Global Fit of Modified Quark Couplings to EW Gauge Bosons and Vector-Like Quarks in Light of the Cabibbo Angle Anomaly

Abstract

There are two tensions related to the Cabibbo angle of the CKM matrix. First, the determinations of $V_{us}$ from $K_{\mu 2}$, $K_{\ell 3}$, and $\tau$ decays disagree at the $3\sigma$ level. Second, using the average of these results in combination with $\beta$ decays (including super-allowed $\beta$ decays and neutron decay), a deficit in first-row CKM unitarity with a significance of again about $3\sigma$ is found. These discrepancies, known as the Cabibbo Angle anomaly, can in principle be solved by modifications of $W$ boson couplings to quarks. However, due to $SU(2{)}_L$ invariance, $Z$ couplings to quarks are also modified and flavour changing neutral currents can occur. In order to consistently assess the agreement of a new physics hypothesis with data, we perform a combined analysis for all dimension-six Standard Model Effective Field Theory operators that generate modified $W$ couplings to first and second generation quarks. We then study models with vector-like quarks, which are prime candidates for a corresponding UV completion as they can affect $W$-quark couplings at tree level, and we perform a global fit including flavour observables (in particular loop effects in $\Delta F=2$ processes). We find that the best fit can be obtained for the $SU(2{)}_L$ doublet vector-like quark $Q$ as it can generate right-handed $W$-$u$-$d$ and $W$-$u$-$s$ couplings as preferred by data.

46 pages, 16 figures. v2: Added references, minor numerical changes due to bug in code, conclusions unchanged. v3: journal version, minor clarifications added

References in corpus (44)

• FLAG Review 2021
• Two-Loop Electroweak Corrections for the K -> pi nu anti-nu Decays
• Measurement of the Weak Axial-Vector Coupling Constant in the Decay of Free Neutrons Using a Pulsed Cold Neutron Beam
• Precision Measurement of the Weak Charge of the Proton
• Improved estimates of rare K decay matrix-elements from Kl3 decays
• Epsilon_K at Next-to-Next-to-Leading Order: The Charm-Top-Quark Contribution
• A Guaranteed Discovery at Future Muon Colliders
• Standard Model $\mathcal{O}(\alpha )$ renormalization of $g_A$ and its impact on new physics searches
• Global Electroweak Fit and Vector-Like Leptons in Light of the Cabibbo Angle Anomaly
• Improved Bhabha cross section at LEP and the number of light neutrino species
• Consequences of chirally enhanced explanations of $(g-2{)}_{\mu }$ for $h\to \mu \mu$ and $Z\to \mu \mu$
• Expectations for the muon g-2 in simplified models with dark matter
• Electroweak axial structure functions and improved extraction of the $V_{ud}$ CKM matrix element
• Dispersive representation and shape of the Kl3 form factors: robustness
• Scrutinizing CKM unitarity with a new measurement of the $K_{\mu 3}/K_{\mu 2}$ branching fraction
• First-principles calculation of electroweak box diagrams from lattice QCD
• The Fermi constant from muon decay versus electroweak fits and CKM unitarity
• Cabibbo anomaly versus electroweak precision tests: An exploration of extensions of the Standard Model
• Explaining $b\to s{\ell }^{+}{\ell }^{-}$ and the Cabibbo Angle Anomaly with a Vector Triplet
• A No-Lose Theorem for Discovering the New Physics of $(g-2{)}_{\mu }$ at Muon Colliders
• Are the CKM anomalies induced by vector-like quarks? Limits from flavor changing and Standard Model precision tests
• Addressing the CKM Unitarity Problem with a Vector-like Up Quark
• First-Generation New Physics in Simplified Models: From Low-Energy Parity Violation to the LHC
• Unveiling Hidden Physics at the LHC
• |V_us| and m_s from hadronic tau decays
• Muon and electron g-2 and proton and cesium weak charges implications on dark ${\mathbf{Z}}_{\mathbf{d}}$ models
• Large $t\to cZ$ as a Sign of Vector-Like Quarks in Light of the $W$ Mass
• Tests of non-standard electroweak couplings of right-handed quarks
• Mounting Evidence for the Violation of Lepton Flavor Universality
• SU(3)-breaking corrections to the hyperon vector coupling $f_1(0)$ in covariant baryon chiral perturbation theory
• Testing Lepton Flavor Universality with Pion, Kaon, Tau, and Beta Decays
• Complete theory of radiative corrections to $K_{\ell 3}$ decays and the $V_{us}$ update
• Status of the fourth fermion generation before ICHEP2012: Higgs data and electroweak precision observables
• High-precision determination of the $K_{e3}$ radiative corrections
• Radiative corrections to $\tau \to \pi (K){\nu }_{\tau }[\gamma ]$: a reliable new physics test
• Leptoquark-vectorlike quark model for the CDF $m_W$, $(g-2{)}_{\mu }$, $R_{K^{(\ast )}}$ anomalies and neutrino mass
• Leptonic $g-2$ moments, CP phases and the Higgs boson mass constraint
• What is the scale of new physics behind the muon $g-2$?
• Asymmetry in flavour changing electromagnetic transitions of vector-like quarks
• Systematic approach to $B$-physics anomalies and $t$-channel dark matter
• Electroweak Corrections to the Charm-Top-Quark Contribution to ${\epsilon }_K$
• One-loop determination of $\tau \to \pi (K){\nu }_{\tau }[\gamma ]$ branching ratios and new physics tests
• Search for pair production of the heavy vectorlike top partner in same-sign dilepton signature at the HL-LHC
• High-energy frontier of the muon g-2 at a muon collider

Cited by in corpus (22)

• FLAG Review 2024
• Vector-like Singlet Quarks: a Roadmap
• Anomalies in Particle Physics
• The Importance of Flavor in SMEFT Electroweak Precision Fits
• An $\text{ab initio}$ strategy for taming nuclear-structure dependence of $V_{ud}$ extractions: the ${}^{10}\mathrm{C}\to {}^{10}\mathrm{B}$ superallowed transition
• Minimal model for the $W$-boson mass, $(g-2{)}_{\mu }$, $h\to {\mu }^{+}{\mu }^{-}$ and quark-mixing-matrix unitarity
• Correlating New Physics Effects in Semileptonic $\Delta C=1$ and $\Delta S=1$ Processes
• Global analysis and LHC study of a vector-like extension of the Standard Model with extra scalars
• Constraining $|V_{cs}|$ and physics beyond the Standard Model from exclusive (semi)leptonic charm decays
• Search for single vector-like $B$ quark production in hadronic final states at the LHC
• From the EFT to the UV: the complete SMEFT one-loop dictionary
• Theoretical point of view on Cabibbo angle anomaly
• MeV Sterile Neutrino in light of the Cabibbo-Angle Anomaly
• Vector-like quark doublets, weak-basis invariants and CP violation
• Cabibbo angle anomalies and a global fit to vector-like quarks
• Exploring vector-like $B$-quark pair production at CLIC in fully hadronic final states
• Testing the CKM unitarity at high energy via the $W^{+}{W}^{-}$ production at the LHC and future colliders
• Test of lepton flavour universality in $W$-boson decays into electrons and $\tau$-leptons using $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector
• Searching for single production of vectorlike quarks decaying into Wb at a future muon-proton collider
• Complete one-loop QED corrections to $D_s^{+}$ leptonic decays and impact on the CKM unitarity test
• Aligned Zee-Grimus-Neufeld model for $(g-2{)}_{\mu }$
• Global Determination of $|V_{us}|$