HNLs from Heavy ALP decays at Neutrino Facilities

We present a chiral non-abelian dark sector model that features a spontaneous $SU(3)\times SU(2) \rightarrow SU(3)$ symmetry breaking and results in the formation of dark mesons, $\pi_D$, and baryons. The absence of a gauged $U(1)$ symmetry allows the dark baryons to potentially serve as dark matter candidates. The model incorporates HNLs and explores scenarios with enhanced active-to-sterile neutrino mixing. We analyze the mixing between the dark meson $\pi_D$ and the SM mesons $\pi^0$ and $\eta$. Utilizing this mixing and the $\pi^0$ flux at neutrino facilities, we investigate the decay of $\pi_D$ into pairs of HNLs, $\nu_D$. This study presents a novel approach where the $\nu_D$ emerges directly from the $\pi^0$ decay, providing distinct kinematic distributions compared to conventional neutrino mixing studies. Our investigation includes the DUNE and ICARUS near detectors, as well as stopped pion facilities and FASER$\nu$. Additionally, we consider the atmospheric $\pi^0$ flux for $\nu_D$ production, offering intriguing possibilities for the DUNE far detector.