Mounting Evidence for the Violation of Lepton Flavor Universality

Abstract

The Standard Model (SM) of particle physics was finalized in its current form in the mid-1970s, and has been extensively tested and confirmed ever since, with the discovery of the Higgs boson in 2012 being the last missing piece. While no new particles have been directly discovered at the Large Hadron Collider (LHC) at CERN so far, precision observables sensitive to quantum effects of new particles have accumulated intriguing hints for physics beyond the SM. All these anomalies can be interpreted from the point of view of lepton flavor universality, i.e., as hints that electrons, muons, and tau leptons differ much more than predicted by the SM. These tensions can be explained by postulating the existence of new exotic particles. Future measurements will be able to conclusively test this hypothesis, potentially providing long-awaited evidence how the SM needs to be extended at high energies.

7 pages, 1 figure; published as "Science Perspective," addressed to general audience

References in corpus (5)

• Measurement of the Positive Muon Anomalous Magnetic Moment to 0.46 ppm
• Angular Distributions of B -> K ll Decays
• Search for resonant and nonresonant new phenomena in high-mass dilepton final states at $\sqrt{s}=$ 13 TeV
• Consequences of chirally enhanced explanations of $(g-2{)}_{\mu }$ for $h\to \mu \mu$ and $Z\to \mu \mu$
• Lepton-flavour non-universality of $\bar{B}\to D^{\ast }\ell \bar{\nu }$ angular distributions in and beyond the Standard Model

Cited by in corpus (30)

• Constraints on Lepton Universality Violation from Rare $B$ Decays
• Scrutinizing CKM unitarity with a new measurement of the $K_{\mu 3}/K_{\mu 2}$ branching fraction
• Muon $g-2$: A review
• Impact of ${\Lambda }_b\to {\Lambda }_c\tau \nu$ measurement on New Physics in $b\to cl\nu$ transitions
• Global Fit of Modified Quark Couplings to EW Gauge Bosons and Vector-Like Quarks in Light of the Cabibbo Angle Anomaly
• Towards testing the magnetic moment of the tau at one part per million
• Testing Lepton Flavor Universality with Pion, Kaon, Tau, and Beta Decays
• Ab-initio electroweak corrections to superallowed $\beta$ decays and their impact on $V_{ud}$
• Unified Explanation of the Anomalies in Semi-Leptonic $B$ decays and the $W$ Mass
• Radiative corrections to superallowed $\beta$ decays in effective field theory
• Determination of $|V_{cb}|$ using ${\overline{B}}^0\to D^{\ast +}{\ell }^{-}{\bar{\nu }}_{\ell }$ decays with Belle II
• Width effects of broad new resonances in loop observables and application to $(g-2{)}_{\mu }$
• Towards excluding a light $Z^{\prime }$ explanation of $b\to s{\ell }^{+}{\ell }^{-}$
• Anomalous thresholds in $B\to (P,V){\gamma }^{\ast }$ form factors
• Consistency and Interpretation of the LHC (Di-)Di-Jet Excesses
• Virtual Photon Emission in Leptonic Decays of Charged Pseudoscalar Mesons
• Diquark Explanation of $b\to s{\ell }^{+}{\ell }^{-}$
• The Muon Magnetic Moment and Physics Beyond the Standard Model
• Dark SU(2) Stueckelberg portal
• Probing the muon (g-2) anomaly at the LHC in final states with two muons and two taus
• Hyperon production in quasielastic ${\bar{\nu }}_{\tau }-$nucleon scattering
• The Radiative Flavor Template at the LHC: Lepton non-universality and g-2
• A fermionic portal to a non-abelian dark sector
• Addressing the $R_{\tau /\mu ,e}\left(D^{(\ast )}\right)$ puzzle through New Physics four-fermion operators and their impact on ${\Lambda }_b\to {\Lambda }_c\tau {\bar{\nu }}_{\tau }$ decay
• A two-generational $\mathrm{SU}(7)$ model with extended weak sector: mass hierarchies, mixings, and the flavor non-universality
• The Angular Observables of ${\Lambda }_b\to {\Lambda }_c(\to {\Lambda }^0{\pi }^{+}){\tau }^{-}(\to {\pi }^{-}{\nu }_{\tau }){\bar{\nu }}_{\tau }$ within the Paradigm of FCCC Anomalies
• Experimental test of the third quantization of the electromagnetic field
• Pion $\beta$ decay and $\tau \to \pi \pi {\nu }_{\tau }$ beyond leading logarithms
• Explaining lepton-flavor non-universality and self-interacting dark matter with $L_{\mu }-L_{\tau }$
• Explaining the hints for lepton flavour universality violation with three $S_2$ leptoquark generations