摘要
Recently Weinberg suggested that Goldstone bosons arising from the spontaneous breakdown of some global hidden symmetries can interact weakly in the early Universe and account for a fraction of the effective number of neutrino species Neff, which has been reported persistently 1σ away from its expected value of three. In this work, we study in some details a number of experimental constraints on this interesting idea based on the simplest possibility of a global U(1), as studied by Weinberg. We work out the decay branching ratios of the associated light scalar field σ and suggest a possible collider signature at the Large Hadron Collider. In some corners of the parameter space, the scalar field σ can decay into a pair of pions with a branching ratio of order O(1)% while the rest is mostly a pair of Goldstone bosons. The collider signature would be gluon fusion into the standard model Higgs boson gg→H or associated production with a W gauge boson qq̄′→HW, followed by H→σσ→(ππ) (αα) where α is the Goldstone boson. © 2014 American Physical Society.