Dark Photon Oscillations in Our Inhomogeneous Universe. (arXiv:2002.05165v1 [astro-ph.CO])

<a href="http://arxiv.org/find/astro-ph/1/au:+Caputo_A/0/1/0/all/0/1">Andrea Caputo</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Liu_H/0/1/0/all/0/1">Hongwan Liu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mishra_Sharma_S/0/1/0/all/0/1">Siddharth Mishra-Sharma</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ruderman_J/0/1/0/all/0/1">Joshua T. Ruderman</a>

A dark photon may kinetically mix with the ordinary photon, inducing

oscillations with observable imprints on cosmology. Oscillations are resonantly

enhanced if the dark photon mass equals the ordinary photon plasma mass, which

tracks the free electron number density. Previous studies have assumed a

homogeneous Universe; in this Letter, we introduce for the first time an

analytic formalism for treating resonant oscillations in the presence of

inhomogeneities of the photon plasma mass. We apply our formalism to determine

constraints from Cosmic Microwave Background photons oscillating into dark

photons, and from heating of the primordial plasma due to dark photon dark

matter converting into low-energy photons. Including the effect of

inhomogeneities demonstrates that prior homogeneous constraints are not

conservative, and simultaneously extends current experimental limits into a

vast new parameter space.

A dark photon may kinetically mix with the ordinary photon, inducing

oscillations with observable imprints on cosmology. Oscillations are resonantly

enhanced if the dark photon mass equals the ordinary photon plasma mass, which

tracks the free electron number density. Previous studies have assumed a

homogeneous Universe; in this Letter, we introduce for the first time an

analytic formalism for treating resonant oscillations in the presence of

inhomogeneities of the photon plasma mass. We apply our formalism to determine

constraints from Cosmic Microwave Background photons oscillating into dark

photons, and from heating of the primordial plasma due to dark photon dark

matter converting into low-energy photons. Including the effect of

inhomogeneities demonstrates that prior homogeneous constraints are not

conservative, and simultaneously extends current experimental limits into a

vast new parameter space.

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