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|As Contributors:||Gerardo Hernández-Tomé|
|Submitted by:||Hernández-Tomé, Gerardo|
|Submitted to:||SciPost Physics Proceedings|
|Subject area:||Quantum Physics|
The flavor violating leptonic decays of the $\tau$ and $\mu$ leptons into three lighter charged leptons are revisited in the framework the Standard Model with massive neutrinos. In contrast to the previous prediction, we have found strongly suppressed rates for the $\tau^-\to \mu^- \ell^+ \ell^-$ ($\ell=\mu, e$) decays. Our results are in good agreement with the approximation of neglecting masses and momenta of the external particles in the loop integrals made in the first computation for the $\mu^- \to e^-e^+ e^-$ decay.
This contribution reports on a recalculation of all the processes of the kind L− → l−l′−l′+ within the Standard Model with massive neutrinos. Main aim of this calculation is to verify the claim in ref.  of BR(τ− → μ−l+l−) ≥ 10−14 within the same model. Ref.  calculates this process by performing an expansion around the momentum transfer q^2 = 0. This contribution points out that, being q^2 much larger than the neutrino mass squared, the expansion in ref.  amounts to evaluating the amplitude outside the physical region.
The main results of this contributions are summarized in table 2, confirming that, due to the smallness of the (m_neutrino / m_W)^4 ratio, all processes of the kind L− → l−l′−l′+ are hopelessly small within the SM, and any measurement would be a clear sign of new physics.
Before accepting the contribution, I would like to ask whether the relevant paper, ref. , has meanwhile been published in a journal.