Quark Condensate from Renormalization Group Optimized Spectral Density

Abstract

Our renormalization group consistent variant of optimized perturbation, RGOPT, is used to calculate the nonperturbative QCD spectral density of the Dirac operator and the related chiral quark condensate $⟨\bar{q}q⟩$, for $n_f=2$ and $n_f=3$ massless quarks. Sequences of approximations at two-, three-, and four-loop orders are very stable and give $⟨\bar{q}q{⟩}_{n_f=2}^{1/3}(2\mathrm{GeV})=-(0.833-0.845){\bar{\Lambda }}_2$, and $⟨\bar{q}q{⟩}_{n_f=3}^{1/3}(2\mathrm{GeV})=-(0.814-0.838){\bar{\Lambda }}_3$ where the range is our estimated theoretical error and ${\bar{\Lambda }}_{n_f}$ the basic QCD scale in the $\overline{\mathrm{MS}}$-scheme. We compare those results with other recent determinations (from lattice calculations and spectral sum rules).

arXiv comment5 pages, talk given at 18th International Conference in Quantum Chromodynamics (QCD 15) Montpellier, to appear in the proceedings

References in corpus (2)

• Review of lattice results concerning low energy particle physics
• MILC results for light pseudoscalars