121 research outputs found
Testing models with non-minimal Higgs sector through the decay t->q+WZ
We study the contribution of charged Higgs boson to the rare decay of the top
quark t->q+WZ (q=d,s,b) in models with Higgs sector that includes doublets and
triplets. Higgs doublets are needed to couple charged Higgs with quarks,
whereas the Higgs triplets are required to generate the non-standard vertex HWZ
at tree-level. It is found that within a model that respect the custodial SU(2)
symmetry and avoids flavour changing neutral currents by imposing discrete
symmetries, the decay mode t->b+WZ, can reach a branching ratio of order
0.0178, whereas the decay modes t->(d,s)+WZ, can reach a similar branching
ratio in models where flavour changing neutral currents are suppressed by
flavour symmetries.Comment: Typeset using REVTEX and EPSF, 5 pag, 2 figure
Probing the mechanism of EWSB with a rho parameter defined in terms of Higgs couplings
A definition of the rho parameter based on the Higgs couplings with the gauge
bosons, rho_h= g_{hWW}}/c^2_W g_{hZZ}, is proposed as a new probe into the
origin of the mechanism of electroweak symmetry breaking. While
holds in the SM, deviations from one are predicted in models with extended
Higgs sector.
We derive a general expresion of rho_h for a model with arbitrary Higgs
multiplets, and discuss its size within the context of specific models with
Higgs triplets, including the ``Little Higgs'' models recently proposed. We
find the even for Higgs models that incorporate the custodial symmetry to make
rho=1, one could have rho_h\neq 1, which could be tested at the level of a few
percent, with the precision Higgs meassurements expected at the NLC.Comment: 12 pages, 2 figure
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.Comment: 15 pages, 3 figure
New Higgs signals induced by mirror fermion mixing effects
We study the conditions under which flavor violation arises in scalar-fermion
interactions, as a result of the mixing phenomena between the standard model
and exotic fermions. Phenomenological consequences are discussed within the
specific context of a left-right model where these additional fermions have
mirror properties under the new SU(2)_R gauge group.
Bounds on the parameters of the model are obtained from LFV processes; these
results are then used to study the LFV Higgs decays (H --> tau l_j, l_j = e,
mu), which reach branching ratios that could be detected at future colliders.Comment: 12 pages, 2 figures, ReVTex4, graphicx, to be published in Phys. Rev.
Mass matrix Ansatz and lepton flavor violation in the THDM-III
Predictive Higgs-fermion couplings can be obtained when a specific texture
for the fermion mass matrices is included in the general two-Higgs doublet
model. We derive the form of these couplings in the charged lepton sector using
a Hermitian mass matrix Ansatz with four-texture zeros. The presence of
unconstrained phases in the vertices phi-li-lj modifies the pattern of
flavor-violating Higgs interactions. Bounds on the model parameters are
obtained from present limits on rare lepton flavor violating processes, which
could be extended further by the search for the decay tau -> mu mu mu and mu-e
conversion at future experiments. The signal from Higgs boson decays phi -> tau
mu could be searched at the large hadron collider (LHC), while e-mu transitions
could produce a detectable signal at a future e mu-collider, through the
reaction e mu -> h0 -> tau tau.Comment: 17 pages, 9 figure
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 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.Comment: 14 pages, Latex, two figures available by fax under request. To be
published in Phys. Lett
Chromomagnetic Dipole Moment of the Top Quark Revisited
We study the complete one-loop contributions to the chromagnetic dipole
moment of the top quark in the Standard Model, two Higgs doublet
models, topcolor assited technicolor models (TC2), 331 models and extended
models with a single extra dimension. We find that the SM predicts
and that the predictions of the other models are also
consitent with the constraints imposed on by low-energy
precision measurements.Comment: 20 pages, 5 figures, Updat
FCNC Top Quark Decays in Extra Dimensions
The flavor changing neutral top quark decay t -> c X is computed, where X is
a neutral standard model particle, in a extended model with a single extra
dimension. The cases for the photon, X= \gammaR_\xi gauge. We find that
the branching ratios can be enhanced by the dynamics originated in the extra
dimension. In the limit where 1/R >> ->, we have found Br(t -> c \gamma) \simeq
10^{-10} for 1/R = 0.5 TeV. For the decay t -> c H, we have found Br(t -> cH)
\simeq 10^{-10} for a low Higgs mass value. The branching ratios go to zero
when 1/R -> \infty.Comment: Accepted to be published in the Europ. Phys. Jour. C; 16 pages, 2
figure
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.Comment: References added, final version to appear in Physical Review
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