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

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 σ, depending on the theoreti...

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Autores principales: Crivellin, Andreas, Kirk, Fiona, Manzari, Claudio Andrea, Montull, Marc
Lenguaje:eng
Publicado: 2020
Materias:
Acceso en línea:https://dx.doi.org/10.1007/JHEP12(2020)166
http://cds.cern.ch/record/2727098
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author Crivellin, Andreas
Kirk, Fiona
Manzari, Claudio Andrea
Montull, Marc
author_facet Crivellin, Andreas
Kirk, Fiona
Manzari, Claudio Andrea
Montull, Marc
author_sort Crivellin, Andreas
collection CERN
description 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 σ, 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 Wℓν couplings at tree-level, such that this modification can have the dominant phenomenological impact. In order to consistently assess agreement 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 Σ$_{1}$ 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 σ with respect to the begin.
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language eng
publishDate 2020
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spelling cern-27270982021-11-13T12:53:39Zdoi:10.1007/JHEP12(2020)166http://cds.cern.ch/record/2727098engCrivellin, AndreasKirk, FionaManzari, Claudio AndreaMontull, MarcGlobal Electroweak Fit and Vector-Like Leptons in Light of the Cabibbo Angle Anomalyhep-latParticle Physics - Latticehep-exParticle Physics - Experimenthep-phParticle Physics - PhenomenologyThe “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 σ, 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 Wℓν couplings at tree-level, such that this modification can have the dominant phenomenological impact. In order to consistently assess agreement 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 Σ$_{1}$ 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 σ with respect to the begin.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:2008.01113CERN-TH-2020-128PSI-PR-20-11UZ-TH 26/20oai:cds.cern.ch:27270982020-08-03
spellingShingle hep-lat
Particle Physics - Lattice
hep-ex
Particle Physics - Experiment
hep-ph
Particle Physics - Phenomenology
Crivellin, Andreas
Kirk, Fiona
Manzari, Claudio Andrea
Montull, Marc
Global Electroweak Fit and Vector-Like Leptons in Light of the Cabibbo Angle Anomaly
title Global Electroweak Fit and Vector-Like Leptons in Light of the Cabibbo Angle Anomaly
title_full Global Electroweak Fit and Vector-Like Leptons in Light of the Cabibbo Angle Anomaly
title_fullStr Global Electroweak Fit and Vector-Like Leptons in Light of the Cabibbo Angle Anomaly
title_full_unstemmed Global Electroweak Fit and Vector-Like Leptons in Light of the Cabibbo Angle Anomaly
title_short Global Electroweak Fit and Vector-Like Leptons in Light of the Cabibbo Angle Anomaly
title_sort global electroweak fit and vector-like leptons in light of the cabibbo angle anomaly
topic hep-lat
Particle Physics - Lattice
hep-ex
Particle Physics - Experiment
hep-ph
Particle Physics - Phenomenology
url https://dx.doi.org/10.1007/JHEP12(2020)166
http://cds.cern.ch/record/2727098
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