrinos have an arbitrary mass. In addition the (beta beta)(0 nu) decay also has some channels that do not depend explicitly on the neutrino mass.

HEAVY CHARGED LEPTONS IN AN SU(3)L-CIRCLE-TIMES-U(1)N MODEL

We consider an SU(3)L x U(1)N model for the electroweak interactions which includes extra charged leptons which do not mix with the known leptons. These new leptons couple to Z0 only through vector currents. We consider constraints on the mass of one of these leptons coming from the Z0 width and from the muon (g - 2) factor. The last one is less restrictive than the former.

Limits on anomalous top couplings from Z pole physics

We obtain constraints on possible anomalous interactions of the top quark with the electroweak vector bosons arising from the precision measurements at the Z pole. In the framework of SU(2)L ⊕ U(1)Y chiral Lagrangians, we examine all effective CP-conserving operators of dimension five which induce fermionic currents involving the top quark. We constrain the magnitudes of these anomalous interactions by evaluating their one-loop contributions to the Z pole physics. Our analysis shows that the operators that contribute to the LEP observables get bounds close to the theoretical expectation for their anomalous couplings. We also show that those which break the SU(2)C custodial symmetry are more strongly bounded. © 1997 Elsevier Science B.V.

Left-right asymmetries in polarized lepton-lepton scattering

Several parity-violating left-right asymmetries in Miller electron-electron and muon-muon scattering are considered in the context of the electroweak standard model at the tree level in fixed target and collider experiments. We show that in colliders the asymmetry with only one of the beams polarized is large enough to compensate the smaller cross section at high energies. We also show that these asymmetries are very sensitive to a doubly charged vector bilepton resonance but they are insensitive to scalar ones.

Scalar resonances in leptophilic multi-Higgs-boson models

We show that the Higgs resonance can be amplified in a 3-3-1 model with a multi-Higgs-boson leptophilic scalar sector. This would allow the observation of the Higgs particle in muon colliders even for Higgs boson masses considerably higher than the ones expected to be seen in the electroweak standard model framework. ©1999 The American Physical Society.

Remark on the vectorlike nature of electromagnetism and electric charge quantization

In this work we study the structure of electromagnetic interactions and electric charge quantization in gauge theories of electroweak interactions based on semisimple groups. We show that in the standard model of electroweak interactions the structure of electromagnetic interactions is strongly correlated to the quantization pattern of electric charges. We examine these two questions also in all possible chiral bilepton gauge models of electroweak interactions. In all, we can explain the vectorlike nature of electromagnetic interactions and electric charge quantization together demanding nonvanishing fermion masses and anomaly cancellations. ©1999 The American Physical Society.

Neutrinoless double beta decay with and without Majoron-like boson emission in a 3-3-1 model

We consider the contributions to the neutrinoless double beta decays in a SU(3)L⊗U(1)N electroweak model. We show that for a range of parameters in the model there are diagrams involving vector-vector-scalar and trilinear scalar couplings which can be potentially as contributing as the light massive Majorana neutrino exchange one. We use these contributions to obtain constraints upon some mass scales of the model, such as the masses of the new charged vector and scalar bosons. We also consider briefly the decay in which, in addition to the two electrons, a Majoron-like boson is emitted. ©2001 The American Physical Society.