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Register a new userSearches for Axionlike Particles Using Gamma-Ray Observations
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Manuel Meyer
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Axionlike particles (ALPs) are a common prediction of theories beyond the Standard Model of particle physics that could explain the entirety of the cold dark matter. These particles could be detected through their mixing with photons in external electromagnetic fields. Here, we provide a short review over ALP searches that utilize astrophysical $gamma$-ray observations. We summarize current bounds as well as future sensitivities and discuss the possibility that ALPs alter the $gamma$-ray opacity of the Universe.
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G. Galanti and M .Roncadelli recently made public some comments on the article by D. Wouters and P. Brun about irregularities induced by photon mixing to axion-like particles in astrophysical media [Phys. Rev. D86, 043005 (2012)]. They claim in particular to have found some mistakes in the article. This note is a response to their comments, we refute their arguments and show that the results presented in the article are correct. It turns out most of the misunderstandings come from the definition of the beam initial state, some clarifications about which are given here.
Reactor neutrino experiments provide a rich environment for the study of axionlike particles (ALPs). Using the intense photon flux produced in the nuclear reactor core, these experiments have the potential to probe ALPs with masses below 10 MeV. We explore the feasibility of these searches by considering ALPs produced through Primakoff and Compton-like processes as well as nuclear transitions. These particles can subsequently interact with the material of a nearby detector via inverse Primakoff and inverse Compton-like scatterings, via axio-electric absorption, or they can decay into photon or electron-positron pairs. We demonstrate that reactor-based neutrino experiments have a high potential to test ALP-photon couplings and masses, currently probed only by cosmological and astrophysical observations, thus providing complementary laboratory-based searches. We furthermore show how reactor facilities will be able to test previously unexplored regions in the $sim$MeV ALP mass range and ALP-electron couplings of the order of $g_{aee} sim 10^{-8}$ as well as ALP-nucleon couplings of the order of $g_{ann}^{(1)} sim 10^{-9}$, testing regions beyond TEXONO and Borexino limits.
Dark matter might be made of warm particles, such as sterile neutrinos in the keV mass range, which can decay into photons through mixing and are consequently detectable by X-ray telescopes. Axionlike particles (ALPs) are detectable by X-ray telescopes too when coupled to standard model particles and decay into photons in the keV range. Both particles could explain the unidentified 3.5 keV line and, interestingly, XENON1T observed an excess of electron recoil events most prominent at 2-3 keV. One explanation could be an ALPs origin, which is not yet excluded by X-ray constraints in an anomaly-free symmetry model in which the photon production is suppressed. We study the diffuse emission coming from the Galactic halo, and calculate the sensitivity of all-sky X-ray survey performed by eROSITA to identify a sterile neutrino or ALP dark matter. We estimate bounds on the mixing angle of the sterile neutrinos and coupling strength of the ALPs. After four years of data-taking by eROSITA, we expect to set stringent constraints, and in particular, we expect to firmly probe mixing angle $sin^2(2theta)$ up to nearly two orders magnitude below the best-fit value for explaining the unidentified 3.5 keV line. Moreover, with eROSITA, we will be able to probe the ALP parameter space of couplings to photons and electrons, and potentially confirm an ALP origin of the XENON1T excess.
Axionlike-particles (ALPs) are one promising type of dark matter candidate particle that may generate detectable effects on $gamma$-ray spectra other than the canonical weakly interacting massive particles. In this work we search for such oscillation effects in the spectra of supernova remnants caused by the photon-ALP conversion, using the Fermi Large Area Telescope data. Three bright supernova remnants, IC443, W44, and W51C, are analyzed. The inclusion of photon-ALP oscillations yields an improved fit to the $gamma$-ray spectrum of IC443, which gives a statistical significance of $4.2sigma$ in favor of such spectral oscillation. However, the best-fit parameters of ALPs ($m_{a}=6.6,{rm neV}$, $g_{agamma}=13.4 times 10^{-11},{rm GeV}^{-1}$) are in tension with the upper bound ($g_{agamma}< 6.6 times 10^{-11},{rm GeV}^{-1}$) set by the CAST experiment. It is difficult to explain the results using the systematic uncertainties of the flux measurements. We speculate that the irregularity displayed in the spectrum of IC443 may be due to the superposition of the emission from different parts of the remnant.
During a core-collapse supernova (SN), axionlike particles (ALPs) could be produced through the Primakoff process and subsequently convert into $gamma$ rays in the magnetic field of the Milky Way. We do not find evidence for such a $gamma$-ray burst in observations of extragalactic SNe with the Fermi Large Area Telescope (LAT). The SN explosion times are estimated from optical light curves and we find a probability of about $sim$90% that the LAT observed at least one SN at the time of the core collapse. Under the assumption that at least one SN was contained within the LAT field of view, we exclude photon-ALP couplings $gtrsim 2.6times10^{-11}$GeV$^{-1}$ for ALP masses $m_a lesssim 3times 10^{-10}$ eV, within a factor of $sim 5$ of previous limits from SN1987A.
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