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NLO prediction for the decays $\tau \to \ell \ell'\ell' \nu \bar \nu$ and $\mu \to e e e \nu \bar\nu$

by Matteo Fael

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Submission summary

Authors (as registered SciPost users): Matteo Fael
Submission information
Preprint Link: scipost_201811_00002v1  (pdf)
Date accepted: 2019-01-10
Date submitted: 2018-11-03 01:00
Submitted by: Fael, Matteo
Submitted to: SciPost Physics Proceedings
Proceedings issue: The 15th International Workshop on Tau Lepton Physics (TAU2018)
Ontological classification
Academic field: Physics
  • High-Energy Physics - Phenomenology
Approaches: Experimental, Theoretical


These proceedings present the differential decay rates and the branching ratios of the tau and muon decays $\tau \to \ell \ell' \ell' \nu \bar\nu$ (with $\ell,\ell'=\mu,e$) and $\mu \to e e e \nu \bar \nu$ in the Standard Model at NLO. These five-body leptonic decays are a tool to study the Lorentz structure of weak interactions and to test lepton flavour universality. They are also a source of SM background to searches for the lepton-flavour-violating decays $\mu \to e e e$ and $\tau \to \ell \ell' \ell'$. Even if the shift in the branching ratios induced by radiative corrections turns out to be small and of order 1% - mainly due to a running effect of the fine structure constant - locally in the phase space these corrections can reach the 5 - 10% level, depending on the applied cuts. We found for instance that in the phase space region where the neutrino energies are small, and the momenta of the three charged leptons have a similar signature as in $\mu \to eee$ and $\tau \to \ell \ell'\ell'$, the NLO corrections decrease the leading-order prediction by about 10 - 20%.

Published as SciPost Phys. Proc. 1, 009 (2019)

Reports on this Submission

Anonymous Report 1 on 2018-12-12 (Invited Report)


The conference contribution under consideration is entirely based on the reviewed journal publication JHEP 01 (2017) 84. It is well written and clear. Hence, in my opinion there is no need for a more detailed report.

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