Vector-like quark interpretation for the CKM unitarity violation, excess in Higgs signal strength, and bottom quark forward-backward asymmetry

A bstract Due to a recent more precise evaluation of V ud and V us , the unitarity condition of the first row in the Cabibbo-Kobayashi-Maskawa (CKM) matrix: |V ud | 2 + |Vus| 2 + |V ub | 2 = 0 . 99798 ± 0 . 00038 now stands at a deviation more than 4 σ from unity. Furthermore, a mild excess in the o...

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Bibliographic Details
Published in:The journal of high energy physics 2020-05, Vol.2020 (5), p.1-28, Article 117
Main Authors: Cheung, Kingman, Keung, Wai-Yee, Lu, Chih-Ting, Tseng, Po-Yan
Format: Article
Language:English
Subjects:
Anomalies
Asymmetry
Beyond Standard Model
Classical and Quantum Gravitation
Constraint modelling
Elementary Particles
Heavy Quark Physics
Higgs Physics
High energy physics
Large Hadron Collider
Physics
Physics and Astronomy
Quantum Field Theories
Quantum Field Theory
Quantum Physics
Quark Masses and SM Parameters
Quarks
Regular Article - Theoretical Physics
Relativity Theory
Signal strength
Standard model (particle physics)
String Theory
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Summary:A bstract Due to a recent more precise evaluation of V ud and V us , the unitarity condition of the first row in the Cabibbo-Kobayashi-Maskawa (CKM) matrix: |V ud | 2 + |Vus| 2 + |V ub | 2 = 0 . 99798 ± 0 . 00038 now stands at a deviation more than 4 σ from unity. Furthermore, a mild excess in the overall Higgs signal strength appears at about 2 σ above the standard model (SM) prediction, as well as the long-lasting discrepancy in the forward-backward asymmetry A FB b in Z → b b ¯ at LEP. Motivated from the above three anomalies we investigate an extension of the SM with vector-like quarks (VLQs) associated with the down-quark sector, with the goal of alleviating the tension among these datasets. We perform global fits of the model under the constraints coming from the unitarity condition of the first row of the CKM matrix, the Z -pole observables A FB b , R b and Γ had , Electro-Weak precision observables ∆ S and ∆ T , B -meson observables B d 0 − B ¯ d 0 mixing, B + → π + ℓ + ℓ − and B 0 → μ + μ − and direct searches for VLQs at the Large Hadron Collider (LHC). Our results suggest that adding VLQs to the SM provides better agreement than the SM.
ISSN:1029-8479
1029-8479
DOI:10.1007/JHEP05(2020)117