Abstract
Abstract We consider a tree-level enhancement to the violation of lepton flavour universality in light meson decays arising from modified Wℓν 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 = Γ(P → eν)/Γ(P → μν), with P = K, π. We illustrate these enhancements in the case of the inverse seesaw model, showing that one can saturate the current experimental bounds on Δr K (and Δr π ), while in agreement with the different experimental and observational constraints.
Highlights
Whether or not RP can probe a model of NP naturally depends on the nature and on the expected size of the corresponding contributions to ∆rP
We consider a tree-level enhancement to the violation of lepton flavour universality in light meson decays arising from modified W lν couplings in the standard model minimally extended by sterile neutrinos
The existence of sterile neutrinos can potentially lead to a significant violation of lepton flavour universality at tree-level in light meson decays
Summary
There are strong experimental and observational bounds on the mass regimes and on the size of the active-sterile mixings that must be satisfied. There are robust laboratory bounds from direct sterile neutrinos searches [15, 25], since the latter can be produced in meson decays such as π± → μ±ν, with rates dependent on their mixing with the active neutrinos. Unless the active-sterile mixings are negligible, the modified W lν vertex may contribute to lepton flavour violation (LFV) processes, with potentially large rates. The generic idea explored in this work applies to any model where the active neutrinos have sizeable mixings with some additional singlet states, we consider the case of the Inverse Seesaw [22] to illustrate the potential of a model with sterile neutrinos regarding tree-level contributions to light meson decays. There are other possibilities [20, 21]
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