How Neutrinos Test the Constancy of the Laws of Physics express
The speed of light in a vacuum is physics' metronome: it sets the rhythm for all processes. If it falters, the familiar harmony collapses. Neutrinos, ubiquitous but almost intangible particles from space, can check if this rhythm ever stumbles under extreme conditions. Future detectors like GRAND and POEMMA will catch neutrinos at the highest energies, where any deviation would appear brightest. If the constancy of the speed of light is violated, neutrino types will transform into each other differently: there will be an anomalously high number of tau neutrinos.
Calculations promise that the new facilities will catch a rhythm glitch tens of times fainter than any previous experiment. Astonishingly, even a microscopic violation of the law of Lorentz and Einstein would cause not just a slight off-key note but a true cacophony — detectors would be flooded by a shower of particles of a single kind. And then the music of the universe would sound entirely new. Or the rhythm will prove flawless, and we will once again confirm its harmony.
Original abstract
as written by the authors arXiv:2604.19880
Neutrino telescopes have detected astrophysical neutrinos with energies up to $${O}(100)$$ PeV. Several current and proposed experiments aim to observe neutrinos at even higher energies, with the goal of detecting cosmogenic neutrinos. This increase in neutrino energy makes tests of Lorentz invariance violation (LIV) particularly appealing, since the effects of higher-dimension LIV operators on neutrino propagation grow rapidly with energy. In this work, we investigate the potential of the upcoming experiments GRAND and POEMMA to probe LIV in the neutrino sector through the detection of ultra-high-energy tau neutrinos. We generate the cosmogenic neutrino flux using SimProp and interface it with a calculation of neutrino flavor transition probabilities in the presence of LIV effects. Deviations from standard flavor transition probabilities manifest as changes in the expected tau neutrino event rates at GRAND and POEMMA. We first consider the case with a single nonzero LIV operator of various dimensions, and find that the projected sensitivities exceed existing limits from lower-energy probes by orders of magnitude. We then explore scenarios with multiple nonzero LIV parameters and show that their interplay can significantly modify the sensitivities compared to the single-parameter case. Overall, we find that upcoming observations of ultra-high-energy tau neutrinos will place some of the most stringent constraints on LIV.
Neutrinos are so elusive that trillions of them pass through your fingernail every second, hardly noticing you.