A theory of extra radiation in the Universe

Kazunori Nakayama, Fuminobu Takahashi, Tsutomu T. Yanagida

Research output: Contribution to journalArticlepeer-review

56 Citations (Scopus)

Abstract

Recent cosmological observations, such as the measurement of the primordial 4He abundance, CMB, and large scale structure, give preference to the existence of extra radiation component, δNν>0. The extra radiation may be accounted for by particles which were in thermal equilibrium and decoupled before the big bang nucleosynthesis. Broadly speaking, there are two possibilities: (1) there are about 10 particles which have very weak couplings to the standard model particles and decoupled much before the QCD phase transition; (2) there is one or a few light particles with a reasonably strong coupling to the plasma and it decouples after the QCD phase transition. Focusing on the latter case, we find that a light chiral fermion is a suitable candidate, which evades astrophysical constraints. Interestingly, our scenario predicts a new gauge symmetry at TeV scale, and therefore may be confirmed at the LHC. As a concrete example, we show that such a light fermion naturally appears in the E6-inspired GUT.

Original languageEnglish
Pages (from-to)275-279
Number of pages5
JournalPhysics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
Volume697
Issue number4
DOIs
Publication statusPublished - 2011 Mar 14
Externally publishedYes

Keywords

  • Extra radiation
  • Grand unified theory

ASJC Scopus subject areas

  • Nuclear and High Energy Physics

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