Cosmological origin of anomalous radio background

Abstract

The ARCADE 2 collaboration has reported a significant excess in the isotropic radio background, whose homogeneity cannot be reconciled with clustered sources. This suggests a cosmological origin prior to structure formation. We investigate several potential mechanisms and show that injection of relativistic electrons through late decays of a metastable particle can give rise to the observed excess radio spectrum through synchrotron emission. However, constraints from the cosmic microwave background (CMB) anisotropy, on injection of charged particles and on the primordial magnetic field, present a challenge. The simplest scenario is with a >~ 9 GeV particle decaying into e+e- at a redshift of z ~ 5, in a magnetic field of ~ 5 microgauss, which exceeds the CMB B-field constraints, unless the field was generated after decoupling. Decays into exotic millicharged particles can alleviate this tension, if they emit synchroton radiation in conjunction with a sufficiently large background magnetic field of a dark U(1)' gauge field.

arXiv comment13 pages, 7 figures; v3: minor clarifications, published version; v2: errors corrected (only synchrotron emission, not Compton, gives observed spectrum), extensive revision. Qualitative conclusions unchanged

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• Constraints on dark matter annihilation from CMB observations before Planck
• The isotropic radio background revisited
• Absolute Calibration of Diffuse Radio Surveys at 45 and 150 MHz
• A Stimulating Explanation of the Extragalactic Radio Background
• The Anisotropy of the Extragalactic Radio Background from Dark Matter Annihilation
• Relic neutrino decay solution to the excess radio background
• Note on the dark matter explanation of the ARCADE excess and AMS data
• Primordial black holes as dark matter candidates: Multi-frequency constraints from cosmic radiation backgrounds
• Disentangling the anisotropic radio sky: Fisher forecasts for 21cm arrays
• Impact of conversion-driven processes on singlet-doublet Majorana dark matter relic