A Higgslike Dilaton

TL;DR

The paper investigates whether the 125 GeV Higgs-like resonance could be a dilaton, the Goldstone boson of spontaneously broken scale invariance, within a partially composite framework. It develops a spurion-based effective theory that yields dilaton couplings to SM fields, showing that with $f$ close to the electroweak scale $v$ the couplings can resemble those of the SM Higgs, while the dilaton mass remains challenging to keep light relative to the dynamical scale $\\Lambda \\sim 4\\pi f$ without tuning. The authors explore naturalness through SUSY (3-2 model) and non-SUSY (Goldberger-Wise stabilized RS) examples, illustrating how a light dilaton can arise but often at the cost of tuning or suppressed couplings. They analyze collider implications, EWPT constraints, and the interplay of beta-function contributions, highlighting the conditions under which current LHC data could accommodate a dilaton. Overall, while a Higgs-like dilaton is a theoretically appealing possibility, realizing it without substantial tuning in non-supersymmetric theories remains difficult, and SUSY-based frameworks provide clearer naturalness paths.

Abstract

We examine the possibility that the recently discovered 125 GeV higgs like resonance actually corresponds to a dilaton: the Goldstone boson of scale invariance spontaneously broken at a scale f. Comparing to LHC data we find that a dilaton can reproduce the observed couplings of the new resonance as long as f ~ v, the weak scale. This corresponds to the dynamical assumption that only operators charged under the electroweak gauge group obtain VEVs. The more difficult task is to keep the mass of the dilaton light compared to the dynamical scale, Lambda ~ 4 pi f, of the theory. In generic, non-supersymmetric theories one would expect the dilaton mass to be similar to Lambda. The mass of the dilaton can only be lowered at the price of some percent level (or worse) tuning and/or additional dynamical assumptions: one needs to suppress the contribution of the condensate to the vacuum energy (which would lead to a large dilaton quartic coupling), and to allow only almost marginal deformations of the CFT.

Figures (2)

• Figure 1: Left: Constraints on the $v/f$ and $b_{UV,CFT}^{(3)} = b_{UV,CFT}^{(EM)}/2$ plane (shaded allowed regions) from experimental measurement at the $1\sigma$ CL of the rates $R_{incl., ZZ}$ (green), $R_{incl., \gamma \gamma}$ (orange), $R_{VH,bb}$ (blue), and EWPT at 99% CL (purple). The overlap region is shown in red. We have assumed $\gamma_i = 0$, and we recall that $c_{V, \sigma} = v/f$. Right: Same constraints in the $b_{UV,CFT}^{(EM)}$ and $b_{UV,CFT}^{(3)}$ plane fixing $v/f = 1$.
• Figure 2: Dilaton predictions for the rates $R_{incl., ZZ}$ (green line), $R_{incl., \gamma \gamma}$ (orange), and $R_{VH,bb}$ (blue) as a function of $b_{UV,CFT}^{(3)} = b_{UV,CFT}^{(EM)}/2$ for $v/f = 1$ (left panel) and $v/f = 0.8$ (right). Also shown as horizontal bands the current experimental intervals at $1\sigma$ CL (same color code).