English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The "Cabibbo Angle Anomaly" (CAA) originates from the disagreement betweenthe CKM elements $V_{ud}$ and $V_{us}$ extracted from superallowed beta andkaon decays, respectively, once compared via CKM unitarity. It points towardsnew physics with a significance of up to $4\,\sigma$, depending on thetheoretical input used, and can be explained through modified $W$ couplings toleptons. In this context, vector-like leptons (VLLs) are prime candidates for acorresponding UV completion since they can affect $W\ell\nu$ couplings attree-level, such that this modification can have the dominant phenomenologicalimpact. In order to consistently asses the agreement with the data, a globalfit is necessary which we perform for gauge-invariant dimension-6 operators andall patterns obtained for the six possible representations (under the SM gaugegroup) 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 theelectroweak fit has a relevant impact, shifting the best fit pointsignificantly. Concerning the VLLs we discuss the bounds from charged leptonflavour violating processes and observe that a single representation cannotdescribe experimental data significantly better than the SM hypothesis.However, allowing for several representations of VLLs at the same time, we findthat 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 therest of the electroweak fit in such a way that its best fit point is preferredby more than $4\,\sigma$ with respect to the SM.

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