“…In more generic context including the ξ bound, we expect that the better constraints which improve the current ones [37,43,44] 4 will be obtained before DUNE starts to do τ neutrino physics. It will be done, for example, by the ongoing and upcoming experiments such as SBN program at Fermilab [33], JSNS2 [34], T2K [18], NOvA [19], Super-K [45], IceCube [46,47], KM3NeT [48], JUNO [36,49], and possibly Hyper-K [13]. These are the case of low-scale unitarity violation (or low mass sterile leptons) and the bound is much severer in high-scale unitarity violation case < ∼ 10 −3 [37].…”