https://doi.org/10.1140/epjc/s10052-021-09618-3
Regular Article - Theoretical Physics
The LFU ratio 
in the Standard Model and beyond
1
Theoretische Physik 1, Naturwissenschaftlich-Technische Fakultät, Universität Siegen, Walter-Flex-Straße 3, 57068, Siegen, Germany
2
Dipartimento di Fisica, Università di Torino & INFN, Sezione di Torino, 10125, Turin, Italy
3
Physik-Institut, Universität Zürich, 8057, Zurich, Switzerland
4
Physik Department T31, Technische Universität München, James-Franck-Straße 1, 85748, Garching, Germany
Received:
7
February
2021
Accepted:
28
August
2021
Published online:
25
September
2021
We discuss the possibility of performing precise tests of 
universality in 
decays. We show that in wide regions of the dilepton invariant mass spectrum the ratio between muonic and electronic decay widths can be predicted with high accuracy, both within and beyond the Standard Model. We present numerical expressions which can be used to extract precise information on short-distance dynamics if a deviation from universality is observed in the data.
© The Author(s) 2021
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