Walking signals in Nf=8 QCD on the lattice

Abstract

We investigate chiral and conformal properties of the lattice QCD with eight flavors (Nf=8) through meson spectrum using the Highly Improved Staggered Quark (HISQ) action. We also compare our results with those of Nf=12 and Nf=4 which we study on the same systematics. We find that the decay constant F_pi of the pseudoscalar meson "pion" is non-zero, with its mass M_pi consistent with zero, both in the chiral limit extrapolation of the chiral perturbation theory (ChPT). We also measure other quantities which we find are in accord with the pi data results: The rho meson mass is consistent with non-zero 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 Nf=8 QCD are consistent with the spontaneously broken chiral symmetry. Remarkably enough, while the Nf=8 data near the chiral limit are well described by the ChPT, 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 gamma_m ~ 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 Nf=8 QCD can be a walking technicolor theory having an approximate scale invariance with large anomalous dimension gamma_m ~ 1.

26 pages, 28 figures. References added. A version to be published in Phys.Rev.D

References in corpus (9)

• Highly Improved Staggered Quarks on the Lattice, with Applications to Charm Physics
• Scaling studies of QCD with the dynamical HISQ action
• The physics of eight flavours
• Nearly conformal gauge theories in finite volume
• The infrared dynamics of Minimal Walking Technicolor
• Running coupling constant of ten-flavor QCD with the Schrödinger functional method
• Holographic techni-dilaton at 125 GeV
• Lattice study of infrared behaviour in SU(3) gauge theory with twelve massless flavours
• Lattice Monte-Carlo study of pre-conformal dynamics in strongly flavoured QCD in the light of the chiral phase transition at finite temperature

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