Regular Article – Theoretical Physics
Radiative decays of charged leptons as constraints of unitarity polygons for active-sterile neutrino mixing and CP violation
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
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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