Exploring CP-violating heavy neutrino oscillations in rare tau decays at Belle II

In this work, we study the lepton number violating tau decays via two intermediate on-shell Majorana neutrinos N_j into two charged pions and a charged lepton τ^±→π^±N_j→π^±π^±ℓ^∓. We consider the scenario where the heavy neutrino masses are within 0.5 GeV≤M_N≤1.5 GeV. We evaluated the possibility to measure the modulation of the decay width along the detector length for these processes at tau factories, such as Belle II. We study some realistic conditions which could lead to the observation of this phenomenon at futures τ factories.