And there was another conundrum, thanks to results from Los Alamos’ LSND experiment and Fermilab’s MiniBooNE (MicroBooNE’s predecessor). Both found evidence of muon neutrinos oscillating into electron neutrinos in a way that shouldn’t be possible if there were just three neutrino flavors. So physicists suggested there might be a fourth flavor: the sterile neutrino, so named because unlike the other three, it does not couple to a charged counterpart via the electroweak force.