  We study the decay width of the Higgs-boson $H\to gg$ up to order
$\alpha_s^5$ under the minimal momentum space subtraction scheme (mMOM-scheme).
To improve the accuracy of perturbative QCD prediction, we adopt the principle
of maximum conformality (PMC) to set its renormalization scales. A detailed
comparison of the total decay width and the separate decay widths at each
perturbative order before and after the PMC scale setting is presented. The PMC
adopts the renormalization group equation to fix the optimal scales of the
process. After the PMC scale setting, the scale-dependence for both the total
and the separate decay widths are greatly suppressed, and the convergence of
perturbative QCD series is improved. By taking the Higgs mass $M_H=125.09\pm
0.21\pm 0.11$ GeV, as recently given by the ATLAS and CMS collaborations, we
predict $\Gamma(H\to gg)|_{\rm mMOM, PMC} = 339.1\pm 1.7^{+4.0}_{-2.4}$ keV,
where the first error is for Higgs mass and the second error is the residual
scale dependence by varying the initial scale $\mu_r\in[M_H/2,4M_H]$.

High Energy Physics - Phenomenology