arXiv subjects

J. J. Toscano

Publications and source records attributed to J. J. Toscano.

89 records · Page 5Linked to original sources

arXiv2003

$H^+ W^- Z$ contribution to the static quantities of the W boson in the context of Higgs-triplet theories

We calculate the one--loop contribution from the $H^+ W^- Z$ coupling to the static electromagnetic properties of the W boson. Although this coupling is absent at the tree--level in all Higgs--doublet models, it can be induced at this order in models including Higgs--triplet representations. It is found that the $H^+ W^- Z$ contribution can be as important as those arising from other couplings including Higgs bosons, such as the standard model coupling WWH or the two--Higgs--doublet model couplings $H^+ W^- ϕ^0$ and $W W ϕ^0$, with $ϕ^0=h$, $H$ and $A$.

hep-ph↗

arXiv2003

New physics effects in rare Z decays

Virtual effects induced by new physics in rare Z decays are reviewed. Since the expected sensitivity of the giga-Z linear collider is of the order of $10^{-8}$, we emphasize the importance of any new physics effect that gives a prediction above this limit. It is also pointed out that an improvement on the known experimental constraints on rare Z decays will provide us with a critical test of the validity of the standard model at the loop level.

hep-ph↗

arXiv2002

Rare decay Z --> neutrino antineutrino photon photon via quartic gauge boson couplings

We present a detailed calculation of the rare decay Z --> neutrino antineutrino photon photon via the quartic neutral gauge boson coupling Z-Z-photon-photon in the framework of the effective Lagrangian approach. The current experimental bound on this decay mode is then used to constrain the coefficients of this coupling. It is found that the bounds obtained in this way, of the order of $10^{-1}$, are weaker than the ones obtained from the analysis of triple-boson production at LEP-2

hep-ph↗

arXiv2002

Effective Lagrangian description of the lepton flavor violating decays Z-->li lj

A comprehensive analysis of the lepton flavor violating (LFV) decays Z-->li lj is presented within the effective Lagrangian approach. Both the decoupling and nondecoupling scenarios are explored. The experimental constraints from li --> lj lk \bar{lk} and li -->lj gamma as well as some relationships arising from the gauge invariance of the effective Lagrangian are used to put constraints on Z-->li lj. It is found that while current experimental data impose very strong constraints on Z-->mu e, the channel Z --> tau mu (e)still may be at the reach of the planned TESLA collider.

hep-ph↗

arXiv2001

Bilepton gauge boson contribution to the static electromagnetic properties of the W boson in the minimal 331 model

We present a complete calculation of the singly and doubly charged gauge bosons (bileptons) contribution to the static properties of the W boson in the framework of the minimal 331 model, which accommodates the bileptons in an SU_L(2) doublet. A nonlinear R_ξgauge is used and a slightly modified version of the Passarino-Veltman reduction scheme is employed as in this case the Gram determinant vanishes. It is found that the bilepton contribution is of the same order of magnitude as those arising from other weakly coupled renormalizable theories, like the two-Higgs doublet model and supersymmetry. The heavy mass limit is explored and the nontrivial decoupling properties of bileptons are discussed. Although there is a close resemblance with the contribution of an SU_L(2) fermion doublet, in the case of the bilepton doublet the decoupling theorem does remain valid. As a by-product, we present a detailed study of the trilinear and the quartic vertices involving the bileptons and the standard model gauge bosons.

hep-ph↗

arXiv2001

An effective lagrangian description of charged Higgs decays H^+ -> Wg, WZ and Wh

Charged Higgs decays are discussed within an effective lagrangian extension of the two-higgs doublet model, assuming new physics appearing in the Higgs sector of this model. Low energy constrains are used to imposse bounds on certain dimension -six operators that describe the modified charged Higgs interactions. These bounds are used then to study the decays H^+ -> Wg, WZ and Wh, which can have branching ratios of order 10^-5, 10^-1 and O(1), respectively; thse modes are thus sensitive probes of the symmetries of the Higgs sector that could be tested at future colliders.

hep-ph↗

arXiv2001

Photon photon scattering in a 3-3-1 model

We analyze the effects of a doubly charged vector bilepton as well as exotic quarks with charge 5/3 e and -4/3 e on light by light scattering. We consider mass values in the range 0.3--1 TeV, which would be reached at the planned future linear colliders. It is found that such exotic particles, especially the doubly charged vector bilepton, give raise to remarkable deviations from the standard model cross section. The virtual effects arising from these particles would provide an indirect test to a particular model which is based on the SU_c(3) X SU_L(3) X U_x(1) gauge symmetry, known as the 331 model, where such particles are a natural prediction.

hep-ph↗

arXiv2000

Trilinear Neutral Gauge Boson Couplings in Effective Theories

We list all the lowest dimension effective operators inducing off-shell trilinear neutral gauge boson couplings Z-Z-Photon, Z-Photon-Photon, and ZZZ within the effective Lagrangian approach, both in the linear and nonlinear realizations of the SU(2)_{L} X U(1)_Y gauge symmetry. In the linear scenario we find that these couplings can be generated only by dimension eight operators necessarily including the Higgs boson field, whereas in the nonlinear case they are induced by dimension six operators. We consider the impact of these couplings on some precision measurements such as the magnetic and electric dipole moments of fermions, as well as the Z boson rare decay Z -> neutrino+antineutrino+ photon. If the underlying new physics is of a decoupling nature, it is not expected that trilinear neutral gauge boson couplings may affect considerably any of these observables. On the contrary, it is just in the nonlinear scenario where these couplings have the more promising prospects of being perceptible through high precision experiments.

