Sep 9 – 13, 2019
Europe/Zurich timezone

## Quark condensate and spectral density from renormalization group optimized perturbation

Sep 12, 2019, 5:30 PM
25m
Chambre du Trésorier

### Speaker

Jean-Loic Kneur (Univ. Montpellier)

### Description

Our renormalization group consistent version of optimized perturbation, RGOPT, had been used to calculate the nonperturbative QCD spectral density of the Dirac operator and the related chiral quark condensate $\langle \bar q q \rangle$, for $n_f=2$ and $n_f=3$ massless quarks. Sequences of approximations at two-, three-, and four-loop orders gave stable parameter-free determinations
$\langle\bar q q\rangle^{1/3}_{n_f=2}(2\, {\rm GeV}) = -(0.833-0.845) \bar\Lambda_2$, and $\langle\bar q q\rangle^{1/3}_{n_f=3}(2\, {\rm GeV}) = -(0.814-0.838) \bar\Lambda_3$, where the range is our estimated theoretical error and $\bar\Lambda_{n_f}$ the basic QCD scale in the $\overline{MS}$-scheme.
We update our previous analysis up to 5-loop order of (RG optimized) perturbation, thanks to the recently available five-loop order QCD renormalization group functions, and compare our results with other recent determinations from lattice simulations or other approaches.

### Primary authors

Jean-Loic Kneur (Univ. Montpellier) André Neveu (Lab. Charles Coulomb)