Unitarity Constraints on Anomalous Top Quark Couplings to Weak Gauge Bosons

Abstract

If there is new physics associated with the top quark, it could show up as anomalous couplings of the top quark to weak gauge bosons, such as $Z\ttbar$ and $W\tbbar$ vector and axial-vector couplings. We use the processes $\ttbar\to Z^0Z^0$, $\ttbar\to W^+W^-$, and $\ttbar\to Z^0H$ to obtain the unitarity constraints on these anomalous couplings, and combine these constraints with those from precision electroweak data. The unitarity constraints can impose additional limits on the anomalous couplings when the scale of new physics is as low as 2 TeV. A nonzero measurement of such an anomalous coupling leads to an upper limit on the new physics scale from the unitarity condition.

12 pages, Latex, 4 postscipt figures included. Resubmitted with major revisions, including the newest data on $R_b$

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• The Waning of the WIMP: Endgame?
• Measurement of the Helicity of W Bosons in Top Quark Decays
• Improved Measurement of ttZ Couplings at the LHC
• CP Violation in B Decays from Anomalous tbW Interactions
• Review of Properties of the Top Quark from Measurements at the Tevatron
• Probing anomalous top quark couplings at eγcolliders
• Semileptonic decays of polarised top quarks: V + A admixture and QCD corrections
• Search for Anomalous Couplings in Top Decay at Hadron Colliders
• How heavy can dark matter be? Constraining colourful unitarity with SARAH
• CP-odd static electromagnetic properties of the W gauge boson and the t quark via the anomalous tbW coupling
• A Model-independent Description of New Physics effects in e+e- to t tbar
• Using e-e+ to b b(bar) to test properties of new interactions at LEP2 and higher energies