arXiv subjects

Francesco Schiavone

Publications and source records attributed to Francesco Schiavone.

5 recordsLinked to original sources

arXiv2026

Projected sensitivity of CTAO to axion-like particles from blazars with a machine learning approach

Blazars are a class of active galactic nuclei, supermassive black holes located at the centres of distant galaxies characterised by strong emission across the entire electromagnetic spectrum, from radio waves to gamma rays. Their relativistic jets, closely aligned to the line of sight from Earth, are a rich and complex environment, characterised by the presence of strong magnetic fields over parsec-scale lengths. Owing to their cosmological distance from Earth, these sources serve as ideal targets to probe non-standard gamma-ray propagation. In particular, axion-like particles (ALPs) could be detected through their coupling to photons, which enables ALP-photon conversions in external magnetic fields, leading to distinct signatures in the blazars' gamma-ray spectra. In this work, we estimate the potential of the Cherenkov Telescope Array Observatory (CTAO) to constrain the ALP parameter space by simulating observations of two bright blazars, Mrk 501 and PKS 2155$-$304. We obtain projected $2σ$ exclusion regions, demonstrating that CTAO will be able to consistently improve present limits thanks to its greater energy resolution and point-source sensitivity with respect to present ground-based gamma-ray telescopes. In addition to the standard statistical technique based on the likelihood ratio test, we further demonstrate the application of a new method based on machine learning classifiers, which may help in reducing the effect of systematic model-dependent uncertainties in future ALP searches.

astro-ph.HE↗

arXiv2025

Recent observations of PKS 2155-304 with MAGIC and LST-1 in a multi-wavelength context

PKS 2155-304 is a well-known high-frequency peaked BL Lac (HBL) at redshift z=0.116, which has been extensively studied across the electromagnetic spectrum due to its rapid and large-amplitude variability. Several violent outbursts in X-rays and $γ$-rays have been observed in the past, with intra-night variability in very-high-energy $γ$-rays (VHE; E > 100 GeV) detected down to the minute timescale. The alternation of quiescent and enhanced states, observed with a tentative quasi-periodicity of 1.74 $\pm$ 0.13 years in high-energy (HE; 100 MeV < E < 100 GeV) $γ$-rays, makes this source a key target also for ground-based $γ$-ray instruments and in particular for the Imaging Atmospheric Cherenkov Telescopes. Its brightness, proximity, and well-determined redshift make this $γ$-ray source a prime target for fundamental physics studies, including tests of Lorentz Invariance Violation (LIV), searches for axion-like particles (ALPs), and constraints on the distribution of the extragalactic background light (EBL). In the last two years, PKS 2155-304 has been independently monitored by the Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) telescopes and the first Large-Sized Telescope (LST-1) of the Cherenkov Telescope Array Observatory (CTAO) located at the Roque de Los Muchachos Observatory (La Palma, Spain). The observations were carried out at large zenith angles (LZA; ZA > 55°), and the VHE data have been complemented with simultaneous observations in HE $γ$-rays (Fermi-LAT), X-rays (Swift-XRT) and optical wavelengths (ASAS-SN).

astro-ph.HE↗

arXiv2025

Dark matter and fundamental physics with the Cherenkov Telescope Array Observatory

The Cherenkov Telescope Array Observatory (CTAO) will be the next-generation major ground-based gamma-ray observatory. It will be made up of two large arrays of imaging atmospheric Cherenkov telescopes (IACTs), with one site in the Northern hemisphere (La Palma, Canary Islands) and one in the Southern (Paranal, Chile). CTAO aims to offer great improvement in energetic and angular resolution with respect to current IACT systems, spanning a photon energy range from 20 GeV to 300 TeV, as well as a significantly larger effective area and full-sky coverage. Besides a percentage of observational time available for external proposals, making it the first open gamma-ray observatory, the core observational program of CTAO is organized in several Key Science Projects. A significant amount of time will be devoted to dark matter (e.g. WIMPs, axion-like particles) and fundamental physics studies from a variety of targets, including the Milky Way's Galactic centre, dwarf spheroidal galaxies, the Large Magellanic Cloud, and extragalactic objects such as blazars. In this contribution, an overview of CTAO's main features is provided, with a focus on its capabilities to investigate these yet unanswered questions of modern physics.

astro-ph.HE↗

arXiv2025

A machine learning approach to axion-like particle searches in CTAO observations of blazars

Axion-like particles (ALPs) are a common prediction of several extensions of the Standard Model of particle physics and could be detected through their coupling to photons, which enables ALP-photon conversions in external magnetic fields. This conversion could lead to two distinct signatures in gamma-ray spectra of blazars: a superimposition of energy-dependent "wiggles" on the spectral shape, and a hardening at high (multi-TeV) energies, due to the ALP beam eluding absorption by the extragalactic background light (EBL). The enhanced energy resolution of the Cherenkov Telescope Array Observatory (CTAO) with respect to present ground-based gamma-ray telescopes makes it an ideal instrument to probe such phenomena. In this contribution, we explore a different approach based on the use of machine learning (ML) classifiers and compare it to the standard method. Our preliminary results suggest that both techniques yield consistent results, with the ML-based method offering comparable or even slightly broader coverage, potentially extending the CTAO sensitivity beyond existing constraints.

astro-ph.HE↗

arXiv2021

Axion-like particles from primordial black holes shining through the Universe

We consider a cosmological scenario in which the very early Universe experienced a transient epoch of matter domination due to the formation of a large population of primordial black holes (PBHs) with masses $M \lesssim 10^{9}\,\textrm{g}$, that evaporate before Big Bang nucleosynthesis. In this context, Hawking radiation would be a non-thermal mechanism to produce a cosmic background of axion-like particles (ALPs). We assume the minimal scenario in which these ALPs couple only with photons. In the case of ultralight ALPs ($m_a \lesssim 10^{-9}\,\textrm{eV}$) the cosmic magnetic fields might trigger ALP-photon conversions, while for masses $m_a \gtrsim 10\,\textrm{eV}$ spontaneous ALP decay in photon pairs would be effective. We investigate the impact of these mechanisms on the cosmic X-ray background, on the excess in X-ray luminosity in Galaxy Clusters, and on the process of cosmic reionization.

hep-ph↗