Holographic Techni-dilaton

Abstract

Techni-dilaton, a pseudo-Nambu-Goldstone boson of scale symmetry, was predicted long ago in the Scale-invariant/Walking/Conformal Technicolor (SWC-TC) as a remnant of the (approximate) scale symmetry associated with the conformal fixed point, based on the conformal gauge dynamics of ladder Schwinger-Dyson (SD) equation with non-running coupling. We study the techni-dilaton as a flavor-singlet bound state of techni-fermions by including the techni-gluon condensate (tGC) effect into the previous (bottom-up) holographic approach to the SWC-TC, a deformation of the holographic QCD with ${\gamma }_m\simeq 0$ by large anomalous dimension ${\gamma }_m\simeq 1$. With including a bulk scalar field corresponding to the gluon condensate, we first improve the Operator Product Expansion of the current correlators so as to reproduce gluonic $1/Q^4$ term both in QCD and SWC-TC. We find in QCD about $10\%$ (negative) contribution of gluon condensate to the $\rho$ meson mass. We also calculate the oblique electroweak $S$-parameter in the presence of the effect of the tGC and find that for the fixed value of $S$ the tGC effects dramatically reduce the flavor-singlet scalar (techni-dilaton) mass $M_{\mathrm{TD}}$ (in the unit of $F_{\pi }$), while the vector and axial-vector masses $M_{\rho }$ and $M_{a_1}$ are rather insensitive to the tGC, where $F_{\pi }$ is the decay constant of the techni-pion. If we use the range of values of tGC implied by the ladder SD analysis of the non-perturbative scale anomaly in the large $N_f$ QCD near the conformal window, the phenomenological constraint $S\simeq 0.1$ predicts the techni-dilaton mass $M_{\mathrm{TD}}\sim 600$ GeV which is within reach of LHC discovery.

28 pages, 11 eps files, typos corrected, references added, Fig.1 corrected, some discussions added, to be published in PRD

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• Conformal Barrier and Hidden Local Symmetry Constraints: Walking Technirhos in LHC Diboson Channels
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• Techni-dilaton as Dark Matter
• Analysis of techni-dilaton as a dark matter candidate
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