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  • Letter
  • Open Access

Large t→cZ as a sign of vectorlike quarks in light of the W mass

Andreas Crivellin1,2,*, Matthew Kirk3,†, Teppei Kitahara4,5,6,‡, and Federico Mescia3,§

  • 1Physik-Institut, Universität Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland
  • 2Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
  • 3Departament de Física Quàntica i Astrofísica (FQA), Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (UB), 08028 Barcelona, Spain
  • 4Institute for Advanced Research, Nagoya University, Nagoya 464-8601, Japan
  • 5Kobayashi-Maskawa Institute for the Origin of Particles and the Universe, Nagoya University, Nagoya 464-8602, Japan
  • 6Theory Center, IPNS, High Energy Accelerator Research Organization (KEK), Tsukuba 305-0801, Japan

  • *andreas.crivellin@cern.ch
  • †mjkirk@icc.ub.edu
  • ‡teppeik@kmi.nagoya-u.ac.jp
  • §mescia@ub.edu
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Phys. Rev. D 106, L031704 – Published 17 August, 2022

DOI: https://doi.org/10.1103/PhysRevD.106.L031704

Abstract

The rare flavor-changing top quark decay t→cZ is a clear sign of new physics and experimentally very interesting due to the huge number of top quarks produced at the LHC. However, there are few (viable) models which can generate a sizable branching ratio for t→cZ—in fact vectorlike quarks seem to be the only realistic option. In this paper, we investigate all three representations (under the Standard Model gauge group) of vectorlike quarks (U, Q1 and Q7) that can generate a sizable branching ratio for t→cZ without violating bounds from B physics. Importantly, these are exactly the three vectorlike quarks which can lead to a sizable positive shift in the prediction for W mass, via the couplings to the top quark also needed for a sizable Br(t→cZ). Calculating and using the one-loop matching of vectorlike quarks on the Standard Model effective field theory, we find that Br(t→cZ) can be of the order of 10−6, 10−5 and 10−4 for U, Q1 and Q7, respectively, and that in all three cases the large W mass measurement can be accommodated.

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Phys. Rev. D 106, L031704– Published 17 August, 2022
  • Received 14 April 2022
  • Accepted 4 August 2022
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