- Effective approach to lepton observables: The seesaw case doi link

Auteur(s): Coy R., Frigerio M.

(Article) Publié: Physical Review D, vol. 99 p.095040 (2019)
Texte intégral en Openaccess : arxiv

Ref HAL: hal-01949587_v1
Ref Arxiv: 1812.03165
DOI: 10.1103/PhysRevD.99.095040
WoS: WOS:000470859800009
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
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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.