Global Electroweak Fit and Vector-Like Leptons in Light of the Cabibbo Angle Anomaly

Abstract

The "Cabibbo Angle Anomaly" (CAA) originates from the disagreement between the CKM elements $V_{ud}$ and $V_{us}$ extracted from superallowed beta and kaon decays, respectively, once compared via CKM unitarity. It points towards new physics with a significance of up to $4\sigma$, depending on the theoretical input used, and can be explained through modified $W$ couplings to leptons. In this context, vector-like leptons (VLLs) are prime candidates for a corresponding UV completion since they can affect $W\ell \nu$ couplings at tree-level, such that this modification can have the dominant phenomenological impact. In order to consistently asses the agreement with the data, a global fit is necessary which we perform for gauge-invariant dimension-6 operators and all patterns obtained for the six possible representations (under the SM gauge group) of VLLs. We find that even in the lepton flavour universal case, including the measurements of the CKM elements $V_{us}$ and $V_{ud}$ into the electroweak fit has a relevant impact, shifting the best fit point significantly. Concerning the VLLs we discuss the bounds from charged lepton flavour violating processes and observe that a single representation cannot describe experimental data significantly better than the SM hypothesis. However, allowing for several representations of VLLs at the same time, we find that the simple scenario in which $N$ couples to electrons via the Higgs and ${\Sigma }_1$ couples to muons not only explains the CAA but also improves the rest of the electroweak fit in such a way that its best fit point is preferred by more than $4\sigma$ with respect to the SM.

arXiv commentVersion accepted for publication in JHEP, 34 pages, 9 figures, 7 tables, typos corrected

References in corpus (6)

• FLAG Review 2019
• Little Higgs Models and Their Phenomenology
• Precision Tau Physics
• Probing seesaw at LHC
• A Tale of Two Anomalies
• Effective approach to lepton observables: the seesaw case

Cited by in corpus (72)

