Datta, A. ; Drees, M. ; Godbole, R. M. ; Tata, X. R.
(1988)
*Do data on W and Z decays already constrain nonstandard physics?*
Physical Review D, 37
(7).
pp. 1876-1891.
ISSN 0556-2821

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Official URL: http://prd.aps.org/abstract/PRD/v37/i7/p1876_1

Related URL: http://dx.doi.org/10.1103/PhysRevD.37.1876

## Abstract

We study the predictions of several extensions of the standard model (SM) for the ratio R=N(pp^{-}→W→eν)/N(pp^{-}→Z→e^{+}e^{-}). The starting point of our investigation is the observation that the SM prediction for R seems to be somewhat above the data, especially if the top quark is heavy. We first show that this situation is not changed qualitatively by the incorporation of full quark-mass-dependent QCD corrections for Γ_{W} and Γ_{Z}. However, if either gauginos or exotic E(6) leptons with suitably chosen masses and mixings are present, the prediction for R can be reduced by 0.5-0.7 units. A similar reduction is possible if the Z boson mixes with the Z'boson present in certain SO(10) and E(6) models. For large top masses the reduction of R can be even larger if the b quark has a sizable SU(2)-singlet component, which is possible in superstring-inspired E(6) models. However, sleptons or squarks cannot reduce the prediction for R, and in models with two Higgs doublets R is expected to be close to its SM value. We then show that existing data strongly disfavor a sequential down-type quark below 26 GeV, and derive limits on the V_{tb} element of the extended Kobayashi-Maskawa mixing matrix of four-generation models. We also show that the data on R together with existing bounds on the ρ parameter severely constrain models of four-generation quark mass matrices. Furthermore, we find that the simultaneous existence of a light photino and a chargino with mass below M_{Z}/2 is strongly disfavored. We finally discuss the possible effects of new physics on the bounds on the top-quark mass and the number of light neutrino species that can be derived from the experimental upper bound on R.

Item Type: | Article |
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Source: | Copyright of this article belongs to American Physical Society. |

ID Code: | 14329 |

Deposited On: | 12 Nov 2010 08:23 |

Last Modified: | 02 Jun 2011 07:27 |

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