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Title: Light flavor-singlet scalars and walking signals in N f = 8 QCD on the lattice

Based on the highly improved staggered quark action, we perform in this paper lattice simulations of N f = 8 QCD and confirm our previous observations, both of a flavor-singlet scalar meson (denoted as σ) as light as the pion and of various “walking signals” through the low-lying spectra, with higher statistics, smaller fermion masses m f, and larger volumes. We measure M π, F π, M ρ, M a0, M a1, M b1, M N, M σ, F σ, (φφ) (both directly and through the Gell-Mann-Oakes-Renner relation), and the string tension. The data are consistent with the spontaneously broken phase of the chiral symmetry, in agreement with the previous results: Ratios of the quantities to M π monotonically increase in the smaller m f region towards the chiral limit similarly to N f = 4 QCD, in sharp contrast to N f = 12 QCD where the ratios become flattened. We perform fits to chiral perturbation theory, with the value of F π found in the chiral limit extrapolation reduced dramatically to roughly 2/3 of the previous result, suggesting the theory is much closer to the conformal window. In fact, each quantity obeys the respective hyperscaling relation throughout amore » more extensive m f region compared with earlier works. The hyperscaling relation holds with roughly a universal value of the anomalous dimension, γ m ≃ 1, with the notable exception of M π with γ m ≃ 0.6 as in the previous results, which reflects the above growing up of the ratios towards the chiral limit. This is a salient feature (walking signal) of N f = 8, unlike either N f = 4, which has no hyperscaling relation at all, or N f = 12 QCD, which exhibits universal hyperscaling. The effective γ m Ξ γ m(m f) of M π defined for each m f region has a tendency to grow towards unity near the chiral limit, in conformity with the Nambu-Goldstone boson nature, as opposed to the case of N f = 12 QCD where it is almost constant. We further confirm the previous observation of the light σ with mass comparable to the pion in the studied m f region. In a chiral limit extrapolation of the σ mass using the dilaton chiral perturbation theory and also using the simple linear fit, we find the value consistent with the 125 GeV Higgs boson within errors. Finally, our results suggest that the theory could be a good candidate for walking technicolor model, having anomalous dimension γ m ≃ 1 and a light flavor-singlet scalar meson as a technidilaton, which can be identified with the 125 GeV composite Higgs in the N f = 8 one-family model.« less
 [1] ;  [2] ;  [3] ;  [4] ;  [2] ;  [5] ;  [2] ;  [6] ;  [7] ;  [4] ;  [2] ;  [8]
  1. High Energy Accelerator Research Organization (KEK), Tsukuba (Japan); Brookhaven National Lab. (BNL), Upton, NY (United States)
  2. Nagoya Univ. (Japan)
  3. Swansea Univ. (United Kingdom)
  4. High Energy Accelerator Research Organization (KEK), Tsukuba (Japan)
  5. Aix-Marseille Univ., Marseille (France); Nagoya Univ. (Japan)
  6. Brookhaven National Lab. (BNL), Upton, NY (United States)
  7. Brookhaven National Lab. (BNL), Upton, NY (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  8. Univ. of Tsukuba (Japan)
Publication Date:
Report Number(s):
Journal ID: ISSN 2470-0010; R&D Project: PO-3
Grant/Contract Number:
AC52-07NA27344; SC0012704; 22224003; 16K05320; 15K05049; 16H06002; 25800138; 25800139; 15K17644; 25105011; ANR-11-LABX-0060; ANR-11-IDEX-0001-02
Accepted Manuscript
Journal Name:
Physical Review D
Additional Journal Information:
Journal Volume: 96; Journal Issue: 1; Journal ID: ISSN 2470-0010
American Physical Society (APS)
Research Org:
Brookhaven National Lab. (BNL), Upton, NY (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); High Energy Accelerator Research Organization (KEK), Tsukuba (Japan); Nagoya Univ. (Japan); Aix-Marseille Univ., Marseille (France)
Sponsoring Org:
USDOE; Japan Society for the Promotion of Science (JSPS); Ministry of Education, Culture, Sports, Science and Technology (MEXT) (Japan); National Agency for Research (ANR) (France)
Contributing Orgs:
LatKMI Collaboration
Country of Publication:
United States
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; dynamical symmetry breaking models; extensions of Higgs sector; extensions of gauge sector; lattice field theory; nonperturbative effects in field theory; lattice gauge theory; particles & fields
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1371805