Researchers from the KM3NeT collaboration analyzed 5,828 atmospheric neutrino events detected by a telescope in the Mediterranean Sea to test whether the laws of physics remain constant everywhere in the universe, a principle called Lorentz invariance that underlies Einstein's theory of relativity.
The team found no evidence that Lorentz invariance was violated. However, they set new experimental limits on how large any such violations could be without contradicting their observations. The results included the first direct constraints on possible differences in how muon and tau neutrinos behave. Results appear in the Journal of Cosmology and Astroparticle Physics.
Some theories attempting to merge gravity with quantum physics suggest Lorentz invariance might not always hold. Testing this requires examining whether spacetime is continuous or made of discrete units, according to Alba Domi, a researcher at Erlangen Centre for Astroparticle Physics and a corresponding author on the study.
Neutrinos serve as effective probes for this question because they travel vast distances through matter and can oscillate between different types as they move. The probability of these transformations can be predicted precisely. If observations deviate from predictions, it could signal new physics including Lorentz invariance violations.
The researchers analyzed 1.4 years of data from KM3NeT/ORCA's first six detection units, comparing observed neutrino energies and arrival directions against theoretical predictions. Their results proved competitive with longer-running experiments like IceCube and Super-Kamiokande, despite using an early, partial detector configuration.
Lukas Hennig, a Ph.D. student at ECAP and the study's other corresponding author, noted that future analyses with more data and a fully expanded detector will enable searches for even smaller effects. The team also plans to extend investigations to KM3NeT/ARCA, which detects higher-energy neutrinos from distant astrophysical sources that could reveal effects of Lorentz invariance violation more clearly over long distances.