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Journal of High Energy Physics 1302 (2013) 048
Tree-level lepton universality violation in the presence of sterile neutrinos: impact for $R_K$ and $R_\pi$
A. Abada1, D. Das1, A. M. Teixeira2, A. Vicente1, C. Weiland1
(2013)

We consider a tree-level enhancement to the violation of lepton flavour universality in light meson decays arising from modified $W \ell \nu$ couplings in the standard model minimally extended by sterile neutrinos. Due to the presence of additional mixings between the active (left-handed) neutrinos and the new sterile states, the deviation from unitarity of the leptonic mixing matrix intervening in charged currents might lead to a tree-level enhancement of $R_{P} = \Gamma (P \to e \nu) / \Gamma (P \to \mu \nu)$, with $P=K, \pi$. We illustrate these enhancements in the case of the inverse seesaw model, showing that one can saturate the current experimental bounds on $\Delta r_{K}$ (and $\Delta r_{\pi}$), while in agreement with the different experimental and observational constraints.
1:  LPT - Laboratoire de Physique Théorique d'Orsay
2:  LPC-CLERMONT - Laboratoire de Physique Corpusculaire de Clermont-Ferrand
Physics/High Energy Physics - Phenomenology
Fulltext link: 
http://fr.arXiv.org/abs/1211.3052