Light scalar at LHC: the Higgs or the dilaton?

TL;DR

This paper explores the possibility that a scalar observed at colliders could be a pseudo-dilaton from conformal symmetry breaking, not just the Standard Model Higgs, and discusses how to distinguish these scenarios.

Contribution

It proposes new methods to differentiate a pseudo-dilaton from a Higgs boson based on self-interactions and couplings, especially in nearly conformal EWSB models.

Findings

Self-interactions of the scalar differ depending on the conformal sector's operators.

Enhanced couplings to massless gauge bosons can indicate a dilaton.

Dilaton pair production at colliders can probe conformal symmetry breaking.

Abstract

It is likely that the LHC will observe a color- and charge-neutral scalar whose decays are consistent with those of the Standard Model (SM) Higgs boson. The Higgs interpretation of such a discovery is not the only possibility. For example, electroweak symmetry breaking (EWSB) could be triggered by a spontaneously broken, nearly conformal sector. The spectrum of states at the electroweak scale would then contain a narrow scalar resonance, the pseudo-Goldstone boson of conformal symmetry breaking, with Higgs-like properties. If the conformal sector is strongly coupled, this pseudo-dilaton may be the only new state accessible at high energy colliders. We discuss the prospects for distinguishing this mode from a minimal Higgs boson at the LHC and ILC. The main discriminants between the two scenarios are (1) cubic self-interactions and (2) a potential enhancement of couplings to massless SM gauge bosons. A particularly interesting situation arises when the scale f of conformal symmetry breaking is approximately the electroweak scale v~246 GeV. Although in this case the LHC may not be able to tell apart a pseudo-dilaton from the Higgs boson, the self-interactions differ in a way that depends only on the scaling dimension of certain operators in the conformal sector. This opens the possibility of using dilaton pair production at future colliders as a probe of EWSB induced by nearly conformal new physics.