cosmology

If there are new neutrino interactions with matter, and if they affect neutrinos of different flavor differently, then they could impact neutrino oscillations. Long-baseline neutrino experiments are well-suited to look for them, thanks to their use of intense, well-characterized neutrino beams.

If the new interactions have a long range—i.e., if they are mediated by a new, ultra-light mediator—then neutrinos on Earth may experience a matter potential sourced by the vast amount of faraway matter elsewhere inside the Earth, Moon, Sun, Milky Way, and in the cosmological matter distribution, as pointed out in 1808.02042 [Universe’s Worth of Electrons to Probe Long-Range Interactions of High-Energy Astrophysical Neutrinos, by MB & Sanjib Agarwalla, PRL 2019]. This boosts the chances of discovering the new interaction even if it is supremely feeble.

In a recent paper (2305.05184 [Flavor-dependent long-range neutrino interactions in DUNE & T2HK: alone they constrain, together they discover, by Masoom Singh, MB, and Sanjib Agarwalla, JHEP 2023]), we explored the prospects of constraining or discovering these new, long-range neutrino interactions in the upcoming long-baseline experiments DUNE and T2HK. We found promising prospects. However, we explored only three different possible forms of the interaction, introduced by gauging three of the accidental global lepton-number U(1) symmetries of the Standard Model.

In a new paper (2404.02775), led by PhD students Masoom Singh and Pragyanprasu Swain, we now extend this to many other symmetries—a plethora of them!—that introduce new neutrino interactions with electrons, neutrons, and protons. Each symmetry affects oscillations differently.

Our new results cement and extend our original findings: DUNE and T2HK should be able to probe the existence of new interactions—and possibly discover and distinguish between alternatives—regardless of which symmetry is responsible for inducing them. The reach of DUNE and T2HK to probe new neutrino interactions is not only deep, but also broad!

Read more at

A plethora of long-range neutrino interactions probed by DUNE and T2HK
Sanjib Kumar Agarwalla, Mauricio Bustamante, Masoom Singh, Pragyanprasu Swain
2404.02775 hep-ph

Download the digitized data from out plots from this GitHub repository.

So far, the flavor composition of high-energy astrophysical neutrinos, i.e., the proportion of electron, muon, and tau neutrinos in their total diffuse flux, has been measured by IceCube only as averaged over the range of observed neutrino energies, between roughly 10 TeV and a few PeV.

This is in spite of the flavor composition likely having a dependence on the neutrino energy, since different neutrino production mechanisms could become accessible at different energies. And, in addition, a myriad of proposed new-physics models could modify the flavor composition in an energy-dependent manner.

Yet, so far, the intrinsic challenge of measuring flavor, combined with the limited number of detected neutrinos, made it unfeasible to measure only the energy-averaged flavor composition, thus washing out our sensitivity to the above energy-dependent effects.

In a new paper led by postdocs Qinrui Liu and Damiano Fiorillo we measure for the first time the energy dependence of the flavor composition using present-day IceCube data—7.5 years of HESE events—and make projections for measurements that use the combined detection of HESE plus through-going muons by multiple planned neutrino telescopes: Baikal-GVD, IceCube-Gen2, KM3NeT, P-ONE, TAMBO, and TRIDENT.

We find no significant evidence for a transition in the flavor composition from low to high energies, but show that in the near future the combined capabilities of the above neutrino telescopes will likely make it possible to detect such a transition, especially if it occurs around 200 TeV.

While the measurement will remain challenging, we expect ongoing and future improvements in event reconstruction and flavor identification to boost our projections beyond what we have shown.

Mauricio Bustamante

Assistant Professor – Niels Bohr Institute, University of Copenhagen

A plethora of long-range neutrino interactions probed by DUNE and T2HK

Measuring the energy dependence of the high-energy astrophysical neutrino flavor composition