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Eligibility of EFT Approach to Search for tqg FCNC Phenomenon

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Abstract

The Effective Field Theory (EFT) approach is widely used in the search for possible deviations from the predictions of the Standard Model. Such an approximation of possible BSM physics is valid up to a certain levels of energy scale and accuracy. In this article, we investigate potential limitation of the EFT approach related to unitarity to describe possible contributions of flavor-changing neutral currents (FCNC) involving the top quark. The numerical and analytical calculations of the FCNC processes used in the EFT approach demonstrate the constant asymptotic behavior of the total cross section with increasing energy. It is shown that the EFT approach for studying the possible contribution of FCNC does not violate the restrictions following from perturbative unitarity, the asymptotic behavior of the cross section does not exceed the Froissart bound, and the approach itself can be used to set the corresponding experimental limits for FCNC couplings or Wilson coefficients at present and future colliders.

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Notes

  1. The Lagrangian describing the tree–point (tqg) and the four-point (tqgg) interaction vertices (tqg) as well as corresponding Feynman rules were presented in [4]. The Lagrangian describing not only the tree point vertex (tqg), but also the interaction vertex with the Higgs boson (tqgh) as follows from the dimension 6 operators was worked out in [5].

  2. Note that the four-point vertex of the gluon–gluon–top quark–\(u\) quark interaction from (3) was implemented in CompHEP using an auxiliary color octet field with spin two \(t_{\mu\nu}^{a}\), denoted as \(G.t\) in CompHEP, with the propagator defined by the Lagrangian \(-\frac{1}{2}t_{\mu\nu}^{a}t^{\mu\nu}_{a}\). It should be noted that the four-point vertex is necessary for gauge invariance in calculating the contributions with the initial states \(gg\) and \(gu\).

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ACKNOWLEDGMENTS

The work was supported by grant no. 16-12-10280 of the Russian Science Foundation.

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  1. Skobeltsyn Institute of Nuclear Physics, Moscow State University, Moscow, Russia

    E. E. Boos, V. E. Bunichev, L. V. Dudko, M. A. Perfilov & G. A. Vorotnikov

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  1. E. E. Boos
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  2. V. E. Bunichev
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  3. L. V. Dudko
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  4. M. A. Perfilov
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  5. G. A. Vorotnikov
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Correspondence to E. E. Boos, V. E. Bunichev, L. V. Dudko, M. A. Perfilov or G. A. Vorotnikov.

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Boos, E.E., Bunichev, V.E., Dudko, L.V. et al. Eligibility of EFT Approach to Search for tqg FCNC Phenomenon. Phys. Atom. Nuclei 83, 984–988 (2020). https://doi.org/10.1134/S1063778820060083

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