Walking signals inNf=8QCD on the lattice

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We investigate chiral and conformal properties of the lattice QCD with eight flavors (${N}_{f}=8$) through meson spectrum using the highly improved staggered quark (HISQ) action. We also compare our results with those of ${N}_{f}=12$ and ${N}_{f}=4$ which we study on the same systematics. We find that the decay constant ${F}_{\ensuremath{\pi}}$ of the pseudoscalar meson ``pion'' $\ensuremath{\pi}$ is nonzero, with its mass ${M}_{\ensuremath{\pi}}$ consistent with zero, both in the chiral limit extrapolation of the chiral perturbation theory. We also measure other quantities which we find are in accord with the $\ensuremath{\pi}$ data results: The $\ensuremath{\rho}$ meson mass is consistent with nonzero in the chiral limit, and so is the chiral condensate, with its value neatly coinciding with that from the Gell-Mann-Oakes-Renner relation in the chiral limit. Thus, our data for the ${N}_{f}=8$ QCD are consistent with the spontaneously broken chiral symmetry. Remarkably enough, while the ${N}_{f}=8$ data near the chiral limit are well described by the chiral perturbation theory, those for the relatively large fermion bare mass ${m}_{f}$ away from the chiral limit actually exhibit a finite-size hyperscaling relation, suggesting a large anomalous dimension ${\ensuremath{\gamma}}_{m}\ensuremath{\sim}1$. This implies that there exists a remnant of the infrared conformality, and suggests that a typical technicolor (``one-family model'') as modeled by the ${N}_{f}=8$ QCD can be a walking technicolor theory having an approximate scale invariance with large anomalous dimension ${\ensuremath{\gamma}}_{m}\ensuremath{\sim}1$.