Is the Number of Light Flavors in QCD Great?

摘要

At a qualitative level, it is well known that QCD featuring a large number of quark flavors must differ drastically from actual QCD. However, it is possible to consider the large-N_f limit (where N_f is the number of light flavors in QCD) such that the basic dynamics of the system remains unchanged. This is the region of chiral perturbation theory, where the limit N_f → ∞ is simultaneously the limit of a large number of colors, Nc. Features are indicated that make it possible, in such a situation, to compare analytically the same quantity in a simplified model of actual QCD and in the large-Nf limit, and methods are proposed for calculating these features. Calculations in the limit N_f → ∞ are of no use in assessing quantities of the theory at small N_f.