Orateur
Description
The $B\to K \nu \nu$ decays are among the cleanest rare processes in the Standard Model (SM), as they are dominated by short-distance contributions. Recently, the Belle-II experiment has observed this process for the first time, with a branching ratio that lies $\approx 3\sigma$ above its SM prediction. Such deviation can be consistently accommodated in an Effective Field Theory (EFT) scenario with operators made with SM neutrinos. At dimension-six, the relevant operators simply rescale the SM branching ratio, while higher-dimensional operators can modify the di-neutrino invariant-mass distribution. In this talk, we will show that the latter scenario generically induces sizable contributions to neutrino masses through Renormalization Group evolution, thus leading to severe fine-tuning problems. As an alternative, we consider an EFT with a light sterile neutrino, which avoid the fine-tuning issue in neutrino masses, while still leading to a potential distortion of the di-neutrino spectrum that can be tested experimentally at Belle-II.