Constraints on axion-like particles with different magnetic field models from the PKS 2155-304 energy spectrum
Axion-like particles (ALPs) are a promising kind of dark matter candidate particle that are predicted to couple with photons in the presence of magnetic fields. The oscillations between photons and ALPs traveling in the magnetic fields have been used to constrain ALP properties. In this work, we obtain some new constraints on the ALP mass m a and the photon-ALP coupling constant g with two different magnetic field models through TeV photons from PKS 2155-304. The first is the discrete-φ model in which the magnetic field has the orientation angle φ that changes discretely and randomly from one coherent domain to the next, and the second is the linearly-continuous-φ model in which the magnetic field orientation angle φ varies continuously across neighboring coherent domains. For the discrete-φ model, we can obtain the best constraints on the ALP mass m 1 = m a/(1 neV) = 0.1 and on the photon-ALP coupling constant g 11 = g/(10-11 GeV-1) = 5. The reasonable range of the ALP mass m 1 is 0.08 ∼ 0.2 when g 11 = 5, and the only reasonable value of the photon-ALP coupling constant is g 11 = 5 when m 1 = 0.1. For the linearly-continuous-φ model, we can obtain the best constraints on the ALP mass m 1 = 0.1 and on the photon-ALP coupling constant g 11 = 0.7. The reasonable range of the ALP mass m 1 is 0.05 ∼ 0.4 when g 11 = 0.7, and the reasonable range of the photon-ALP coupling constant g 11 is 0.5 ∼ 1 when m 1 = 0.1. All of the results are consistent with the upper bound (g < 6.6 × 10-11 GeV-1, i.e., g 11 < 6.6) set by the CAST experiment.