Light flavor-singlet scalars and walking signals in Nf=8 QCD on the lattice
Light flavor-singlet scalars and walking signals in Nf=8 QCD on the lattice
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DOI：
10.1103/physrevd.96.014508
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发表时间：
2016-10
影响因子：
5
通讯作者：
Y. Aoki;T. Aoyama;E. Bennett;M. Kurachi;T. Maskawa;K. Miura;K. Nagai;H. Ohki;E. Rinaldi
中科院分区：
文献类型：
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作者：
Y. Aoki;T. Aoyama;E. Bennett;M. Kurachi;T. Maskawa;K. Miura;K. Nagai;H. Ohki;E. Rinaldi
基于改进的交错夸克作用量，我们对Nf=8的QCD进行了格点模拟，证实了我们以前的观察，即一个像π介子一样轻的味单重标量介子（记为σ）和各种通过低位谱的“行走信号”，具有更高的统计量，更小的费米子质量mf和更大的体积。我们测量Mπ、Fπ、Mρ、Ma 0、Ma 1、Mb 1、MN、Mσ、Fσ、M σ和弦张力（直接测量和通过盖尔曼-奥克斯-伦纳关系测量）。这些数据与手征对称性的自发破缺相一致，与先前的结果一致：在较小的mf区域内，Mπ的量的比率向手征极限单调增加，类似于Nf=4 QCD，与Nf=12 QCD形成鲜明对比，其中比率变得平坦。我们对手征微扰理论进行了拟合，手征极限外推中发现的Fπ值急剧减少到以前结果的约2/3，表明该理论更接近共形窗口。事实上，每个量服从各自的超标度关系在一个更广泛的MF区域相比，早期的作品。超标度关系大致上与反常维数γm <$1的普适值保持一致，但与前面的结果一样，Mπ的反常维数γm <$0. 6是一个显著的例外，这反映了上述比值向手征极限的增长。这是Nf=8的一个显著特征（行走信号），不像Nf=4，它根本没有超标度关系，也不像Nf=12 QCD，它表现出普遍的超标度。在每个mf区域定义的Mπ的有效γm <$γm（mf）在手征极限附近有向1增长的趋势，这符合南武-戈德斯通玻色子的性质，而在Nf=12的QCD情况下，它几乎是常数。我们进一步证实了以前在所研究的mf区域中观测到的质量与π介子相当的光σ。在用手征微扰理论和简单的线性拟合对σ质量进行手征极限外推时，我们发现σ质量的值与125 GeV的Higgs玻色子的值在误差范围内是一致的。我们的结果表明，该理论是一个很好的步行人工色模型的候选者，具有反常的γm 1维和一个轻味单重标量介子作为技术子，它可以与Nf=8单族模型中的125 GeV复合Higgs相鉴别.
Based on the highly improved staggered quark action, we perform lattice simulations of Nf=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 mf, and larger volumes. We measure Mπ, Fπ, Mρ, Ma0, Ma1, Mb1, MN, Mσ, Fσ, ⟨ψ¯ψ⟩ (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 Mπ monotonically increase in the smaller mf region towards the chiral limit similarly to Nf=4 QCD, in sharp contrast to Nf=12 QCD where the ratios become flattened. We perform fits to chiral perturbation theory, with the value of Fπ 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 a more extensive mf region compared with earlier works. The hyperscaling relation holds with roughly a universal value of the anomalous dimension, γm≃1, with the notable exception of Mπ with γm≃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 Nf=8, unlike either Nf=4, which has no hyperscaling relation at all, or Nf=12 QCD, which exhibits universal hyperscaling. The effective γm≡γm(mf) of Mπ defined for each mf 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 Nf=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 mf 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. Our results suggest that the theory could be a good candidate for walking technicolor model, having anomalous dimension γm≃1 and a light flavor-singlet scalar meson as a technidilaton, which can be identified with the 125 GeV composite Higgs in the Nf=8 one-family model.