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Modified lepton couplings and the Cabibbo-angle anomaly
High Energy Physics - Phenomenology · Submitted 8 Sep 2020
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim Therefore, we perform a model-independent Bayesian global analysis and find that non-zero modifications of electron and muon neutrino couplings are preferred at more than $99.99\%\,{\rm C.L.}$ (corresponding to more than $4\,\sigma$).
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The abstract, sentence by sentence
Significant discrepancies between the different determinations of the Cabibbo angle have been observed. Here, we point out that this "Cabibbo-angle anomaly" can be explained by lepton flavour universality (LFU) violating New Physics (NP) in the neutrino sector. However, modified neutrino couplings to Standard Model gauge bosons also affect many other observables sensitive to LFU violation, which have to be taken into account in order to assess the viability of this explanation. Therefore, we perform a model-independent Bayesian global analysis and find that non-zero modifications of electron and muon neutrino couplings are preferred at more than $99.99\%\,{\rm C.L.}$ (corresponding to more than $4\,\sigma$). Our results show that constructive effects in the muon sector are necessary, meaning simple models with right-handed neutrinos are discarded and more sophisticated NP models required.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | Significant discrepancies between the different determinations of the Cabibbo angle have been observed. | background 1.00 | 0.09 | 0.02 | asserted 1.00 |
| s1 | Here, we point out that this "Cabibbo-angle anomaly" can be explained by lepton flavour universality (LFU) violating New Physics (NP) in the neutrino sector. | contribution 0.66 | 0.77 | 0.25 | asserted 0.57 |
| s2 | However, modified neutrino couplings to Standard Model gauge bosons also affect many other observables sensitive to LFU violation, which have to be taken into account in order to assess the viability of this explanation. | background 0.40 | 0.10 | 0.04 | asserted 0.97 |
| s3 | Therefore, we perform a model-independent Bayesian global analysis and find that non-zero modifications of electron and muon neutrino couplings are preferred at more than $99.99\%\,{\rm C.L.}$ (corresponding to more than $4\,\sigma$). | result 1.00 | 0.97 | 0.76 | asserted 1.00 |
| s4 | Our results show that constructive effects in the muon sector are necessary, meaning simple models with right-handed neutrinos are discarded and more sophisticated NP models required. | interpretation 0.98 | 0.91 | 0.33 | asserted 1.00 |
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The paper
Original abstract
Significant discrepancies between the different determinations of the Cabibbo angle have been observed. Here, we point out that this "Cabibbo-angle anomaly" can be explained by lepton flavour universality (LFU) violating New Physics (NP) in the neutrino sector. However, modified neutrino couplings to Standard Model gauge bosons also affect many other observables sensitive to LFU violation, which have to be taken into account in order to assess the viability of this explanation. Therefore, we perform a model-independent Bayesian global analysis and find that non-zero modifications of electron and muon neutrino couplings are preferred at more than $99.99\%\,{\rm C.L.}$ (corresponding to more than $4\,\sigma$). Our results show that constructive effects in the muon sector are necessary, meaning simple models with right-handed neutrinos are discarded and more sophisticated NP models required.
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References
How the literature uses it
15 arXiv papers cite this in 17 sentences
Papers citing it · 11 sentences without a confident label
Cites it as background 6 papers
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In addition, there is the deficit in first row CKM unitarity, known as the Cabibbo Angle Anomaly (CAA) [ref] which has been recently studied as a possible sign of LFU violation [ref] and lepton flavour violation (LFV) [ref] opening the road for interesting connections to other anomalies in the flavour sector, such as $Z→b̅b$ [ref] , $τ→μνν$ [ref] , the aforementioned $b→sℓℓ$ [ref] and the recent CMS observations in dilepton final state searches [ref] .
Vector-like Leptons in Light of the Cabibbo-Angle Anomaly · Introduction · 0.83
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Various models that include mediators at the TeV scale have been suggested as possible solutions to CAA1 [ref] .
