Simulating the Diffuse Neutrino Emission from the Milky Way with GALPROP

TL;DR

The paper advances the modeling of the Milky Way's diffuse neutrino emission by integrating updated GALPROP CR propagation with AAfrag cross sections and exploring multiple spiral-arm and uniform CR source configurations, all calibrated to local CR measurements. Neutrino fluxes are computed via line-of-sight integration of hadronic emissivities and are compared against IceCube Galactic-plane results and LHAASO gamma-ray constraints, incorporating unresolved-source and pair-absorption effects. The main finding is that the GALPROP predictions are consistent with IceCube within uncertainties and with LHAASO-derived expectations, but underpredict the total IceCube Galactic-plane flux by factors of a few, suggesting a non-negligible hadronic component (and GC-related underestimation) alongside a leptonic contribution needed to explain LHAASO data. These results provide state-of-the-art, open-model predictions for VHE neutrino emission from the Galaxy and offer valuable templates for future neutrino searches while highlighting uncertainties in gamma–neutrino conversions and unresolved-source fractions.

Abstract

We use the GALPROP cosmic ray (CR) propagation framework to model the diffuse neutrino and gamma-ray emissions from the Galaxy. A collection of realistic bounding models are developed and predictions of the resulting neutrino and gamma-ray signals are compared to the IceCube and LHAASO data up to PeV energies. We find that all the GALPROP models are consistent with the neutrino data within uncertainties. They are also consistent with expectations of neutrino emissions derived from LHAASO data when accounting for possible gamma-ray point source contamination. The new models present state-of-the-art predictions for the VHE neutrino emissions from the Galaxy that may be used for future neutrino searches.

Figures (6)

• Figure 1: Skymap of the GALPROP predicted Galactic diffuse per-flavour neutrino flux at 100 TeV. The top panel shows the GALPROP predictions for the SA50 source distribution, and the bottom panel is smeared with a $\sigma = 7^{\circ}$ Gaussian corresponding to the IceCube event uncertainty at 100 TeV.
• Figure 2: Envelopes of the GALPROP predicted all-sky diffuse per-flavour neutrino flux across the three source distributions (SA variation; green band) and over variations in the injection spectral index ($\gamma_{2}$ variation, green hatched band). Also shown are the three model-dependent IceCube Galactic plane flux measurements 2023Sci...380.1338I: $\pi^{0}$ (black), KRA$_{\gamma}^{5}$ (orange), and KRA$_{\gamma}^{50}$ (blue).
• Figure 3: The GALPROP predicted diffuse per-flavour neutrino flux towards to inner (top) and outer (bottom) LHAASO regions across the three source distributions (SA variation; green band) and over variations in the injection spectral index ($\gamma_{2}$ variation, green hatched band). The LHAASO diffuse $\gamma$-ray results are shown after converting to expected neutrino fluxes assuming that the emission is 100% hadronic (upper limit, grey) and 25% hadronic (lower limit, black), with the statistical and systematic uncertainties added in quadrature. The vertical dotted line at $E_{\nu}=20$ TeV (equivalent to $E_{\gamma}=40$ TeV) denotes the region where pair absorption effects reduce the accuracy of the LHAASO $\gamma$-to-$\nu$ conversion.
• Figure 4: Longitudinal profile taken for $|b| \leq 5^{\circ}$ of the GALPROP predicted per-flavour neutrino flux at $E_{\nu}=100$ TeV across u50 (dotted red), SA0 (solid orange), SA50 (dash-dotted green), and SA100 (dashed cyan) source distributions. The analysis was performed on the skymap with a $\sigma = 7^{\circ}$ Gaussian smear from \ref{['fig:neutrino skymaps']}. Also shown is a lower-bound estimate of the LHAASO data points (black) from 2024ChPhC..48k5105C after converting to a neutrino flux (\ref{['eq:pi-to-nu conversion']}) and subtracting an estimated source component of 75%.
• Figure 5: Proton kinetic energy spectrum above 50 GeV at the Solar location. The GALPROP propagated spectrum is shown for three values of the highest-energy injection index. Observational datapoints are from AMS--02 2021PhR...894....1A, DAMPE 2019SciA....5.3793A, CALET 2022PhRvL.129j1102A, ISS--CREAM 2022ApJ...940..107C, NUCLEON 2019AdSpR..64.2546G, and LHAASO 2025arXiv250514447T.