Speaker
Description
There is a flavor number range of $SU(3)$ gauge theory, $N_f^* < N_f < 16.5$, where spontaneous chiral symmetry breaking does not occur and the model is conformal. The upper end $16.5$ is determined by the 1-loop $\beta$-function but the lower end $N_f^*$ may be determined by non-perturbative phenomena. In this contribution a new approach is presented to estimate or constrain $N_f^*$: high order perturbative results are presented for meson masses and decay constants valid close to the upper end, $N_f \simeq 16.5$, and these are matched to continuum extrapolated lattice results in the range $2 \leq N_f \leq 10$. An attempt is made to match them in the intermediate range. It appears a significant qualitative change occurs in the studied quantities at around $N_f = 12$.
