= Banks-Zaks fixed point
{c}
{title2=$a_*=-\beta_0/\beta_1$}
{wiki=Banks–Zaks_fixed_point}
A non-Abelian gauge theory can have a weak <infrared fixed point> when the one-loop coefficient of its <renormalization-group beta function> is small and positive while the two-loop coefficient is negative. For $a=g^2/(16\pi^2)$ and evolution in $\log\mu^2$, $\beta(a)=-\beta_0a^2-\beta_1a^3$ has the displayed zero and slope $-\beta_0^2/\beta_1>0$. Fundamental-fermion flavor number just below the asymptotic-freedom boundary produces this regime.
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