Dark Radiation Emerging After Big Bang Nucleosynthesis?

Abstract

We show how recent data from observations of the cosmic microwave background may suggest the presence of additional radiation density which appeared after big bang nucleosynthesis. We propose a general scheme by which this radiation could be produced from the decay of non-relativistic matter, we place constraints on the properties of such matter, and we give specific examples of scenarios in which this general scheme may be realized.

Comments: v3: 5 pages, 1 figure. References added, typos corrected, notation changed throughout. v2: 5 pages, 1 figure. Reformatted, references added, acknowledgments updated, effect of radiation on CMB clarified. v1: 11 pages, 1 figure