The remarkable role of the vector-like quark doublet in the Cabibbo angle and $W$-mass anomalies · Introduction · 0.94
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The observed deficit in first row CKM unitarity, known as the Cabibbo Angle Anomaly (CAA) [ref] , is among the most intriguing deviation from the Standard Model (SM) predictions.
Explaining the Cabibbo Angle Anomaly · Introduction · 0.86
What it cites · 21 sentences without a confident label
Contests 7 papers
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This result shows that current data clearly favours the NP hypothesis, exclude conventional models with right-handed neutrinos leading to necessary destructive interference [ref] and promote the search for NP models as the ones presented in Refs. [ref] .
Radiatively Induced Neutrino Masses and Large Higgs-Neutrino Couplings in the Standard Model with Majorana Fields · Results and Conclusions · contest 0.73
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This result shows that current data clearly favours the NP hypothesis, exclude conventional models with right-handed neutrinos leading to necessary destructive interference [ref] and promote the search for NP models as the ones presented in Refs. [ref] .
Minimal Radiative Neutrino Mass Mechanism for Inverse Seesaw Models · Results and Conclusions · contest 0.73
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This result shows that current data clearly favours the NP hypothesis, exclude conventional models with right-handed neutrinos leading to necessary destructive interference [ref] and promote the search for NP models as the ones presented in Refs. [ref] .
Non-unitarity of the leptonic mixing matrix: Present bounds and future sensitivities · Results and Conclusions · contest 0.73
Uses the method or tool of 2 papers
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Our analysis is performed in a Bayesian framework using the package [ref] .
$\texttt{HEPfit}$: a Code for the Combination of Indirect and Direct Constraints on High Energy Physics Models · Results and Conclusions · 1.00
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For a more direct model comparison between the NP hypothesis and the SM we look at values of the Information Criterion (IC) [ref] , a quantity characterized by an estimate of the predictive accuracy of the fitted model [ref] and a penalty factor for its number of free parameters.
Understanding predictive information criteria for Bayesian models · Results and Conclusions · 0.87
Uses data or values from 11 papers
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Among these parameters, only the determination of the latter [ref] (which is determined with a very high precision from the muon lifetime) is affected by the modification of the neutrino couplings in Eq. [ref].
Measurement of the Positive Muon Lifetime and Determination of the Fermi Constant to Part-per-Million Precision · Setup · 0.95
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Here, we have ratios of W decays [ref] ($W→ℓ_iν_i /W→ℓ_jν_j$) where we included the latest ATLAS results [ref] , as well as of Kaon [ref] , pion [ref] and tau decays (see Ref. [ref] for a recent overview).
Precision Measurement of the Ratio of the Charged Kaon Leptonic Decay Rates · Setup · 0.97
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Here, we have ratios of W decays [ref] ($W→ℓ_iν_i /W→ℓ_jν_j$) where we included the latest ATLAS results [ref] , as well as of Kaon [ref] , pion [ref] and tau decays (see Ref. [ref] for a recent overview).
Test of the universality of $\tau$ and $\mu$ lepton couplings in $W$-boson decays from $t\bar{t}$ events with the ATLAS detector · Setup · 0.97
Cites as background 8 papers
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This anomaly was studied in the scenario of first row CKM unitarity violation [ref] , however it is challenging to explain it in this context due other flavour bounds, like Kaon or $B_d-B̅_d$ mixing [ref] .
Patterns of Flavour Violation in Models with Vector-Like Quarks · Introduction · 0.81
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This anomaly was studied in the scenario of first row CKM unitarity violation [ref] , however it is challenging to explain it in this context due other flavour bounds, like Kaon or $B_d-B̅_d$ mixing [ref] .
The CKM unitarity problem: A trace of new physics at the TeV scale? · Introduction · 0.81
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This anomaly was studied in the scenario of first row CKM unitarity violation [ref] , however it is challenging to explain it in this context due other flavour bounds, like Kaon or $B_d-B̅_d$ mixing [ref] .
Vector-like Quark Interpretation for the CKM Unitarity Violation, Excess in Higgs Signal Strength, and Bottom Quark Forward-Backward Asymmetry · Introduction · 0.81
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