%0 Journal Article
%T Effective approach to lepton observables: The seesaw case
%+ Laboratoire Charles Coulomb (L2C)
%A Coy, Rupert
%A Frigerio, Michele
%< avec comité de lecture
%Z L2C:18-374
%@ 1550-7998
%J Physical Review D
%I American Physical Society
%V 99
%N 9
%P 095040
%8 2019-05-31
%D 2019
%Z 1812.03165
%R 10.1103/PhysRevD.99.095040
%Z Physics [physics]/High Energy Physics - Phenomenology [hep-ph]Journal articles
%X In the absence of direct evidence of new physics, any ultraviolet theory can be reduced to its specific set of low-energy effective operators. As a case study, we derive the effective field theory for the seesaw extension of the Standard Model, with sterile neutrinos of mass $M>m_W$. We systematically compute all Wilson coefficients generated at one loop. Hence, it becomes straightforward to (i) identify the seesaw parameters compatible with the smallness of neutrino masses; (ii) compute precision lepton observables, which may be sensitive to scales as large as $M\sim 10^3$ TeV; and (iii) establish sharp correlations among those observables. We find that the flavour-conserving Wilson coefficients set an upper bound on the flavour-violating ones. The low-energy limits on $\mu\to e$ and $\tau\to e,\mu$ transitions suppress flavour violation in $Z$ and Higgs decays, as well as electric dipole moments, far beyond the experimental reach. The bounds from the universality of $G_F$ and the invisible $Z$ width are more stringent than present and future limits on $\tau\to e,\mu$ transitions. We also present a general spurion analysis, to compare the seesaw with different models, thus assessing the discriminating potential of the effective approach.
%G English
%2 https://hal.science/hal-01949587/document
%2 https://hal.science/hal-01949587/file/PhysRevD.99.095040.pdf
%L hal-01949587
%U https://hal.science/hal-01949587
%~ CNRS
%~ L2C
%~ MIPS
%~ UNIV-MONTPELLIER
%~ AMIDEX
%~ ANR
%~ UM-2015-2021