科研之友
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摘要
We study the discrete beta function of SU(3) gauge theory with N-f = 12 massless fermions in the fundamental representation. Using an nHYP-smeared staggered lattice action and an improved gradient flow running coupling (g) over tilde (2)(c) (L) we determine the continuum-extrapolated discrete beta function up to g(c)(2) approximate to 8.2. We observe an IR fixed point at g(star)(2) = 7.3 ((+8)(-2)) in the c = root 8t/L = 0.25 scheme, and g(star)(2) = 7.3((+6)(-3)) with c = 0.3, combining statistical and systematic uncertainties in quadrature. The systematic e ff ects we investigate include the stability of the (a = L) -> 0 extrapolations, the interpolation of (g) over tilde (2)(c) (L) as a function of the bare coupling, the improvement of the gradient flow running coupling, and the discretization of the energy density. In an appendix we observe that the resulting systematic errors increase dramatically upon combining smaller c less than or similar to 0.2 with smaller L <= 12, leading to an IR fixed point at g(star)(2) = 5.9(1.9) in the c = 0.2 scheme, which resolves to g(star)(2) = 6.9((+6)(-1)) upon considering only L >= 16. At the IR fi xed point we measure the leading irrelevant critical exponent to be gamma(star)(g) = 0.26(2), comparable to perturbative estimates.
- 出版日期2018-2-21
