We present new, model-independent analyses of the observables in low-energy neutral-current experiments in the neutrino-hadron, neutrino-electron, electron/muon-hadron and electron- muon/tau sectors. We combine them with the latest experimental measurements of the W and Z masses to make global fits in the context of the standard model and of superstring-inspired models. We find in the standard model that sin2θw = 0.004 if ρ{variant} is fixed to be 1, whilst a two parameter fit yields sin2θw = 0.229 ± 0. 006 and ρ{variant} = 1.001 ± 0.007. This new value of sin2θw for ρ{variant} = 1 lies uncomfortably outside the predicted region of the minimal SU(5) model, but is consistent with supersymmetric SU(5) models. In the minimal standard model with ρ{variant} = 1 and equal Higgs and Z masses we find that mt<168 GeV at the 90% confidence level. We establish lower bounds on the masses of additional neutral gauge bosons Z' in three superstring-inspired models and upper limits on their mixing with the standard model Z0. In particular, we find that mZ'>129 GeV at the 90% confidence level in a minimal rank-5 superstring-inspired model with canonical Higgs structure. © 1988.
Neutral currents within and beyond the standard model
ZWIRNER, FABIO
1988
Abstract
We present new, model-independent analyses of the observables in low-energy neutral-current experiments in the neutrino-hadron, neutrino-electron, electron/muon-hadron and electron- muon/tau sectors. We combine them with the latest experimental measurements of the W and Z masses to make global fits in the context of the standard model and of superstring-inspired models. We find in the standard model that sin2θw = 0.004 if ρ{variant} is fixed to be 1, whilst a two parameter fit yields sin2θw = 0.229 ± 0. 006 and ρ{variant} = 1.001 ± 0.007. This new value of sin2θw for ρ{variant} = 1 lies uncomfortably outside the predicted region of the minimal SU(5) model, but is consistent with supersymmetric SU(5) models. In the minimal standard model with ρ{variant} = 1 and equal Higgs and Z masses we find that mt<168 GeV at the 90% confidence level. We establish lower bounds on the masses of additional neutral gauge bosons Z' in three superstring-inspired models and upper limits on their mixing with the standard model Z0. In particular, we find that mZ'>129 GeV at the 90% confidence level in a minimal rank-5 superstring-inspired model with canonical Higgs structure. © 1988.Pubblicazioni consigliate
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