A custodial symmetry for Zbb

By K. Agashe, Roberto Contino, L. Rold, A. Pomarol. 2006

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We show that a subgroup of the custodial symmetry O(3) that protects �ρ from radiative corrections can also protect the Zbcoupling. This allows one to build models of electroweak symmetry breaking, such as Higgsless, Little Higgs or 5D composite Higgs models, that are safe from corrections to Z → bb. We show that when this symmetry protects Zbit cannot simultaneously protect Ztand W t ¯. Therefore one can expect to measure sizable deviations from the SM predictions of these couplings at future collider experiments. We also show under what circumstances ZbRR can receive corrections in the right direction to explain the anomaly in the LEP/SLD forward-backward asymmetry A b B.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/7c6e5c3eaf9a4184cb6a265a74d7261a7be2e11b

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Citations in the corpus

Fundamental composite dynamics: A review (2020, background): “We also notice that the component with the same quantum numbers of the quark doublet, present in both BA and BS, is always accompanied by a custodial doublet with which it forms a bi-doublet: this is one of the basic requirements to avoid large corrections to the Z couplings of the bottom quark [234”
Electroweak and Flavour Structure of a Warped Extra Dimension with Custodial Protection (2009, methodology): “In the EW sector, we consider the gauge symmetry [10, 11, 22]”
Composite scalar dark matter (2012, unknown): “In the case of the third family, the coupling λq′ L implies a correction to the SM value of the coupling ZbLbL, because it corresponds to T 3 R(bL) = 1/2 different from T 3 L(bL) = −1/2 [57]; we assume a small value λq′ L ∼ yb, to guarantee a small enough correction to ZbLbL.”
ΔF = 2 observables and fine-tuning in a warped extra dimension with custodial protection (2008, background): “15) allowing for consistency with EW precision data thanks to the protection of the ZbLb̄L coupling [15,16].”
Higgs boson from an extended symmetry (2007, background): “4) (11)Incidentally, for mQ = mX the BSM sector of the model has O(4) = SU(2)L×SU(2)R×PLR symmetry, which is known to protect the ZbLbL coupling [10].”