ScalingStacks

Proof. [051H]

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Proof.

We first consider ω~\tilde{\omega}. As z→±∞z\rightarrow\pm\infty the behavior of ω~\tilde{\omega} is governed by (3.349), so for T≫1T\gg 1 we know ω~\tilde{\omega} is positive over the region where z∈[−k−−1​(T−1),−k+−1​(T−1)]∖[−C,C]z\in[-k_{-}^{-1}(T-1),-k_{+}^{-1}(T-1)]\setminus[-C,C] for some number C>0C>0 independent of TT. By the expansion of ψ\psi in a neighborhood of PP given in Proposition 3.24, for TT sufficiently large, ω~\tilde{\omega} is also positive when z∈[−C,C]z\in[-C,C]. Hence ω~\tilde{\omega} is positive over the region where z∈[−k−−1​(T−1),−k+−1​(T−1)].z\in[-k_{-}^{-1}(T-1),-k_{+}^{-1}(T-1)]. Since this contains QTQ_{T} we see in particular ω~\tilde{\omega} is positive over QT∖PQ_{T}\setminus P.

To deal with hh we need to analyze q⁡(z)q(z). When |z|≥1|z|\geq 1, we have

(4.18) q⁡(z)=q0​(z)=T2−n​(T+k±​z)n−1−(n−1)​(T+k±​z),q(z)=q_{0}(z)=T^{2-n}(T+k_{\pm}z)^{n-1}-(n-1)(T+k_{\pm}z),

where the choice of ++ or −- depends on whether z>0z>0 or z<0z<0. By (3.349) we then get

(4.19) h=T2−n​(T+k±​z)n−1+ϵ⁡(z).h=T^{2-n}(T+k_{\pm}z)^{n-1}+\epsilon(z).

So we can find C>0C>0 such that hh is positive when z∈[T−,T+]∖[−C,C]z\in[T_{-},T_{+}]\setminus[-C,C]. On the other hand, on [−C,C][-C,C] we know by definition

(4.20) q⁡(z)=(2−n)​T+T−1​B​(z).q(z)=(2-n)T+T^{-1}B(z).

Hence by the expansion in Proposition 3.28 we obtain (4.17). This implies that for T≫1T\gg 1, hh is also positive when z∈[−C,C]z\in[-C,C]. ∎

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