Collider signatures of Goldstone bosons

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.