ScalingStacks

3.2.3. Completion of Proof [02BK]

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3.2.3. Completion of Proof

With this lengthy discussion involving the tangent cone in place, we return to the limit space X∞X_{\infty}. Recall that we have a sequence of scalings kν\sqrt{k_{\nu}}. We consider embeddings χν:U~→X∞reg\chi_{\nu}:\tilde{U}\rightarrow X^{{\rm reg}}_{\infty}. Given such a χν\chi_{\nu} we write JνJ^{\nu} for the pull-back of the complex structure on X∞regX_{\infty}^{{\rm reg}} and gνg^{\nu} for the pull-back of kνk_{\nu} times the metric.

Proposition 3.12.

There is a kνk_{\nu} so that we can find an embedding χν\chi_{\nu} as above, such that

  • •
    (1/2)kν−1/2|z|≤d(p,χν(z))≤2kν−1/2|z|;(1/2)k_{\nu}^{-1/2}|z|\leq d(p,\chi_{\nu}(z))\leq 2k_{\nu}^{-1/2}|z|;
  • •
    ‖Jν−J0‖U~,‖gν−g0‖U~≤ψ~/2.\|J^{\nu}-J_{0}\|_{\tilde{U}},\|g^{\nu}-g_{0}\|_{\tilde{U}}\leq\tilde{\psi}/2.

This follows easily from the general assertions in Section 2.1 about convergence. We now fix this kνk_{\nu} and define k⁡(p)=m​kνk(p)=mk_{\nu} and r(p)=ρk(p)−1/2r(p)=\rho k(p)^{-1/2}. We write χkν=χ\chi_{k_{\nu}}=\chi.

Let Xi∈𝒦⁡(n,C,V)X_{i}\in{\mathcal{K}}(n,C,V) be a sequence converging to X∞X_{\infty}. We fix distance functions on X∞⊔XiX_{\infty}\sqcup X_{i}. We consider embeddings χi:U~→Xi\chi^{i}:\tilde{U}\rightarrow X_{i}. Given such maps we write gi,Jig_{i},J_{i} for the pull backs of the metric and complex structure, Λi\Lambda_{i} for the pull-back of LkνL^{k_{\nu}} and AiA_{i} for the pulled back connection.

Proposition 3.13.

For large enough ii we can choose χi\chi^{i} with the following two properties.

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    d(χi(z),χ(z))≤ρk(p)−1/2/100d(\chi^{i}(z),\chi(z))\leq\rho k(p)^{-1/2}/100

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    ‖gi−g0‖U~,‖Ji−J0‖U~≤ψ~\|g_{i}-g_{0}\|_{\tilde{U}},\|J_{i}-J_{0}\|_{\tilde{U}}\leq\tilde{\psi}.

Again this follows from our general discussion of convergence.

Fix ii large enough, as in Proposition 3.13. We apply Proposition 3.11 to find a tt such that the pull-back by μt\mu_{t} of the data t​gi,Ji,Λit,Ai⊗ttg_{i},J_{i},\Lambda_{i}^{t},A^{\otimes t}_{i} has Property (H) over UU. Now write k=t​kνk=tk_{\nu} so k≤k⁡(p)k\leq k(p). We apply Proposition 2.4 to construct a holomorphic section ss of Lk→XiL^{k}\rightarrow X_{i}, with a fixed bound on the L2,♯L^{2,\sharp} norm and with |s⁡(x)|≥1/4|s(x)|\geq 1/4 at points xx with d♯​(x,χi​(u∗))<(4​K1)−1d^{\sharp}(x,\chi_{i}(u_{*}))<(4K_{1})^{-1}. Here we are writing d♯d^{\sharp} for the scaled metric, so in terms of the original metric the condition is d(x,χi(u∗))<k−1/2(4K1)−1d(x,\chi_{i}(u_{*}))<k^{-1/2}(4K_{1})^{-1}.

To finish, suppose q∈Xiq\in X_{i} has d⁡(q,p)≤r⁡(p)d(q,p)\leq r(p). By construction r(p)≤ρk−1/2r(p)\leq\rho k^{-1/2}. Note also that if we set p′=χi(t−1/2zρ)p^{\prime}=\chi^{i}(t^{-1/2}z_{\rho}). then

d(q,p′)≤d(q,p)+d(p,χ(t−1/2zρ))+d(χ(t−1/2zρ),χ(i)(t−1/2zρ))≤4ρk.d(q,p^{\prime})\leq d(q,p)+d(p,\chi(t^{-1/2}z_{\rho}))+d(\chi(t^{-1/2}z_{\rho}),\chi^{(i)}(t^{-1/2}z_{\rho}))\leq 4\rho\sqrt{k}.

This means that d♯​(q,p′)≤4​ρd^{\sharp}(q,p^{\prime})\leq 4\rho which is less than (4​K1)−1(4K_{1})^{-1} by our choice of ρ\rho.

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