Constraints on axionlike particles with H.E.S.S. from the irregularity of the PKS2155−304energy spectrum

Abstract

Axionlike particles (ALPs) are hypothetical light (sub-eV) bosons predicted in some extensions of the Standard Model of particle physics. In astrophysical environments comprising high-energy gamma rays and turbulent magnetic fields, the existence of ALPs can modify the energy spectrum of the gamma rays for a sufficiently large coupling between ALPs and photons. This modification would take the form of an irregular behavior of the energy spectrum in a limited energy range. Data from the H.E.S.S. observations of the distant BL Lac object PKS 2155−304 (z = 0.116) are used to derive upper limits at the 95% C.L. on the strength of the ALP coupling to photons, gγa < 2.1 × 10 −11 GeV −1 for an ALP mass between 15 neV and 60 neV. The results depend on assumptions on the magnetic field around the source, which are chosen conservatively. The derived constraints apply to both light pseudoscalar and scalar bosons that couple to the electromagnetic field.

On the impact of magnetic-field models in galaxy clusters on constraints on axion-like particles from the lack of irregularities in high-energy spectra of astrophysical sources

“…Indeed, for instance, in Ref. [27] it was noted that the source belongs to a small unnamed group of galaxies studied in Ref. [64].…”

“…Several attempts to follow this way have been made in recent years, exploiting the observed smoothness of X-and gammaray spectra of strong emitters presumably embedded in astrophysical magnetic fields. In particular, these included analyses of gamma-ray observations of PKS 2155−304 [27,28,29], NGC 1275 [30,31] and several Galactic sources [32,33,34] relevant for ALP masses ∼ 10 −9 − 10 −7 eV (overlapping with the range invoked for explanations of the "anomalous transparency" effects). For lower ALP masses, X-ray observations of 3C 218 [35], the same NGC 1275 [36,37,38], M 87 [39] and some other extragalactic sources [40] were used.…”

Status of the Cherenkov Telescope Array project

“…et al 2009). The emission from distant BL Lacs (limiting distance today is shortly below z ∼ 1) has also been extensively used to study the extragalactic background light (EBL; Abramowski et al 2013b) to search for axions (Abramowski et al 2013a) and violation of the Lorentz invariance principle (Barres de Almeida & Daniel 2012), as well as a means to achieve the difficult task of measuring the intensity of the intergalactic magnetic field IGMF (Arlen et al 2012) Finally, more recently, with the accumulation of data and the improved sensitivity of the current instruments after a series of upgrades (Aleksic et al 2015;Bomont et al 2014), it has been possible to indirectly probe, with relatively good sensitivity, for dark matter annihilation signatures using VHE gamma-ray observations. Results do not hint at any distinguishable signal from DM, but stringent constraints start to be derived for particles with masses up to a few TeV (Abramowski et al 2015).…”

Searching for the possible signal of the photon-axionlike particle oscillation in the combined GeV and TeV spectra of supernova remnants

“…Besides, the conversion between γ-ray photons and ALPs in external magnetic fields could create energy-dependent modulations in spectra of γ-ray sources, which is so called the photon-ALP oscillation. Such a spectral oscillation effect could be a smoking-gun signature for the existence of ALPs [16][17][18][19][20][21] and has been widely used to search for ALP signals [22][23][24][25][26][27][28][29][30][31][32][33]. The Fermi-LAT Collaboration have searched for the photon-ALP oscillation signal in the High Energy (HE) spectrum of NGC 1275 and excluded the coupling g aγ above 5×10 −11 GeV −1 for ALP masses 0.5−5 neV [26].…”

“…The HE and Very High Energy (VHE) photons from PKS 2155-304 have also been analyzed separately by the H.E.S.S. Collaboration [23] and Zhang et al [28] without significant signal of ALPs found. The γ-ray spectra of bright pulsars [29][30][31] and SNRs [32] obtained from the Fermi-LAT data show intriguing indications for the photon-ALP oscillation, but the best-fit parameters are in tension with the limit from the CAST helioscope.…”