Nonzero-wavevector soft-mode sphere
= Nonzero-wavevector soft-mode sphere
For $G(q)=a+\kappa q^2+\gamma q^4$ with $\kappa<0<\gamma$, the minimum occurs on the sphere $q=q_0=\sqrt{-\kappa/(2\gamma)}$. The minimum value is $a-\kappa^2/(4\gamma)$.
= Nonzero-wavevector soft-mode sphere
For $G(q)=a+\kappa q^2+\gamma q^4$ with $\kappa<0<\gamma$, the minimum occurs on the sphere $q=q_0=\sqrt{-\kappa/(2\gamma)}$. The minimum value is $a-\kappa^2/(4\gamma)$.