• Top, Higgs, Diboson and Electroweak Fit to the Standard Model Effective Field Theory
• Consequences of chirally enhanced explanations of $(g-2{)}_{\mu }$ for $h\to \mu \mu$ and $Z\to \mu \mu$
• Correlating $h\to {\mu }^{+}{\mu }^{-}$ to the Anomalous Magnetic Moment of the Muon via Leptoquarks
• The Fermi constant from muon decay versus electroweak fits and CKM unitarity
• Combined Constraints on First Generation Leptoquarks
• Searching for Lepton Flavour (Universality) Violation and Collider Signals from a Singly-Charged Scalar Singlet
• Are the CKM anomalies induced by vector-like quarks? Limits from flavor changing and Standard Model precision tests
• Vector-like Singlet Quarks: a Roadmap
• First-Generation New Physics in Simplified Models: From Low-Energy Parity Violation to the LHC
• Addressing the CKM Unitarity Problem with a Vector-like Up Quark
• Unveiling Hidden Physics at the LHC
• Global Analysis of Leptophilic Z' Bosons
• Multi-lepton signatures of vector-like leptons with flavor
• Combined Explanation of the $Z\to b\bar{b}$ Forward-Backward Asymmetry, the Cabibbo Angle Anomaly, $\tau \to \mu \nu \nu$ and $b\to s{\ell }^{+}{\ell }^{-}$ Data
• Anomalies in Particle Physics
• Muon $g-2$ in two Higgs doublet models with vectorlike leptons
• Global Fit of Modified Quark Couplings to EW Gauge Bosons and Vector-Like Quarks in Light of the Cabibbo Angle Anomaly
• New leptons with exotic decays: collider limits and dark matter complementarity
• Testing Lepton Flavor Universality with Pion, Kaon, Tau, and Beta Decays
• Update on $|V_{us}|$ and $|V_{us}/V_{ud}|$ from semileptonic kaon and pion decays
• The Importance of Flavor in SMEFT Electroweak Precision Fits
• Beta-decay implications for the W-boson mass anomaly
• Leptonic anomalous magnetic moments in $\nu$SMEFT
• Ab-initio electroweak corrections to superallowed $\beta$ decays and their impact on $V_{ud}$
• An $\text{ab initio}$ strategy for taming nuclear-structure dependence of $V_{ud}$ extractions: the ${}^{10}\mathrm{C}\to {}^{10}\mathrm{B}$ superallowed transition
• Radiative corrections to superallowed $\beta$ decays in effective field theory
• Radiative corrections to semileptonic beta decays: Progress and challenges
• All orders factorization and the Coulomb problem
• A bridge to new physics: proposing new -- and reviving old -- explanations of $a_{\mu }$
• Correlating Non-Resonant Di-Electron Searches at the LHC to the Cabibbo-Angle Anomaly and Lepton Flavour Universality Violation
• New physics interpretation of $W$-boson mass anomaly
• Tau-jet signatures of vectorlike quark decays to heavy charged and neutral Higgs bosons
• Field Theory of the Fermi Function
• Sterile neutrinos with non-standard interactions in $\beta$- and $0\nu \beta \beta$-decay experiments
• Comprehensive Analysis of Charged Lepton Flavour Violation in the Symmetry Protected Type-I Seesaw
• $W$ mass in a model with vector-like leptons and $U(1{)}^{\prime }$
• The Singly-Charged Scalar Singlet as the Origin of Neutrino Masses
• One colorful resolution to the neutrino mass generation, three lepton flavor universality anomalies, and the Cabibbo angle anomaly
• Collider signatures of vector-like fermions from a flavor symmetric model
• Light scalars within the $\mathcal{C}\mathcal{P}$-conserving Aligned-two-Higgs-doublet model
• Addendum to: Combined Constraints on First Generation Leptoquarks
• Probing Heavy Neutrino Magnetic Moments at the LHC using Long-Lived Particle Searches
• Minimal model for the $W$-boson mass, $(g-2{)}_{\mu }$, $h\to {\mu }^{+}{\mu }^{-}$ and quark-mixing-matrix unitarity
• Next-to-Leading-Order QCD Matching for $\Delta F=2$ Processes in Scalar Leptoquark Models
• Current status on pair-produced muon-philic vectorlike leptons in multilepton channels at the LHC
• Renormalization of beta decay at three loops and beyond
• Relic Challenges for Vector-Like Fermions as Connectors to a Dark Sector
• The Muon Magnetic Moment and Physics Beyond the Standard Model
• Predictions for Muon Electric and Magnetic Dipole Moments from $h\to {\mu }^{+}{\mu }^{-}$ in Two-Higgs-Doublet Models with New Leptons
• Global analysis and LHC study of a vector-like extension of the Standard Model with extra scalars
• Effective Field Theory of Chirally-Enhanced Muon Mass and Dipole Operators
• Leptonic CP violation from a vector-like lepton
• Investigation of $(g-2{)}_{\mu }$ anomaly in the $\mu$-specific 2HDM with Vector like leptons and the phenomenological implications
• A radiatively induced inverse seesaw model with hidden $U(1)$ gauge symmetry
• The Two Scales of New Physics in Higgs Couplings
• $Z$ mediated Flavour Changing Neutral Currents with a Fourth Vector-Like Family
• Search for vector-like leptons coupling to first- and second-generation Standard Model leptons in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector
• Gauging lepton flavor SU(3) for the muon $g-2$
• Custodial Symmetry (Violation) in SMEFT
• Theoretical point of view on Cabibbo angle anomaly
• MeV Sterile Neutrino in light of the Cabibbo-Angle Anomaly
• Excited lepton triplet contribution to electroweak observables at one loop level
• Vector-like quark doublets, weak-basis invariants and CP violation
• Collider imprint of vector-like leptons in light of anomalous magnetic moment and neutrino data
• Exploring the Null Results in the Direct Detection Experiments, $(g-2{)}_{\ell }$ and Neutrino Mass in an Extended $U(1{)}_{L_{\mu }-L_{\tau }}$ Model Constrained through the $Z\to {\ell }^{+}{\ell }^{-}$ Decays
• Deep Learning Searches for Vector-Like Leptons at the LHC and Electron/Muon Colliders
• Round table on Standard Model Anomalies
• Electron Mass Singularities in Semileptonic Kaon Decays
• Complete one-loop QED corrections to $D_s^{+}$ leptonic decays and impact on the CKM unitarity test
• Graph Reinforcement Learning for Exploring BSM Model Spaces
• Pion $\beta$ decay and $\tau \to \pi \pi {\nu }_{\tau }$ beyond leading logarithms
• From Higgs physics to lepton flavour violation: current bounds and future prospects for vector-like lepton models