Collider Signatures of Goldstone Bosons

TL;DR

This paper explores the collider signatures of Goldstone bosons from a global U(1) symmetry, their potential role in explaining deviations in N_eff, and possible detection at the LHC through specific decay channels.

Contribution

It provides detailed analysis of experimental constraints and proposes a novel collider signature involving Higgs decays into Goldstone bosons and pions.

Findings

Scalar ecays into pions with ~1% branching ratio

Collider signature involves Higgs production and decay into Goldstone bosons and pions

Parameter space where ecays are detectable at LHC

Abstract

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 N_eff, which has been reported persistently 1 \sigma 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 $\sigma$ and suggest a possible collider signature at the Large Hadron Collider (LHC). In some corners of the parameter space, the scalar field \sigma 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 q q'-bar -> H W, followed by H -> \sigma \sigma -> (\pi\pi) (\alpha\alpha), where \alpha is the Goldstone boson.