Another test of the Lorentz invariance has been reported, and this time it is in the neutrino oscillation.
Neutrinos could be a sensitive probe of LV through their oscillation behavior. They are known to oscillate between three flavors (electron, muon, and tau), but Lorentz violations could cause additional oscillations that would modify how the signal depends on neutrino energy and path length (i.e., the distance a neutrino travels between creation and detection). Past searches have failed to find LV oscillations in reactor neutrinos. The Super-Kamiokande experiment—an underground neutrino observatory in Japan—has now reported a characterization of atmospheric neutrinos accessing much greater ranges in neutrino energy and path length than previous tests, giving it greater sensitivity to LV oscillations. The data showed no LV signature, allowing the researchers to place the first-ever limits on LV oscillations between muon and tau neutrinos. For other flavor oscillations, they improve on previous limits by factors of a thousand or more.