The detection of very high-energy neutrinos by IceCube experiment supports the existence of a comparable gamma-ray counterpart from the same cosmic accelerators. Under the likely assumption that the ...sources of these particles are of extragalactic origin, the emitted photon flux would be significantly absorbed during its propagation over cosmic distances. However, in the presence of photon mixing with ultra-light axion-like-particles (ALPs), this expectation would be strongly modified. Notably, photon-ALP conversions in the host galaxy would produce an ALP flux which propagates unimpeded in the extragalactic space. Then, the back-conversion of ALPs in the Galactic magnetic field leads to a diffuse high-energy photon flux. In this context, the recent detection of the diffuse high-energy photon flux by the Large High Altitude Air Shower Observatory (LHAASO) allows us to exclude at the
95
%
CL an ALP-photon coupling
g
a
γ
≳
3.9
–
7.8
×
10
-
11
GeV
-
1
for
m
a
≲
4
×
10
-
7
eV
, depending on the assumptions on the magnetic fields and on the original gamma-ray spectrum. This new bound is complementary with other ALP constraints from very-high-energy gamma-ray experiments and sensitivities of future experiments.
The Milky Way magnetic field can trigger conversions between photons and axionlike particles (ALPs), leading to peculiar features on the observable photon spectra. Previous studies considered only ...the regular component of the magnetic field. However, observations consistently show the existence of an additional turbulent component, with a similar strength and correlated on a scale of a few 10 pc. We investigate the impact of the turbulent magnetic field on the ALP-photon conversions, characterizing the effects numerically and analytically. We show that the turbulent magnetic field can change the conversion probability by up to a factor of two and may lead to observable irregularities in the observable photon spectra from different astrophysical sources.
Large-scale extragalactic magnetic fields may induce conversions between very-high-energy photons and axionlike particles (ALPs), thereby shielding the photons from absorption on the extragalactic ...background light. However, in simplified "cell" models, used so far to represent extragalactic magnetic fields, this mechanism would be strongly suppressed by current astrophysical bounds. Here we consider a recent model of extragalactic magnetic fields obtained from large-scale cosmological simulations. Such simulated magnetic fields would have large enhancement in the filaments of matter. As a result, photon-ALP conversions would produce a significant spectral hardening for cosmic TeV photons. This effect would be probed with the upcoming Cherenkov Telescope Array detector. This possible detection would give a unique chance to perform a tomography of the magnetized cosmic web with ALPs.
We have analyzed the physics potential of a reference next-generation detector in providing information on (galactic and extragalactic) supernova neutrino flavor transitions.
A fraction of active galactic nuclei producing very high-energy (VHE) gamma rays are located in galaxy clusters. The magnetic field present in the intracluster medium would lead to conversions of VHE ...photons into axionlike particles (ALPs), which are a generic prediction of several extensions of the Standard Model. ALPs produced in this way would traverse cosmological distances unaffected by the extragalactic background light at variance with VHE photons which undergo a substantial absorption. Eventually, a nontrivial fraction of ALPs would reconvert into VHE photons in the magnetic field of the Milky Way. An independent laboratory check of ultralight ALPs invoked in this mechanism can be performed with the planned upgrade of the photon regeneration experiment Any Light Particle Search at Deutsches Elektronen-Synchrotron and with the next generation solar axion detector International Axion Observatory.
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