Leptoquark-mediated Dirac neutrino mass and its impact on $$ B\to K\nu \overline{\nu} $$ and $$ K\to \pi \nu \overline{\nu} $$ decays

Abstract Right-handed neutrinos ν R play a crucial role in flavor-changing neutral-current processes with missing energy, such as "Image missing" and "Image missing", where Belle-II reports unexpectedly large branching fraction in $$ B\to K\nu \overline{\nu} $$ B → Kν ν ¯ decays. Assuming ν R is the partner of the active neutrino ν L in the standard model, a Dirac-type neutrino framework emerges. We investigate a scenario of radiative Dirac neutrino mass generation in a scalar leptoquark (LQ) model with a global U(1) X symmetry to suppress Majorana mass, tree-level Dirac mass, and diquark couplings. The simplest LQ realization consists of two S 1 = (3, 1, −1/3) LQs with distinct U(1) X charges. A non-Casas-Ibarra parametrization is proposed to match neutrino data with fewer model parameters. Imposing current experimental constraints from meson mixing and lepton flavor-violating processes, we find that right-handed neutrino effects can significantly enhance $$ B\to {K}^{\left(\ast \right)}\nu \overline{\nu} $$ B → K ∗ ν ν ¯ and $$ {K}^{+}\to {\pi}^{+}\nu \overline{\nu} $$ K + → π + ν ν ¯ . Additionally, the model predicts excesses in R D from $$ B\to D\tau \overline{\nu} $$ B → Dτ ν ¯ that remain within 1σ of current experimental data.