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Several extensions of the Standard Model predict the existence of Axion-Like Particles (ALPs), very light spin-zero bosons with a two-photon coupling. ALPs can give rise to observable effects in very-high-energy astrophysics. Above roughly…

High Energy Astrophysical Phenomena · Physics 2015-06-05 Marco Roncadelli , Alessandro De Angelis , Giorgio Galanti

Many extensions of the Standard Model predict the existence of ALPs, which are very light spin-zero bosons with a two-photon coupling. Photon-ALP oscillations occur in the presence of an external magnetic field, and ALPs can lead to…

High Energy Astrophysical Phenomena · Physics 2015-03-19 Alessandro De Angelis , Giorgio Galanti , Marco Roncadelli

Axion-like particles (ALPs), predicted in theories beyond the Standard Model, can have observational effects on the transparency of the Universe to $\gamma$ rays in the presence of magnetic fields. In this work, we search for effects…

High Energy Astrophysical Phenomena · Physics 2020-10-30 Rolf Buehler , Galo Gallardo , Gernot Maier , Alberto Domínguez , Marcos López , Manuel Meyer

The idea that photons can convert into axion-like particles (ALPs) $\gamma \to a$ in or around an AGN and reconvert back into photons $a \to \gamma$ in the Milky Way magnetic field has been put forward in 2008 and has recently attracted…

High Energy Astrophysical Phenomena · Physics 2015-05-20 Fabrizio Tavecchio , Marco Roncadelli , Giorgio Galanti

Axion-like particles (ALPs) are a broad class of pseudo-scalar bosons that generically arise from broken symmetries in extensions of the standard model. In many scenarios, ALPs can mix with photons in regions with high magnetic fields.…

High Energy Physics - Phenomenology · Physics 2022-03-10 Sunniva Jacobsen , Tim Linden , Katherine Freese

Axion-like particles (ALPs) are light, neutral, pseudo-scalar bosons predicted by several extensions of the Standard Model of particle physics -- such as the String Theory -- and are supposed to interact primarily only with two photons. In…

High Energy Astrophysical Phenomena · Physics 2019-11-22 Giorgio Galanti

Axion-like particles (ALPs) are very light, neutral, spin zero bosons predicted by many theories which try to complete the standard model of elementary particles. ALPs interact primarily with two photons and can generate photon-ALP…

High Energy Astrophysical Phenomena · Physics 2023-02-09 Giorgio Galanti

An intriguing possibility to partially circumvent extragalactic background light (EBL) absorption in very-high-energy (VHE) observations of blazars is that photons convert into axion-like particles (ALPs) $\gamma \to a$ inside or close to a…

High Energy Astrophysical Phenomena · Physics 2014-09-11 F. Tavecchio , G. Galanti , M. Roncadelli

Prompted by the increasing interest of axion-like particles (ALPs) for very-high-energy (VHE) astrophysics, we have considered a full scenario for the propagation of a VHE photon/ALP beam emitted by a BL Lac and reaching us in the light of…

High Energy Astrophysical Phenomena · Physics 2019-05-02 Giorgio Galanti , Fabrizio Tavecchio , Marco Roncadelli , Carmelo Evoli

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.…

High Energy Astrophysical Phenomena · Physics 2025-09-30 Francesco Schiavone , Leonardo Di Venere , Francesco Giordano

Axion-like particles (ALPs) are a common prediction of certain theories beyond the Standard Model and couple to photons in the presence of external magnetic fields. As a consequence, photon-ALP conversions could lead to an enhancement of…

High Energy Astrophysical Phenomena · Physics 2014-12-09 Manuel Meyer

In this review, we present a self-contained introduction to axion-like particles (ALPs) with a particular focus on their effects on photon polarization: both theoretical and phenomenological aspects are discussed. We derive the photon…

High Energy Physics - Phenomenology · Physics 2024-08-01 Giorgio Galanti

Discoveries of very high energy (VHE) photons from distant blazars suggest that, after correction by extragalactic background light (EBL) absorption, there is a flatness or even a turn-up in their spectra at the highest energies that cannot…

Cosmology and Nongalactic Astrophysics · Physics 2015-05-28 A. Dominguez , M. A. Sanchez-Conde , F. Prada

The very high energy (VHE, E $>$ $100 \mathrm~{GeV}$) $\gamma$-ray observations offer a possibility of indirectly detecting the presence of axion-like particles (ALPs). The paper focuses on detecting photon-ALP oscillations on $\gamma$-ray…

High Energy Astrophysical Phenomena · Physics 2025-03-03 L. J. Dong , Y. G. Zheng , S. J. Kang , C. Y. Yang

The oscillation of photons and axion-like particles (ALPs) in the astrophysical magnetic fields could modify the measured very high energy (VHE; $\mathcal{E}\gtrsim 100\, \rm GeV$) $\gamma$-ray spectra of the blazar sources. In this paper,…

High Energy Astrophysical Phenomena · Physics 2022-02-23 Hai-Jun Li

The detection of very high-energy (VHE) gamma rays from the active galaxy M87 by LHAASO, showing a possible spectral hardening around $20$ TeV, motivates the search for new physics beyond standard emission models. One promising candidate is…

High Energy Astrophysical Phenomena · Physics 2026-04-01 A. Pratts , D Avila Rojas , J. Serna-Franco , M. M. González , R. Alfaro

Axionlike particles (ALPs) could mix with photons in the presence of astrophysical magnetic fields. Searching for this effect in gamma-ray observations of blazars has provided some of the strongest constraints on ALP parameter space so far.…

High Energy Astrophysical Phenomena · Physics 2022-02-02 James Davies , Manuel Meyer , Garret Cotter

Axion-like particles (ALPs) may undergo mixing with photons in the presence of astrophysical magnetic fields, leading to alterations in the observed high energy $\gamma$-ray spectra. In this study, we investigate the ALP-photon oscillation…

High Energy Astrophysical Phenomena · Physics 2024-03-06 Lin-Qing Gao , Xiao-Jun Bi , Jun-Guang Guo , Wenbin Lin , Peng-Fei Yin

We consider the largest observed sample including all intermediate-frequency peaked (IBL) and high-frequency peaked (HBL) flaring blazars above 100 GeV up to redshift $z = 0.6$. We show that the best-fit regression line of the emitted…

High Energy Astrophysical Phenomena · Physics 2020-04-22 Giorgio Galanti , Marco Roncadelli , Alessandro De Angelis , Giovanni F. Bignami

Axion-like particles (ALPs) are hypothetical particles and compelling candidates for cold dark matter. Their existence could be probed through their conversions into photons in the presence of magnetic fields. In this work, we explore the…

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