The rare flavor-changing top quark decay t →c Z 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 →c Z —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 →c Z 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 →c Z ) . Calculating and using the one-loop matching of vectorlike quarks on the Standard Model effective field theory, we find that Br (t →c Z ) 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.
Physical Review D
- Pub Date:
- August 2022
- High Energy Physics - Phenomenology;
- High Energy Physics - Experiment;
- High Energy Physics - Theory
- 8 pages, 2 figures + supplemental material. v2: Accepted to PRD, discussion of future lepton colliders added, units corrected in eq II.9, further references added