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Title: U(2)⁵ flavor symmetry and lepton universality violation in W→τν̄τ

The seeming violation of universality in the τ lepton coupling to the W boson suggested by LEP-II data is studied using an effective field theory (EFT) approach. Within this framework we explore how this feature fits into the current constraints from electroweak precision observables using different assumptions about the flavor structure of New Physics, namely [U(2)×U(1)]⁵ and U(2)⁵. We show the importance of leptonic and semileptonic tau decay measurements, giving 3–4 TeV bounds on the New Physics effective scale at 90% C.L. We conclude under very general assumptions that it is not possible to accommodate this deviation from universality in the EFT framework, and thus such a signal could only be explained by the introduction of light degrees of freedom or New Physics strongly coupled at the electroweak scale.
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Publication Date:
Publisher's Accepted Manuscript
Journal Name:
Physical Review. D, Particles, Fields, Gravitation and Cosmology
Additional Journal Information:
Journal Volume: 85; Journal Issue: 11; Related Information: CHORUS Timestamp: 2017-04-06 11:28:21; Journal ID: ISSN 1550-7998
American Physical Society
Sponsoring Org:
Country of Publication:
United States
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1103652