hep-ph↗

arXiv1999

Production of neutral and charged Higgs bosons of the MSSM at the future e-gamma colliders

A complete study for the production of neutral (h^0, H^0, A^0 (= ϕ^0_i)) and charged Higgs (H^\pm) bosons at electron-photon colliders is presented in the context of the minimal supersymmetric standard model. A particular choice of the non-linear R_ξgauge is used to evaluate the amplitudes of the reaction e-gamma --> e ϕ^0_i. The resulting cross section indicates that it will be possible to detect a signal from the neutral Higgs bosons for most regions of parameter space at the future linear colliders with \sqrt{s}=500 GeV through the reaction e gamma --> e ϕ^0_i. This reaction also offers the interesting possibility to measure the Higgs mass through the detection of the outgoing electron. The production of the charged Higgs boson through the reaction e gamma --> ν_e H^\pm$ has in general smaller values for the cross section, which seems more difficult to observe.

hep-ph↗

arXiv1999

Probing lepton flavour violation with Higgs boson decays H-> li+lj

We evaluate the lepton flavour violating (LFV) decays of HIggs bosons H->li+lj in several extensions of the SM, including both the effective lagrangian approach and several specific models. For the effective lagrangian case, we focus on dimension-six operators that induce LFV vertices for the Higgs and or Z bosons. For those operators whose coefficients can not be constrained by present data, LFV Higgs decays can have a B.R. of order 0.1-0.01. Those cases when current bounds apply, induce strong bounds for e-mu transitions, and the b.r. for H->e mu is of order 10^-9; however H->tau mu, tau e, can have B.R. of order 0.1. In the case of the two-higgs doublet model III, we obtain a similar B.R. for H-> tau mu, tau e, whereas in the SM with massive neutrinos and the minimal SUSY-SM the corresponding B.R. are very suppressed.

hep-ph↗

arXiv1999

Impacts of the bounds on the Higgs mass and m_W on effective theories

We study the inter-relations that exist between the present experimental bounds on the Higgs mass, as obtained from radiative corrections to $m_W$, and the effective parameters, $α_i$ and $Λ$. We find that the SM bounds on $m_H$, arising from a precise determination of the $m_W$ mass, can be substantially modified by the presence of dimension-6 operators which appear in the linear realization of the effective Lagrangian approach. A Higgs mass as heavy as 700 GeV can be allowed for scales of new physics of the order of 1 TeV.

hep-ph↗

arXiv1999

$γγ\to π^0 π^0$ as a test for the existence of a light $σ$ meson

We work out predictions of the Linear Sigma Model for the $γγ\toπ^0 π^0$ cross section. We consider the sigma width, which is introduced in a consistent way with chiral Ward identities. The results of Chiral Perturbation Theory are recovered in the $m_σ\to \infty$ limit. A fit to existing experimental results is consistent with a light and broad $σ$ meson.

hep-ph↗

arXiv1999

The decay Z -> neutrino antineutrino photon in the Standard Model

A complete study of the one-loop induced decay Z -> neutrino antineutrino photon is presented within the framework of the Standard Model. The advantages of using a nonlinear gauge are stressed. We have found that the main contributions come from the electric dipole and the magnetic dipole transitions of the Z gauge boson and the neutrino, respectively. We obtain a branching ratio B=7.16E-10, which is about four orders of magnitude smaller than the bound recentely obtained by the L3 collaboration and thus it leaves open a window to search for new physics effects in single-photon decays of the Z boson.

hep-ph↗

arXiv1997

Exact formulae for Higgs production through e gamma --> e H in the non-linear R_ξgauge

We study the production of the SM Higgs boson (H^0) at future e gamma colliders, through the reaction e gamma --> e H^0. The amplitude is evaluated using the non-linear R_ξgauge, which greatly simplifies the calculation. Complete analytical expressions for the amplitudes are presented, which include the contributions from 1-loop triangles "gamma gamma^* H^0" and "gamma Z^* H^0" as well as the W- and Z-boxes with their related $eeH^0$ triangle graphs. The resulting cross section for this mechanism indicates that it could be used to detect the Higgs signal and to test its properties.

hep-ph↗

arXiv1997

Tests of Higgs and Top Effective Interactions

We study the possibility to detect heavy physics effects in the interactions of Higgs bosons and the top quark at future colliders using the effective Lagrangian approach. The modification of the interactions may enhance the production of Higgs bosons at hadron colliders through the mechanisms of gluon fusion and associated production with a W boson or $t\bar{t}$ pairs. The most promising signature is through the decay of the Higgs boson into two photons, whose branching ratio is also enhanced in this approach. As a consequence of our analysis we get a bound on the chromomagnetic dipole moment of the top quark.

hep-ph↗

arXiv1996

New Physics Effects on Higgs Production at $γγ$ Colliders

We study heavy physics effects on the Higgs production in $γγ$ fusion using the effective Lagrangian approach. We find that the effects coming from new physics may enhance the standard model predictions for the number of events expected in the final states $\bar bb$, $WW$, and $ZZ$ up to one order of magnitude, whereas the corresponding number of events for the final state $\bar tt$ may be enhanced up to two orders of magnitude.

hep-ph↗

arXiv1995

Two Photon Processes and Effective Lagrangians with An Extended Scalar Sector

We consider the Standard Model with an extended scalar sector, and study the possible effects of the physics underlying such a model using an effective lagrangian parametrization. It is found that certain two photon processes offer windows where such heavy interactions might be glimpsed, but the realization of this expectation requires enormous experimental precision.

hep-ph↗