Abstract
Recently it has been noticed that the Fermi-LAT data of gamma-rays from some galactic pulsars and supernova remnants reveal spectral modulations that might be explained by the conversion of photons to ALPs (axion-like particles) induced by the conventional ALP coupling to photon in the presence of galactic magnetic fields. However the corresponding ALP mass and coupling are in a severe tension with the observational constraints from CAST, SN1987A, and other gamma-ray observations. Motivated by this, we examine an alternative possibility that those spectral modulations are explained by other type of ALP coupling involving both the ordinary photon and a massless dark photon, when nonzero background dark photon gauge fields are assumed. We find that our scheme results in oscillations among the photon, ALP, and dark photon, which can explain the gamma-ray spectral modulations of galactic pulsars or supernova remnants, while satisfying the known observational constraints.
Highlights
Light axionlike particles (ALPs) and hidden Uð1Þ gauge bosons have been widely discussed as well-motivated candidates for physics beyond the Standard Model of particle physics [1]
It has been noticed that the Fermi-LAT data of gamma-rays from some galactic pulsars and supernova remnants reveal spectral modulations that might be explained by the conversion of photons to ALPs induced by the conventional ALP coupling to photon in the presence of galactic magnetic fields
We find that our scheme results in oscillations among the photon, ALP, and dark photon, which can explain the gamma-ray spectral modulations of galactic pulsars or supernova remnants, while satisfying the known observational constraints
Summary
Light axionlike particles (ALPs) and hidden Uð1Þ gauge bosons have been widely discussed as well-motivated candidates for physics beyond the Standard Model of particle physics [1]. A key ingredient of our scenario is the existence of a background dark photon gauge fields hBXi and/or hEXi with a strength comparable to (or bigger than) the galactic magnetic fields ∼1 μG and a coherent length longer than the typical galactic size ∼1 kpc If they were generated in the early universe, such background dark photon gauge fields may result in a dangerous distortion of CMB due to the resonant conversion of CMB photons to axions, which would occur when the effective photon mass mγðtÞ in the early universe crosses the ALP mass ma [13,14,15].
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