Effective Theory of a Light Dilaton

TL;DR

This paper develops an effective theory for a light dilaton arising from strong conformal dynamics, analyzing its couplings to Standard Model particles and implications for electroweak symmetry breaking models.

Contribution

It constructs the effective dilaton theory near conformal symmetry breaking and evaluates the size of symmetry-violating corrections to its couplings.

Findings

Light dilaton mass can be naturally below the strong scale if the conformal-breaking operator is near marginal.

Corrections to dilaton couplings from conformal symmetry breaking are generally suppressed and controllable.

In some cases, symmetry-violating effects can dominate dilaton interactions, especially with marginal operators.

Abstract

We consider scenarios where strong conformal dynamics constitutes the ultraviolet completion of the physics that drives electroweak symmetry breaking. We show that in theories where the operator responsible for the breaking of conformal symmetry is close to marginal at the breaking scale, the dilaton mass can naturally lie below the scale of the strong dynamics. However, in general this condition is not satisfied in the scenarios of interest for electroweak symmetry breaking, and so the presence of a light dilaton in these theories is associated with mild tuning. We construct the effective theory of the light dilaton in this framework, and determine the form of its couplings to Standard Model states. We show that corrections to the form of the dilaton interactions arising from conformal symmetry violating effects are suppressed by the square of the ratio of the dilaton mass to the strong coupling scale, and are under good theoretical control. These corrections are generally subleading, except in the case of dilaton couplings to marginal operators, when symmetry violating effects can sometimes dominate. We investigate the phenomenological implications of these results for models of technicolor, and for models of the Higgs as a pseudo-Nambu-Goldstone boson, that involve strong conformal dynamics in the ultraviolet.