First constraints on axion-like particles from Galactic sub-PeV gamma rays

Abstract

Experimental refinements and technical innovations in the field of extensive air shower telescopes have enabled measurements of Galactic cosmic-ray interactions in the sub-PeV (100 TeV to 1 PeV) range, providing new avenues for the search for new physics and dark matter. For the first time, we exploit sub-PeV (10 TeV -1 PeV) observations of Galactic diffuse gamma rays by Tibet ASγ and HAWC to search for an axion-like-particle (ALP) induced gamma-ray signal directly linked to the origin of the IceCube extragalactic high-energy neutrino flux. Indeed, the production of high-energy neutrinos in extragalatic sources implies the concomitant production of gamma rays at comparable energies. Within the magnetic field of the neutrino emitting sources, gamma rays may efficiently convert into ALPs and escape their host galaxy unattenuated, propagate through intergalactic space, and reconvert into gamma rays in the magnetic field of the Milky Way. Such a scenario creates an all-sky diffuse high-energy gamma-ray signal in the sub-PeV range. Accounting for the guaranteed Galactic astrophysical gamma-ray contributions from cosmic-ray interactions with gas and radiation and from sub-threshold sources, we set competitive upper limits on the photon-ALP coupling constant gaγγ. We find gaγγ < 2.1 × 10 −11 GeV −1 for ALP masses ma ≤ 2 × 10 −7 eV at a 95% confidence level, progressively closing the mass gap towards ADMX limits.

Prospects for detection of a galactic diffuse neutrino flux

“…Moreover, since the spectral energy distributions of the KRA 5 γ and γoptimized Max models are very close below 100 TeV, the hint of an excess tracing the former model found by the IceCube collaboration should hold also for the updated γ-optimized Max model. Remarkably, this is also the model which, for γrays, better matches the Tibet ASγ results (see Figures 4, 5 and Figure 3 of Eckner and Calore (2022)).…”

Constraining axion-like particles with the diffuse gamma-ray flux measured by the Large High Altitude Air Shower Observatory

“…We want to point out that the different choice of E b respect to Ref. [46,47], where E b = 25 TeV, has no impact on the final result of this work because it does not strongly affect the detected flux at the energies of interest, close to 300 TeV. Indeed, the normalization of the neutrino spectrum in Eq.…”

“…Indeed, the normalization of the neutrino spectrum in Eq. ( 2) is fixed from the measurement of the diffuse neutrino flux dφ ν /dE at 100 TeV by inverting the following equation [47]:…”

Constraining axion-like particles with the diffuse gamma-ray flux measured by the Large High Altitude Air Shower Observatory

“…Following this interesting result, we take advantage of the recent preliminary measurement of the diffuse gamma-ray flux by the Large High Altitude Air Shower Observatory (LHAASO) [48,49] to present a new bound on ALPs, complementary to the one of Ref. [47].…”

“…In this regard, the recent Ref. [47] used the diffuse gamma-ray signal measured by Tibet ASγ and HAWC to search for ALPs, constraining g aγ 2.1 × 10 −11 GeV −1 for m a < 10 −7 eV. Following this interesting result, we take advantage of the recent preliminary measurement of the diffuse gamma-ray flux by the Large High Altitude Air Shower Observatory (LHAASO) [48,49] to present a new bound on ALPs, complementary to the one of Ref.…”