Lemma 2.10 (00PU) · ScalingStacks

00PU

Lemma 2.10. (cf. [15, Lemma 2.4 and Remark 2.5]) Let $f:[t_{0},\infty)\to[0,\infty)$ be a nonincreasing right-continuous function, such that

\begin{cases}f(t_{0})<\frac{1}{2B},\\ tf(\tau+t)\leq Bf(\tau)^{2},\quad\forall\tau\geq 0,\quad 0\leq t\leq 1,\\ \lim_{t\to\infty}f(t)=0.\end{cases}

Then $f(t)=0$ for $t\geq t_{0}+4Bf(t_{0})$ .

00PV

Proof. (Thm 2.7) Combining the first two ingredients, the function $f(t)=(\frac{\int_{\phi\leq-t}\omega_{\phi}^{n}}{\text{Vol}(X)})^{1/2n}$ satisfies

tf(t+\tau)\leq Bf(\tau)^{2},\quad 0\leq t\leq 1,\quad\tau\geq 0,

We conclude that for $t>t_{0}+4Bf(t_{0})$ the sublevel set $\{\phi\leq-t\}$ has zero $\omega_{\phi}$ -measure, and therefore zero capacity by Lemma 2.8, so $\phi$ has the lower estimate as claimed in the first statement.

For the second statement, by (2) we have an a priori exponential decay

f(t)\leq A^{1/2n}e^{-\alpha t/2n},\quad t\geq 0,

which allows us to find an appropriate $t_{0}$ . ∎