Right-handed neutrinos as the dark radiation: Status and forecasts for the LHC

doi:10.1016/j.physletb.2012.12.019

Physics Letters B

Volume 718, Issues 4–5, 29 January 2013, Pages 1162-1165

https://doi.org/10.1016/j.physletb.2012.12.019 Get rights and content

Abstract

Precision data from cosmology (probing the CMB decoupling epoch) and light-element abundances (probing the BBN epoch) have hinted at the presence of extra relativistic degrees of freedom, the so-called “dark radiation.” We present a model independent study to account for the dark radiation by means of the right-handed partners of the three, left-handed, standard model neutrinos. We show that milli-weak interactions of these Dirac states (through their coupling to a TeV-scale $Z^{'}$ gauge boson) may allow the $ν_{R}$ ʼs to decouple much earlier, at a higher temperature, than their left-handed counterparts. If the $ν_{R}$ ʼs decouple during the quark–hadron crossover transition, they are considerably cooler than the $ν_{L}$ ʼs and contribute less than 3 extra “equivalent neutrinos” to the early Universe energy density. For decoupling in this transition region, the $3 ν_{R}$ generate $Δ N_{ν} = 3 {(T_{ν_{R}} / T_{ν_{L}})}^{4} < 3$ , extra relativistic degrees of freedom at BBN and at the CMB epochs. Consistency with present constraints on dark radiation permits us to identify the allowed region in the parameter space of $Z^{'}$ masses and couplings. Remarkably, the allowed region is within the range of discovery of LHC14.

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After this work was finished a paper appeared on the arXiv with a comprehensive study on dark radiation of $E_{6}$ models [45]. Our results are completely consistent with those of Ref. [45].

Acknowledgements

We thank the Galileo Galilei Institute for Theoretical Physics for the hospitality and the INFN for partial support during the completion of this work. L.A.A. is supported by the U.S. National Science Foundation (NSF) under CAREER Grant PHY-1053663. H.G. is supported by NSF Grant PHY-0757959. G.S. is supported by the Department of Energy (DOE) Grant DE-FG02-91ER40690. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not

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Right-handed neutrinos as the dark radiation: Status and forecasts for the LHC

Abstract

Section snippets

Note added

Acknowledgements

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Phys. Lett. B

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Nucl. Phys. B

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Phys. Lett. B

Phys. Rev. D

Phys. Rev. Lett.

Phys. Rev. D

Phys. Rev. D

Astrophys. J. Suppl.

Astrophys. J.

Astrophys. J.

Mon. Not. Roy. Astron. Soc.

Astrophys. J.

JCAP

Astrophys. J.

JCAP

Phys. Rev. D