Top-antitop production from W_(L)^(+)W_(L)^(-) and Z_(L)_Z(L) scattering under a strongly interacting symmetry-breaking sector

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Castillo, Andrés
Delgado López, Rafael
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By considering a non-linear electroweak chiral Lagrangian, including the Higgs, coupled to heavy quarks, and the equivalence theorem, we compute the one-loop scattering amplitudes W^(+)W^(−) → tṫ, Z Z → tṫ and hh → tṫ (in the regime M^(2)_(t)/v^(2) « √sM_(t)/v^(2) « s/v^(2) and to NLO in the effective theory). We calculate the scalar partial-wave helicity amplitudes which allow us to check unitarity at the perturbative level in both M_(t) /v and s/v. As with growing energy perturbative unitarity deteriorates, we also introduce a new unitarization method with the right analytical behavior on the complex s-plane and that can support poles on the second Riemann sheet to describe resonances in terms of the Lagrangian couplings. Thus we have achieved a consistent phenomenological description of any resonant tṫ production that may be enhanced by a possible strongly interacting electroweak symmetry breaking sector.
© The Author(s) 2017. The authors thank useful conversations with D. Espriu, M.J. Herrero and J.J. Sanz-Cillero, and the very constructive and useful comments of an anonymous referee. A. Dobado thanks the CERN TH-Unit for its hospitality during the time some important parts of this work were done. R.L. Delgado thanks the SLAC Theory Group for its hospitality and encouragement. The work has been supported by the Spanish Grants No. UCM: 910309, MINECO: FPA2014-53375- C2-1-P and FPA2016-75654-C2-1-P, and by the grant MINECO: BES- 2012- 056054 (R.L. Delgado). A. Castillo is indebted to the Programa Nacional Doctoral of Colciencias-567 for its academic and financial support and also thanks kind hospitality and encouragement of the Group of Effective Theories in Modern Physics at the Universidad Complutense de Madrid.
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