Reacción a "Reactions to experiment using neutrinos to understand quantum gravity"

In this work, the IceCube collaboration searches for quantum gravity effects in the astrophysical neutrino signal observed by the South Pole detector. Specifically, it analyses the possible violation of the Lorentz symmetry - according to which the laws of physics must be the same for two observers moving at constant speed relative to each other - predicted by this type of theories.

At the moment, there is no evidence for the existence of this effect, partly because its magnitude would be very small compared to the sensitivity of current experiments. In this sense, astrophysical neutrinos are a very powerful tool for such searches, since, on the one hand, the violation of Lorentz invariance would affect the well-known phenomenon of neutrino flavour oscillations - whereby a certain type of neutrino, with one flavour, turns into another type during its propagation - modifying the signal expected in neutrino telescopes such as IceCube. On the other hand, their high energies and the long distances travelled from their production to their detection on Earth would amplify the magnitude of these new physics effects, bringing them closer to current experimental sensitivity.

This is a high-quality study, backed by the strength of the international IceCube collaboration, a pioneer in the study of high-energy astrophysical neutrinos. It is fully consistent with previous results, which had not detected evidence of Lorentz invariance violation in any of the astroparticle signals studied - photons, cosmic rays, neutrinos, gravitational waves. In the case of neutrinos, the current analysis improves by several orders of magnitude on the limits obtained by the IceCube collaboration itself from observations of atmospheric neutrinos in its 2018 work (ref. 15 of the paper). This is due to the higher energies of astrophysical neutrinos compared to atmospheric neutrinos, which make the expected effect much larger in the former case.

As the authors themselves explain, the work has some limitations. The main limitation is that the Lorentz invariance violation effects can be of different types and, in general, they can appear simultaneously. However, in this paper we assume the presence of only one of these effects at a time. This is a common procedure in this type of studies and its impact is not very important in the result since, for the moment, the focus is on the discovery of this signal. Future precision measurements - should the effect be confirmed - would require more detailed analysis. In any case, these limitations have to be taken into account when analysing the feasibility of quantum gravity models.