Constraints on Axions and Axion-like Particles from Fermi Large Area Telescope Observations of Neutron Stars

ORAL

Abstract

We present constraints on the nature of axions and axion--like particles (ALPs) by analyzing gamma--ray data from neutron stars using the Fermi Large Area Telescope. In addition to axions solving the strong CP problem of particle physics, axions and ALPs are also possible dark matter candidates. We investigate axions and ALPs produced by nucleon--nucleon bremsstrahlung within neutron stars. We derive a phenomenological model for the gamma--ray spectrum arising from axion decays. By analyzing 5 years of gamma-ray data (between 60 MeV and 200 MeV) for a sample of 4 nearby neutron stars, we do not find evidence for an axion or ALP signal, thus we obtain a combined 95\% confidence level upper limit on the axion mass of 5.6$\times 10^{-2}$ eV, which corresponds to a lower limit for the Peccei-Quinn scale $f_a$ of 1.07$\times 10^8$ GeV. Our constraints are more stringent than previous results probing the same physical process, and are competitive with results probing axions and ALPs by different mechanisms.

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Authors

  • Bijan Berenji

    California State University, Los Angeles

  • Chi-Yu Hu

    University of California - Berkeley, National Institute for Materials Science, Caifornia State University, Long Beach, University of Michigan, Stockholm University, California State University, Long Beach, Utrecht University, Carl von Ossietzky University of Oldenburg, Germany, Hartnell Community College, Department of Physics, Stockholm University, GRAPPA, University of Amsterdam, Paul Scherrer Institute, Switzerland, California State University, Fresno, California State University Long Beach, Cal State Univ- Long Beach, University of Nevada, Reno, University of Rogensberg, Germany, Tribhuvan University, Nepal, University of Victoria and Perimeter Institute for Theoretical Physics, Institute of Physics, Jagiellonian University, Helmholtz Institute Mainz, Johannes Gutenberg University, Physics Department of the University of Nevada, Reno, Universita del Sannio, Cal Tech, California State University, Los Angeles, Univ of California - San Diego, UC Berkeley, Lawrence Livermore National Laboratory, Department of Physics & Astronomy, University of California, Irvine 92617, Department of Chemistry and of Physics & Astronomy, University of California, Irvine 92617, SLAC National Laboratory, Humboldt State University, Physics Department, University of Nevada, Reno, Univ of California - Merced

  • Chi-Yu Hu

    University of California - Berkeley, National Institute for Materials Science, Caifornia State University, Long Beach, University of Michigan, Stockholm University, California State University, Long Beach, Utrecht University, Carl von Ossietzky University of Oldenburg, Germany, Hartnell Community College, Department of Physics, Stockholm University, GRAPPA, University of Amsterdam, Paul Scherrer Institute, Switzerland, California State University, Fresno, California State University Long Beach, Cal State Univ- Long Beach, University of Nevada, Reno, University of Rogensberg, Germany, Tribhuvan University, Nepal, University of Victoria and Perimeter Institute for Theoretical Physics, Institute of Physics, Jagiellonian University, Helmholtz Institute Mainz, Johannes Gutenberg University, Physics Department of the University of Nevada, Reno, Universita del Sannio, Cal Tech, California State University, Los Angeles, Univ of California - San Diego, UC Berkeley, Lawrence Livermore National Laboratory, Department of Physics & Astronomy, University of California, Irvine 92617, Department of Chemistry and of Physics & Astronomy, University of California, Irvine 92617, SLAC National Laboratory, Humboldt State University, Physics Department, University of Nevada, Reno, Univ of California - Merced