Speaker
Description
We present constraints axion-like particles (ALPs) derived from 7.5 years of very-high-energy gamma-ray observations of the radio galaxy M87 with the High Altitude Water Cherenkov (HAWC) Observatory. ALPs are well-motivated dark matter candidates that can oscillate into photons in the presence of external magnetic fields — a phenomenon known as photon–ALP conversion — potentially producing characteristic spectral distortions in the gamma-ray spectra of extragalactic sources. Embedded within the strongly magnetized environment of the Virgo Cluster at a redshift of $z = 0.0044$, M87 provides an excellent laboratory for probing photon–ALP mixing at multi-TeV energies. We analyze the gamma-ray spectrum of M87 using a binned Poisson likelihood-ratio framework and compute photon survival probabilities with the gammaALPs software package, incorporating the stochastic nature of the magnetic field through an ensemble of 75 independent linear polarization realizations for each ALP candidate. Finding no statistically significant evidence for photon–ALP conversion, we derive $95\%$ confidence level exclusion regions in the ALP mass–coupling parameter space. Our results constrain photon–ALP couplings above $5\times10^{-12}$ GeV$^{-1}$ for ALP masses in the approximate range $10^{-8}-10^{-6}$ eV. These limits are consistent with, and complementary to, existing constraints obtained by other gamma-ray observatories.