We find that a holographic walking technicolor model has a limit ("conformal limit") where the techni-dilaton (TD) becomes a massless Nambu-Goldstone boson of the scale symmetry with its nonzero finite decay constant F φ = 0, which naturally realizes a light TD, say at 125 GeV, near the limit. In such a light TD case, we find that F φ is uniquely determined by the techni-pion decay constant Fπ independently of the holographic parameters: F φ /Fπ ≃ √ 2NTF, with NTF being the number of techni-fermions. We show that the holographic TD is consistent with a new boson at 125 GeV recently discovered at the LHC.

No abstract

We propose a scale-invariant chiral perturbation theory of the pseudo-Nambu-Goldstone bosons of chiral symmetry (pion π) as well as the scale symmetry (dilaton φ) for large N f QCD. The resultant dilaton mass M φ reads M (3 − γm)(1 + γm) · (π + (chiral log corrections), where m φ , mπ, γm, Fπ and F φ are the dilaton mass in the chiral limit, the pion mass, the mass anomalous dimension, and the decay constants of π and φ, respectively. The chiral extrapolation of the lattice data, when plotted as M 2 φ vs m 2 π , then simultaneously determines (m φ , F φ ) of the technidilaton in walking technicolor with γm ≃ 1. The chiral logarithmic corrections are explicitly given.Since the Higgs boson was discovered at the LHC [1], the next stage of particle physics will be to elucidate the dynamical origin of the Higgs boson, whose mass and coupling are free parameters within the Standard Model. One theory beyond the standard model is Walking Technicolor, which, based on the approximately scaleinvariant gauge dynamics, predicted a large anomalous dimension γ m ≃ 1 and a pseudo Nambu-Goldstone (NG) boson of the approximate scale invariance ("Technidilaton") as a light composite Higgs boson [2]. The technidilaton was actually shown to be consistent with current LHC data for the Higgs [3,4].A strongly coupled dynamics, walking technicolor would need fully nonperturbative calculations in order to make reliable estimates of the properties of the technidilaton and other composite particles to be compared with the upcoming high statistics data at LHC. There has been much work on the lattice in search for walking technicolor [5]. Among others, the LatKMI Collaboration [6] observed a flavor-singlet scalar meson lighter than the "pion" (corresponding to the NG boson in the chirally broken phase) in N f = 12 QCD -a theory shown [7] to be consistent with the chirally unbroken (conformal) phase on the same lattice setting. Such a light scalar might be a bound state generated only in the presence of the explicit fermion mass m f in the conformal phase. Still, it gives a good hint for the technidilaton signature in the walking theory, which should have a similar conformal dynamics, with the role of m f instead played by the dynamical mass of the fermion generated by spontaneous chiral symmetry breaking.Amazingly, LatKMI Collaboration also observed indications of a light flavor-singlet scalar with comparable mass to the pion in N f = 8 QCD [8] -a theory shown [9] to be walking, having both signals of spontaneous chiral symmetry breaking and a remnant of conformality. This should be a candidate for the technidilaton as a light composite Higgs boson in walking technicolor.However, walking technicolor makes sense only for vanishing fermion mass, m f ≡ 0, and hence the techinidilaton mass should be determined in the chiral limit. We would need an extrapolation formula for the dilaton mass in the same sense as the usual chiral perturbation theory (ChPT) [10] for the lattice data measured at nonzero m f to be extrapolated to the chiral limit.In t...

Walking technicolor predicts a light composite scalar, techni-dilaton, arising as a pseudo NambuGoldstone boson for the approximate scale symmetry spontaneously broken by techni-fermion condensation. We show that a light techni-dilaton with mass of around 125 GeV can explain presently observed excesses particularly in the di-photon decay channel at LHC.