Determining the space-time structure of bottom-quark couplings to spin-zero particles release_c3e3rsdh5nennp7sn2dodo2qma

by Tathagata Ghosh, Rohini Godbole, Xerxes Tata

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We present a general argument that highlights the difficulty of determining the space-time structure of the renormalizable bottom quark Yukawa interactions of the Standard Model Higgs boson, or for that matter of any hypothetical spin-zero particle, at high energy colliders. The essence of the argument is that, it is always possible, by chiral rotations, to transform between scalar and pseudoscalar Yukawa interactions without affecting the interactions of bottom quarks with SM gauge bosons. Since these rotations affect only the b-quark mass terms in the Standard Model Lagrangian, any differences in observables for scalar versus pseudoscalar couplings vanish when m_b → 0, and are strongly suppressed in high energy processes involving the heavy spin-zero particle where the b-quarks are typically relativistic. We show, however, that the energy dependence of, for instance, e^+e^- → bb̅ X (here X denotes the spin-zero particle) close to the reaction threshold may serve to provide a distinction between the scalar versus pseudoscalar coupling at electron-positron colliders that are being proposed, provided that the Xbb̅ coupling is sizeable. We also note that while various kinematic distributions for t t̅ h are indeed sensitive to the space-time structure of the top Yukawa coupling, for a spin-0 particle X of an arbitrary mass, the said sensitivity is lost if m_X >> m_t.
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Type  report
Stage   submitted
Date   2019-04-22
Version   v1
Language   en ?
Number  UH-511-1304-19
arXiv  1904.09895v1
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