Eur. Phys. J. C (2012) 72: 2228
https://doi.org/10.1140/epjc/s10052-012-2228-2

Regular Article - Theoretical Physics

Revisiting the Γ(K→eν)/Γ(K→μν) ratio in supersymmetric unified models

¹ Centro de Física Teórica de Partículas, CFTP, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais 1, 1049-001, Lisboa, Portugal
² CNRS/IN2P3 – UMR 6533, Laboratoire de Physique Corpusculaire, Campus des Cézeaux, 24 Av. des Landais, 63171, Aubière Cedex, France

^* e-mail: jorge.romao@ist.utl.pt

Received: 25 May 2012
Revised: 31 October 2012
Published online: 20 November 2012

Abstract

It has been pointed out that supersymmetric extensions of the Standard Model can induce significant changes to the theoretical prediction of the ratio Γ(K→eν)/Γ(K→μν)≡R _K , through lepton flavour violating couplings. In this work we carry out a full computation of all one-loop corrections to the relevant νℓH ⁺ vertex, and discuss the new contributions to R _K arising in the context of different constrained (minimal supergravity-inspired) models which succeed in accounting for neutrino data, further considering the possibility of accommodating a near-future observation of a μ→eγ transition. We also re-evaluate the prospects for R _K in the framework of unconstrained supersymmetric models. In all cases, we address the question of whether it is possible to saturate the current experimental sensitivity on R _K while in agreement with the recent limits on B-meson decay observables (in particular BR(B _s →μ ⁺ μ ⁻) and BR(B _u →τν)), as well as BR(τ→eγ) and available collider constraints. Our findings reveal that in view of the recent bounds, and even when enhanced by effective sources of flavour violation in the right-handed sector, constrained supersymmetric (seesaw) models typically provide excessively small contributions to R _K . Larger contributions can be found in more general settings, where the charged Higgs mass can be effectively lowered, and even further enhanced in the unconstrained MSSM. However, our analysis clearly shows that even in this last case SUSY contributions to R _K are still unable to saturate the current experimental bounds on this observable, especially due to a strong tension with the B _u →τν bound.