https://doi.org/10.1140/epjc/s10052-020-08697-y
Regular Article – Theoretical Physics
Radiative decays of charged leptons as constraints of unitarity polygons for active-sterile neutrino mixing and CP violation
1
Institute of High Energy Physics and School of Physical Sciences, University of Chinese Academy of Sciences, 100049, Beijing, China
2
Center of High Energy Physics, Peking University, 100871, Beijing, China
Received:
25
September
2020
Accepted:
20
November
2020
Published online:
8
December
2020
We calculate the rates of radiative 
decays for 
, 
and 
by taking the unitary gauge in the 
active-sterile neutrino mixing scheme, and make it clear that constraints on the unitarity of the 
Pontecorvo–Maki–Nakagawa–Sakata (PMNS) matrix U extracted from decays in the minimal unitarity violation scheme differ from those obtained in the canonical seesaw mechanism with n heavy Majorana neutrinos by a factor 5/3. In such a natural seesaw case we show that the rates of can be used to cleanly and strongly constrain the effective apex of a unitarity polygon, and compare its geometry with the geometry of its three sub-triangles formed by two vectors 
and 
(for 
) in the complex plane. We find that the areas of such sub-triangles can be described in terms of the Jarlskog-like invariants of CP violation 
, and their small differences signify slight unitarity violation of the PMNS matrix U.
© The Author(s) 2020
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