Could quantum gravity slow down neutrinos?

In addition to its implications for astrophysics, the hunt for neutrinos originating from gamma-ray bursts could also be significant in quantum-gravity research, as they are excellent probes of the microscopic fabric of spacetime. Some previous studies based on neutrinos observed by the IceCube observatory found intriguing preliminary evidence that some of them might be gamma-ray burst neutrinos whose travel times are affected by quantum properties of spacetime that would slow down some of the neutrinos while speeding up others. The IceCube collaboration recently significantly revised the estimates of the direction of observation of their neutrinos, and we here investigate how the corrected directional information affects the results of the previous quantum-spacetime-inspired analyses. We find that there is now little evidence for neutrinos being sped up by quantum spacetime properties, whereas the evidence for neutrinos being slowed down by quantum spacetime is even stronger than previously determined. Our most conservative estimates find a false-alarm probability of less than 1% for these ‘slow neutrinos’, providing motivation for future studies on larger data samples. Following a recalibration of the direction and energy of neutrinos detected by IceCube, a reanalysis using a quantum-gravity model finds stronger evidence for subluminal neutrinos from gamma-ray bursts, which are slowed down by quantum spacetime properties.