Nonperturbative region of effective strong coupling

Understand

In the framework of Poincar\'{e} covariant quark model the behavior of running coupling constant $\alpha_{s}\left(Q^{2}\right)$ is considered in $Q < 1 \mbox{GeV}$ region.

• An analysis was carried out for pseudoscalar and vector mesons with lepton decay constants, masses (obtained from model dependent) and nucleon spin rules required to match their experimental counterparts.
• Possible behavior of $\alpha_{s}$ with $\alpha_{\mathrm{crit.}}=\alpha_{s}\left(Q^{2}=0\right) \sim 0.65-0.72$ in the case of a frozen regime, which follows from experimental values of lepton decay constant, masses and nucleon spin rules are discussed.