Case for dark radiation

Archidiacono, Maria, Calabrese, Erminia ORCID: https://orcid.org/0000-0003-0837-0068 and Melchiorri, Alessandro 2011. Case for dark radiation. Physical Review D 84 (12) , 123008. 10.1103/PhysRevD.84.123008

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Abstract

Combined analyses of recent cosmological data are showing interesting hints for the presence of an extra relativistic component, coined dark radiation. Here, we perform a new search for dark radiation, parametrizing it with an effective number of relativistic degrees of freedom parameter, Neff. We show that the cosmological data we considered are clearly suggesting the presence of an extra relativistic component with Neff ¼ 4:08þ0:71 �0:68 at 95% C.L.. Performing an analysis on dark radiation sound speed ceff and viscosity cvis parameters, we found c2 eff ¼ 0:312 0:026 and c2 vis ¼ 0:29þ0:21 �0:16 at 95% C.L., consistent with the expectations of a relativistic free streaming component (c2 eff ¼ c2vis ¼ 1=3). Assuming the presence of 3 relativistic neutrinos, we constrain the extra relativistic component with NS� ¼ 1:10þ0:79 �0:72 and c2 eff ¼0:24þ0:08 �0:13 at 95% C.L. while c2 vis results as unconstrained. Assuming a massive neutrino component, we obtain further indications for dark radiation with NS � ¼ 1:12þ0:86 �0:74 at 95% C.L..

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Physics and Astronomy
Subjects:	Q Science > QB Astronomy
Publisher:	American Physical Society
ISSN:	2470-0010
Date of First Compliant Deposit:	9 October 2017
Date of Acceptance:	16 September 2011
Last Modified:	08 May 2023 04:58
URI:	https://orca.cardiff.ac.uk/id/eprint/105337

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