Are Galactic-plane neutrinos diffuse or from discrete sources?
In plain words
In 2023 IceCube detected neutrinos from the plane of the Milky Way; they could come from cosmic rays hitting interstellar gas everywhere or from a set of individual sources.
Precise statement
IceCube found Galactic-plane neutrino emission at $4.5\,\sigma$ (2023), consistent with diffuse templates built from cosmic-ray interactions with gas. Determine the fraction from unresolved sources (PeVatrons such as the LHAASO sources above $1\mathrm{e}14\,\mathrm{eV}$) versus diffuse interactions, and whether the flux requires harder cosmic-ray spectra in the inner Galaxy than near the Sun. Answer: the source fraction and the neutrino spectrum, consistent with diffuse gamma-ray maps above $1\mathrm{e}14\,\mathrm{eV}$.
What would settle it
Joint fits of neutrino maps from IceCube and Northern-Hemisphere detectors (KM3NeT, Baikal-GVD), which view the inner Galaxy better, with LHAASO diffuse gamma-ray maps.
Status in the literature
2023: IceCube reported $4.5\sigma$ Galactic-plane emission, of order 10 percent of the all-sky astrophysical flux near $30\ \mathrm{TeV}$.