Limits on dark radiation, early dark energy, and relativistic degrees of freedom

Journal Article · Wed Jun 15 00:00:00 EDT 2011 · Physical Review. D, Particles Fields

DOI:https://doi.org/10.1103/PHYSREVD.83.123504· OSTI ID:21502714

Calabrese, Erminia; Melchiorri, Alessandro ^[1]; Huterer, Dragan ^[2]; Linder, Eric V ^[3]; Pagano, Luca ^[4]

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1. Physics Department and INFN, Universita' di Roma ''La Sapienza'', Ple Aldo Moro 2, 00185, Rome (Italy)
2. Department of Physics, University of Michigan, 450 Church St, Ann Arbor, Michigan 48109 (United States)
3. Berkeley Lab and University of California, Berkeley, California 94720, USA. (United States)
4. Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena California 91109 (United States)

Recent cosmological data analyses hint at the presence of an extra relativistic energy component in the early universe. This component is often parametrized as an excess of the effective neutrino number N{sub eff} over the standard value of 3.046. The excess relativistic energy could be an indication for an extra (sterile) neutrino, but early dark energy and barotropic dark energy also contribute to the relativistic degrees of freedom. We examine the capabilities of current and future data to constrain and discriminate between these explanations, and to detect the early dark energy density associated with them. We find that while early dark energy does not alter the current constraints on N{sub eff}, a dark radiation component, such as that provided by barotropic dark energy models, can substantially change current constraints on N{sub eff}, bringing its value back to agreement with the theoretical prediction. Both dark energy models also have implications for the primordial mass fraction of Helium Y{sub p} and the scalar perturbation index n{sub s}. The ongoing Planck satellite mission will be able to further discriminate between sterile neutrinos and early dark energy.

• OSTI ID: 21502714
• Journal Information: Physical Review. D, Particles Fields, Vol. 83, Issue 12; Other Information: DOI: 10.1103/PhysRevD.83.123504; (c) 2011 American Institute of Physics; ISSN 0556-2821
• Country of Publication: United States
• Language: English

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