We show that the precise determination of the Tau magnetic properties is possible in the next generation accelerators, specially at B/Flavour factories. We define spin correlation observables ...suitable to extract the real part of the magnetic form factor that, for the first time, will allow to test the standard model-QED predictions. In particular, the predicted QED-dependence with both the momentum transfer and the lepton mass can be precisely measured. Until now, the most stringent bounds on the \(\tau\) magnetic moment \(a_\tau\) come from LEP data with strong assumptions on the physics involved on the observed process. In this paper, we find three different combinations of spin correlations of the outgoing Taus that disentangle the magnetic moment form factor of the Tau lepton in the electromagnetic vertex. These combinations of asymmetries also get rid off the contributions coming from Z-mediating amplitudes to the defined correlations. Using unpolarized electron beams and an integrated luminosity of \(15 \times 10^{18} b^{-1}\), the sensitivity to the \(\tau\) magnetic moment form factor is of the order \(10^{-6}\). This sensitivity is two orders of magnitude better than the present existing high- or low-energy bounds on the magnetic moment and would allow its actual measurement with the precision of a few per cent.
The proposed high-luminosity B/Flavor factories offer new opportunities for the improved determination of the fundamental physical parameters of standard heavy leptons. Compared to the electron or ...the muon case, the magnetic properties of the \(\tau\) lepton are largely unexplored. We show that the electromagnetic properties of the \(\tau\), and in particular its magnetic form factor, may be measured competitively in these facilities, using unpolarized or polarized electron beams. Various observables of the \(\tau\)'s produced on top of the \(\Upsilon\) resonances, such as cross-section and normal polarization for unpolarized electrons or longitudinal and transverse asymmetries for polarized beams, can be combined in order to increase the sensitivity on the magnetic moment form factor. In the case of polarized electrons, we identify a special combination of transverse and longitudinal \(\tau\) polarizations able to disentangle this anomalous magnetic form factor from both the charge form factor and the interference with the Z-mediating amplitude. For an integrated luminosity of \(15 \times 10^{18} b^{-1}\) one could achieve a sensitivity of about \(10^{-6}\), which is several orders of magnitude below any other existing high- or low-energy bound on the magnetic moment. Thus one may obtain a QED test of this fundamental quantity to a few % precision.
Nucl.Phys.B763:283-292,2007 The new proposals for high luminosity B/Flavor factories, near and on top of
the $\Upsilon$ resonances, allow for a detailed investigation of CP-violation
in the ...$\tau$-pair production. In particular, bounds on the tau electric dipole
moment can be obtained from genuine CP-odd observables related to the
$\tau$-pair production. We perform an independent analysis from low energy (10
GeV) data by means of linear spin observables. We show that, for a
longitudinally polarized electron beam, a CP-odd asymmetry, associated to the
normal polarization term, can be measured at these low energy facilities both
at resonant and non resonant energies. In this way, stringent and independent
bounds to the tau electric dipole moment, which are orders of magnitude below
other high or low energy bounds, can be obtained.
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= ...\gamma$, and a Standard Model Higgs
boson, X = H, are analyzed in detail in a non-linear$R_\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.
High luminosity Super B/Flavor factories, near and on top of the $\Upsilon$
resonances, allow for a detailed investigation of CP-violation in $\tau$
physics. In particular, bounds on the $\tau$ ...electric dipole moment can be
obtained from CP-odd observables. We perform an independent analysis from other
low and high energy data. For polarized electron beam a CP-odd asymmetry,
associated to the normal polarization term, can be used to set stringent bounds
on the $\tau$ electric dipole moment.
Phys.Rev. D71 (2005) 115003 We study the effect of new physics on the Z-decay into b anti-b pairs in the
framework of 331 models. The decay Z -> b anti-b is computed at one loop level
and, using ...previous results, we evaluate this branching fraction in the
framework of 331 models. A wide range of the space parameter of the model is
considered and possible deviations from the standard model predictions are
explored. From precision measurements at the Z-pole we find the allowed region
for MJ3, MX at 95 % CL.
Phys.Rev.D71:035003,2005 We calculate the two body Higgs boson decays in the framework of the littlest
Higgs model. The decay $H \to \gamma Z$ is computed at one loop level and,
using previous ...results, we evaluate the branching fractions in the framework of
the littlest Higgs model. A wide range of the space parameter of the model is
considered and possible deviations from the standard model are explored.
Nucl.Phys. B701 (2004) 87-102 CP violation at low energy is investigated at the tau electromagnetic vertex.
High statistics at B factories, and on top of the Upsilon resonances, allows a
detailed ...investigation of CP-odd observables related to the tau-pair
production. The contribution of the tau electric dipole moment is considered in
detail. We perform an analysis independent from the high energy data by means
of correlation and linear spin observables at low energy. We show that
different CP-odd asymmetries, associated to the normal-transverse and
normal-longitudinal correlation terms can be measured at low energy
accelerators, both at resonant and non resonant energies. These observables
allow to put stringent and independent bounds to the tau electric dipole moment
that are competitive with other high or low energy results.
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= ...\gamma\(, and a Standard Model Higgs boson, X = H, are analyzed in detail in a non-linear\)R_\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.
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