Mounting Evidence for the Violation of Lepton Flavor Universality

TL;DR

Recent experimental anomalies suggest violations of lepton flavor universality, indicating potential new physics beyond the Standard Model, which future measurements could confirm and help extend our understanding of fundamental particles.

Contribution

The paper reviews evidence for lepton flavor universality violation and discusses how new exotic particles could explain these anomalies, highlighting the need for future experimental tests.

Findings

Hints of lepton flavor universality violation in precision observables

Potential explanations involving new exotic particles

Future experiments could confirm physics beyond the Standard Model

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.