Today, the values of the neutrino mixing angles and mass differences that govern flavor transitions are known to quite high precision. However, we know them exclusively from sub-TeV terrestrial experiments. Because these experiments operate at low transferred momenta (typically, Q ~ few GeV), a fundamental question remains: are the mixing parameters universal constants, or do they evolve at high energies?

Quantum field theory dictates that these parameters should “run” with Q via renormalization group (RG) equations. While this running is negligible in the Standard Model, well-motivated new-physics frameworks, like the Standard Model Effective Field Theory (SMEFT), can accelerate this evolution. Detecting the high-energy running of neutrino mixing parameters would be a smoking-gun signature of new physics.

To access the high-Q regime, we turn to high-energy astrophysical neutrinos, with energies in the TeV–PeV and EeV ranges. They interact in neutrino telescopes via deep inelastic scattering and probe average momentum transfers of Q ~ 20-40 GeV, offering an unprecedented window into this high-Q evolution.

In a new paper with Qinrui Liu and Gabriela Barenboim, we evaluate the power of high-energy astrophysical neutrinos to test the evolution of neutrino mixing. We use the neutrino flavor composition at Earth, i.e., the relative proportions of electron, muon, and tau neutrinos in the diffuse flux. We execute a two-pronged analysis: first, extracting generic high-Q mixing parameters to remain model-agnostic, and second, constraining RG-inducing dimension-6 SMEFT coefficients.

We extract present bounds from the 11.4-year IceCube Medium Energy Starting Events (MESE) sample, published in 2025. Because the uncertainties in current flavor measurements are large, present data cannot yet meaningfully constrain the high-Q mixing parameters or SMEFT operators.

However, the future is promising. For our projections, we simulate the combined detection capabilities of existing (IceCube, Baikal-GVD, KM3NeT) and upcoming (P-ONE, IceCube-Gen2, NEON, TRIDENT, HUNT) optical-Cherenkov neutrino telescopes by the years 2040 and 2050, using both High-Energy Starting Events (HESE) and through-going muons. Crucially, we profile over the unknown astrophysical source flavor composition to ensure our bounds are robust and realistic.

Our results show that by 2040–2050, this global network will achieve the precision necessary to place unprecedented bounds on high-Q mixing (yielding particularly strong constraints in the 23 and 13 sectors). Furthermore, if the astrophysical neutrinos are produced via muon-damped pion decay, these telescopes will be capable of placing limits on individual SMEFT coefficients at a new-physics scale of 1 TeV, easily translatable to other energy scales.

We also forecasted the sensitivity of ultra-high-energy (UHE) radio arrays, such as the planned IceCube-Gen2 radio array. Counterintuitively, we found that despite UHE neutrinos possessing much higher energies, they yield drastically weaker constraints than their TeV–PeV counterparts. This is driven both by the logarithmic scaling of the RG evolution and by the vast experimental uncertainties inherent to radio-based flavor tagging.

Read more at:

Astrophysical bounds on the high-energy evolution of neutrino mixing
Mauricio Bustamante, Qinrui Liu, Gabriela Barenboim
2604.14409 hep-ph