A Minimal Interpretation of the Galactic Cosmic-Ray Spectrum from GeV to PeV Energies

High-precision measurements of the cosmic-ray (CR) proton spectrum have revealed significant deviations from a simple power-law behaviour. These deviations are characterised by three prominent features: (i) a progressive spectral hardening above approximately 200 GeV, (ii) an excess between 10 and 30 TeV (the multi-TeV bump''), followed by a sharp turnover around 100 TeV, and (iii) a pronounced structure between 0.1 and 10 PeV (the PeV bump’’). We propose a minimal two cosmic-ray population framework that consistently accounts for the observed CR proton spectrum across six decades in energy, from GeV to PeV. In this scenario, the spectral complexity arises naturally from a transition between two Galactic CR proton populations in the 10-100 TeV energy range. The low-energy population exhibits a sharp cutoff at tens of TeV, while a second, higher-energy population emerges and dominates above 100 TeV, terminating with a smooth exponential cutoff at approximately 6.5 PeV. This framework reproduces all observed spectral features without invoking contributions from nearby sources or requiring non-standard assumptions about particle acceleration or propagation. Recent gamma-ray observations of supernova remnants, star-forming regions, and microquasars provide plausible astrophysical candidates for the origin of the two CR components.

💡 Research Summary

The paper presents a phenomenological two‑population model that accounts for the detailed structure observed in the Galactic cosmic‑ray (CR) proton spectrum from a few GeV up to several PeV. Recent high‑precision measurements by AMS‑02, DAMPE, LHAASO and IceTop have revealed three prominent deviations from a simple power‑law: (i) a gradual hardening beginning at ~200 GeV, (ii) an excess (“multi‑TeV bump”) between 10 and 30 TeV followed by a sharp turnover around 100 TeV, and (iii) a broad “PeV bump” spanning 0.1–10 PeV. Traditional single‑population models based on diffusive shock acceleration in supernova remnants (SNRs) cannot simultaneously reproduce all these features without invoking exotic physics, nearby sources, or ad‑hoc propagation effects.

The authors therefore propose a minimal framework consisting of two distinct Galactic proton components. Each component is described by a power‑law with an exponential (or super‑exponential) cutoff:

J_i(E) = A_i E^{‑Γ_i} exp