arXiv subjects

Alessandro Cermenati

Publications and source records attributed to Alessandro Cermenati.

3 recordsLinked to original sources

arXiv2026

Self-confinement of ultra-high-energy nuclei in cosmic filaments: implications for the UHECR spectrum and composition

The spectrum and composition of ultra-high-energy cosmic rays (UHECRs) suggest that the population dominating above the ankle releases particles with an unusual hard spectrum at low rigidity, below the EV scale. In self-confinement scenarios, such an apparent hardening arises from transport: escaping UHECRs generate magnetic turbulence that delays their own release from the magnetized environments surrounding their sources. We extend the self-confinement scenario based on the non-resonant streaming instability to a mixed nuclear composition. We describe the confinement region with an effective leaky-box model including escape, photodisintegration, and secondary production. We then compare the resulting spectrum and composition with Auger measurements and compute the associated cosmogenic neutrino and gamma-ray emission. We find that self-generated turbulence can suppress the escaping flux below the EV scale for source luminosities and magnetic-field coherence lengths compatible with UHECR sources hosted in galaxy clusters and propagating through cosmic filaments. During confinement, heavy nuclei efficiently photodisintegrate, producing secondary protons that contribute below the ankle and help account for the observed composition. The predicted neutrino flux remains compatible with current limits, while the diffuse gamma-ray background provides a potentially strong constraint on the most extreme configurations.

astro-ph.HE↗

arXiv2025

Scrutinizing the cosmogenic origin of the KM3-230213A event: A Multimessenger Perspective

The recent detection of the neutrino event KM3-230213A ($\sim$~220 PeV) by the KM3NeT/ARCA telescope, the most energetic ever observed, could represent the long-awaited evidence for a cosmogenic origin, arising from the interaction of an ultra-high-energy cosmic ray with background photons. Its secure confirmation would mark a major advance in high-energy astrophysics. We perform a self-consistent multimessenger transport calculation of protons and their secondary $\gamma$-rays and neutrinos from cosmologically evolving sources, confronting predictions with data from the Pierre Auger Observatory, IceCube, KM3NeT, and the Fermi-LAT isotropic $\gamma$-ray background. A steep sub-ankle proton component saturates the diffuse $\gamma$-ray background and is disfavoured, whereas a hard proton spectrum extending beyond $10^{20}$~eV with evolution $\propto (1+z)^3$ reproduces KM3-230213A without violating any limits. This scenario requires a proton fraction $\lesssim 10$\% at $3\times 10^{19}$~eV and excludes faster-evolving sources. Joint UHE-neutrino and $\gamma$-ray observations thus sharpen constraints on extragalactic cosmic-ray sources and set targets for AugerPrime and next-generation neutrino telescopes.

astro-ph.HE↗

arXiv2025

Excitation of the non-resonant streaming instability around sources of Ultra-High Energy Cosmic Rays

The interpretation of the ultra-high-energy cosmic ray spectrum (UHECRs) and composition suggests a suppression of the flux below $\sim$1 EeV, as observed by the Pierre Auger Observatory and Telescope Array. A natural explanation for this phenomenon involves magnetic confinement effects. We investigate the possibility that UHECRs self-generate the magnetic turbulence necessary for such confinement via current-driven plasma instabilities. Specifically, we show that the electric current produced by escaping UHECRs can excite a non-resonant streaming instability in the surrounding plasma. This instability reduces the diffusion coefficient in the source environment, effectively trapping particles with energies $E \lesssim 0.6$ EeV $\mathcal{L}_{45}^{1/2} R_{\text{Mpc}}^{-1} \lambda_{10}^{2}$ for times exceeding the age of the Universe. Here, $\mathcal{L}_{45}$ is the source luminosity in units of $10^{45}$ erg/s, $R_{\text{Mpc}}$ is the radial size in Mpc, and $\lambda_{10}$ is the intergalactic magnetic field coherence length in units of 10 Mpc. We discuss in detail the conditions, in terms of source luminosity, initial magnetic field, and the environment in which this phenomenon occurs, that need to be fulfilled in order for self-confinement to take place near a source of UHECRs. By modeling a population of UHECR sources with a luminosity function typical of extragalactic gamma-ray sources, we connect the spectrum of escaping particles to the luminosity distribution. Furthermore, we calculate the contribution of these confined particles to cosmogenic neutrino production, finding consistency with current observational constraints. Our results suggest that self-induced turbulence may play an important role in shaping the UHECR spectrum and, in particular, may account for the flux suppression near their sources, offering a promising framework for interpreting current observations.

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