Matching QCD and heavy-quark effective theory heavy-light currents at two loops and beyond

Oct, 1994
25 pages
Published in:
  • Phys.Rev.D 52 (1995) 4082-4098
e-Print:
Report number:
  • OUT-4102-52

Citations per year

1994200220102018202502468101214
Abstract:
Heavy--light QCD currents are matched with HQET currents at two loops and leading order in 1/m1/m. A single formula applies to all current matchings. As a by--product, a master formula for the two--loop anomalous dimension of the QCD current qˉγ [μ1γ μn]q\bar{q}\gamma~{[\mu_1}\ldots\gamma~{\mu_n]}q is obtained, yielding a new result for the tensor current. The dependence of matching coefficients on γ5\gamma_5 prescriptions is elucidated. Ratios of QCD matrix elements are obtained, independently of the three--loop anomalous dimension of HQET currents. The two--loop coefficient in fB /fB=12αs(mb)/3πKbαs 2/π 2+O(αs 3,1/mb)f_{{\rm B}~*}/f_{\rm B} =1-2\alpha_{\rm s}(m_b)/3\pi-K_b\alpha_{\rm s}~2/\pi~2 +{\rm O}(\alpha_{\rm s}~3,1/m_b) is Kb=8312+481π 2+227π 2log219ζ(3)1954Nl+Δc=6.37+ΔcK_b=\frac{83}{12}+\frac{4}{81}\pi~2+\frac{2}{27}\pi~2\log2-\frac19\zeta(3) -\frac{19}{54}N_l+\Delta_c=6.37+\Delta_c with Nl=4N_l=4 light flavours, and a correction, Δc=0.18±0.01\Delta_c=0.18\pm0.01, that takes account of the non--zero ratio mc/mb=0.28±0.03m_c/m_b=0.28\pm0.03. Fastest apparent convergence would entail αs(μ)\alpha_{\rm s}(\mu) at μ=370\mu=370MeV. ``Naive non--abelianization'' of large--NlN_l results, via NlNl332N_l\to N_l-\frac{33}{2}, gives reasonable approximations to exact two--loop results. All--order results for anomalous dimensions and matching coefficients are obtained at large β0=1123Nl\beta_0=11-\frac23N_l. Consistent cancellation between infrared-- and ultraviolet--renormalon ambiguities is demonstrated.
  • quark: current
  • quark: flavor
  • quark: mass
  • mass: quark
  • expansion: mass
  • mass: expansion
  • renormalization
  • quantum chromodynamics
  • HQET model
  • correction: higher-order