Effective theory of a light dilaton

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.

Radion/dilaton-Higgs mixing phenomenology in light of the LHC

“…3 Radion-Higgs mixing Light radion/dilaton phenomenology and mixing with an IR-brane localized Higgs has been studied extensively in the literature [10][11][12][13][14][15]. It has been found that current LHC measurements, in particular of the Higgs mass and signal strengths, already put significant constraints on the parameter space of these models [18][19][20].…”

Higgs phenomenology in the Minimal Dilaton Model after Run I of the LHC

“…Since the first hint of the Higgs-like boson at the LHC was uncovered at the end of 2011, the compatibility of the dilaton with the data has been extensively discussed [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35]. For example, in [23][24][25][26][27][28][29] the traditional dilaton models were compared with models including Higgs boson, and the techni-dilaton was shown to be able to explain the signals well [30][31][32][33][34][35].…”

The minimal flavour violating axion

“…In order to reproduce the expected value of the EW VEV, v ≡ 245 GeV fixed through the W gauge boson mass, it is then necessary to invoke a large value of the Higgs quartic coupling λ, describing in this way a strongly interacting scenario with a non-linearly realised EWSB mechanism. This is an intriguing possibility, especially considering the recent interest in non-SM descriptions of the Higgs sector, such as composite Higgs models [87][88][89][90][91][92][93][94][95], dilaton models [96][97][98][99][100][101][102][103], or general effective Lagrangians [104][105][106][107][108][109][110][111][112][113][114][115][116][117][118][119][120][121]. In this letter, however, the traditional EWSB mechanism will be considered, and this requires to invoke a fine tuning: either there is cancellation between µ 2 and λ HΦ v 2 Φ , or λ HΦ is artificially small.…”