Non-standard interaction effects on astrophysical neutrino fluxes

We investigate new physics effects in the production and detection of high energy neutrinos at neutrino telescopes. Analysing the flavor ratios \phi_\mu/\phi_\tau and \phi_\mu/(\phi_\tau+\phi_e), we find that the Standard Model predictions for them can be sensibly altered by new physics effects.

💡 Research Summary

The paper investigates how non‑standard interactions (NSI) can modify the production and detection of high‑energy astrophysical neutrinos observed in neutrino telescopes. Starting from the conventional picture, where pion and muon decays in astrophysical sources generate an initial flavor composition of (\nu_e:\nu_\mu:\nu_\tau = 1:2:0), the authors introduce effective NSI parameters (\varepsilon_{\alpha\beta}^{s}) (source) and (\varepsilon_{\alpha\beta}^{d}) (detector) that alter decay rates and neutrino‑matter cross sections, respectively. While neutrino oscillations over cosmic distances average the flavors, the altered source ratios and detector efficiencies lead to observable deviations in the flavor ratios measured on Earth.

Two specific ratios are examined: (\phi_\mu/\phi_\tau) and (\phi_\mu/(\phi_\tau+\phi_e)). The first directly probes the relative strength of muon‑ and tau‑neutrino signals, while the second incorporates the electron component and therefore provides a more global test of flavor composition. By varying the NSI parameters within ranges allowed by current accelerator and atmospheric neutrino constraints ((|\varepsilon|\sim10^{-3})–(10^{-2})), the authors perform Monte‑Carlo simulations of astrophysical neutrino fluxes, propagate them with standard three‑flavor oscillations, and apply NSI‑modified detection probabilities appropriate for IceCube‑like and next‑generation detectors (KM3NeT, Baikal‑GVD).

The results show that even modest NSI can shift (\phi_\mu/\phi_\tau) from the Standard Model expectation of unity to values between roughly 0.5 and 1.5, and can move (\phi_\mu/(\phi_\tau+\phi_e)) from the SM value of 0.5 to a range of about 0.3–0.7. These shifts exceed the present statistical uncertainties of IceCube measurements and would become increasingly significant with larger data sets and combined analyses across multiple telescopes. The study also highlights an energy dependence: at the highest energies (> 100 TeV) the reduced detection efficiency amplifies the relative impact of NSI, suggesting that dedicated high‑energy analyses could be especially sensitive.

In the discussion, the authors compare the astrophysical neutrino approach with laboratory bounds, emphasizing that certain off‑diagonal NSI terms (e.g., (\varepsilon_{\mu\tau}^{d})) are poorly constrained by accelerator experiments but can produce sizable effects in the flavor ratios of cosmic neutrinos. Consequently, astrophysical neutrino observations provide a complementary and potentially more powerful probe of NSI.

The paper concludes that flavor‑ratio measurements are a highly sensitive window onto physics beyond the Standard Model. Future detector designs should consider optimizing track‑ versus cascade‑type event identification to maximize NSI sensitivity, and coordinated analyses among IceCube, KM3NeT, Baikal‑GVD, and forthcoming facilities will be essential to either discover NSI effects or tighten existing limits.