Addressing the CKM unitarity problem with a vector-like up quark

Branco, G.C.; Penedo, J. T.; Pereira, Pedro M. F.; Rebelo, M. N.; Silva-Marcos, J. I.

doi:10.1007/jhep07(2021)099

Cited by 47 publications

(37 citation statements)

References 73 publications

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“…We first note that only the three representations U , D, or Q 1 (with couplings to both up and down quarks) can explain the CAA [1,[63][64][65] due to their mixing with the SM quarks, while, on the other hand, T 1 or T 2 worsen the CAA. EWPO places multi-TeV mass limits on the VLQs U , D, and Q 1 (for couplings fixed to unity), which come close to ruling out the best-fit regions from the CAA for U and D, while there is actually a small (1σ) preference for the other representations (Q 5,7 and T 1,2 ) driven by R 0 e and R 0 µ .…”

Section: Vector-like Quarksmentioning

confidence: 96%

“…While the anomalies in semi-leptonic B decays and the anomalous magnetic moment of the muon point towards NP related to second-and third-generation fermions, the CAA and the CMS di-lepton excess can be related to first-generation quarks and leptons, with simultaneous explanations possible in terms of the effective dimension-6 operator Q (3) q [62]. Similarly, explanations of the CAA via modified W -u-d couplings also require NP related to first generation-quarks [1,[63][64][65]. In this paper, we take the large array of complementary measurements sensitive to first-generation NP, together with hints for potential NP effects, as motivation to perform a combined analysis, concentrating on possible correlations among the processes listed above.…”

Section: Introductionmentioning

confidence: 99%

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First-generation new physics in simplified models: from low-energy parity violation to the LHC

Crivellin

Hoferichter

Kirk

et al. 2021

J. High Energ. Phys.

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New-physics (NP) constraints on first-generation quark-lepton interactions are particularly interesting given the large number of complementary processes and observables that have been measured. Recently, first hints for such NP effects have been observed as an apparent deficit in first-row CKM unitarity, known as the Cabibbo angle anomaly, and the CMS excess in $$ q\overline{q} $$ q q ¯ → e+e−. Since the same NP would inevitably enter in searches for low-energy parity violation, such as atomic parity violation, parity-violating electron scattering, and coherent neutrino-nucleus scattering, as well as electroweak precision observables, a combined analysis is required to assess the viability of potential NP interpretations. In this article we investigate the interplay between LHC searches, the Cabibbo angle anomaly, electroweak precision observables, and low-energy parity violation by studying all simplified models that give rise to tree-level effects related to interactions between first-generation quarks and leptons. Matching these models onto Standard Model effective field theory, we derive master formulae in terms of the respective Wilson coefficients, perform a complete phenomenological analysis of all available constraints, point out how parity violation can in the future be used to disentangle different NP scenarios, and project the constraints achievable with forthcoming experiments.

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Section: Vector-like Quarksmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

First-generation new physics in simplified models: from low-energy parity violation to the LHC

Crivellin

Hoferichter

Kirk

et al. 2021

J. High Energ. Phys.

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show abstract

“…Following [9], we propose here a solution for CKM unitary problem where it is assumed that s 14 = O(λ 2 ), with λ = |V us |.…”

Section: Salient Features Of S 14 − Dominancementioning

confidence: 99%

“…It has been pointed out that one of the simplest extensions of the SM which can account for this NP, consists of the addition of either one down-type [8] or one up-type [9] vector-like quark (VLQ). In the case of a down-type VLQ the CKM matrix consists of the first 3 rows of a unitary 4 × 4 matrix, while in the case of an up-type VLQ, it consists of the first 3 columns of a 4 × 4 unitary matrix.…”

Section: Introductionmentioning

confidence: 99%

Decays of the Heavy Top and New Insights on $ε_K$ in a one-VLQ Minimal Solution to the CKM Unitarity Problem

Botella,

Branco,

Rebelo

et al. 2021

Preprint

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We propose a minimal extension of the Standard Model where an up-type vector-like quark, denoted T , is introduced and provides a simple solution to the CKM unitarity problem. We adopt the Botella-Chau parametrization in order to extract the 4 × 3 quark mixing matrix which contains the three angles of the 3 × 3 CKM matrix plus three new angles denoted θ 14 , θ 24 , θ 34 . It is assumed that the mixing of T with standard quarks is dominated by θ 14 .Imposing a recently derived, and much more restrictive, upper-bound on the New Physics contributions to ε K , we find, in the limit of exact θ 14 dominance where the other extra angles vanish, that ε NP K is too large. However, if one relaxes the exact θ 14 dominance limit, there exists a parameter region, where one may obtain ε NP K in agreement with experiment while maintaining the novel pattern of T decays with the heavy quark decaying predominantly to the light quarks d and u. We also find a reduction in the decay rate of K L → π o νν.

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“…The hypothetical VLQs could explain this misalignment between the SM predictions and observed data; this note will address this Beyond Standard Model (BSM) scenario. This class of models can indeed naturally lead to deviations from the CKM unitarity capable of accommodating the recent measurements of |V us | and |V ud | [1,3]. Vector-like quarks (VLQs) are spin 1/2 particles characterised by having the left-and right-handed components defined by the same colour and electroweak quantum numbers.…”

Section: Introductionmentioning

confidence: 96%