ScalingStacks

Theorem 4.5 [0322]

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Theorem 4.5

Let j:J→𝐏1j:J\rightarrow{\bf P}^{1} be an elliptically fibred K3 surface with section and 24 singular fibres over Δ={p1,…,p24}\Delta=\{p_{1},\ldots,p_{24}\} as above. Then there exists open sets U1i⊆U2i⊆𝐏1U_{1}^{i}\subseteq U_{2}^{i}\subseteq{\bf P}^{1}, i=1,…,24i=1,\ldots,24, each diffeomorphic to a disc, Uji∩Δ={pi}U^{i}_{j}\cap\Delta=\{p_{i}\}, positive constants D1,D2,D3,D4,D5D_{1},D_{2},D_{3},D_{4},D_{5} and ϵ0\epsilon_{0} such that, for all ϵ<ϵ0\epsilon<\epsilon_{0}, for any elliptic fibration f:X→𝐏1f:X\rightarrow{\bf P}^{1} with Jacobian j:J→𝐏1j:J\rightarrow{\bf P}^{1} with holomorphic 2-form Ω\Omega with [ReΩ]2=[ReΩJ]2[\mathop{\rm Re}\Omega]^{2}=[\mathop{\rm Re}\Omega_{J}]^{2}, and for any Kähler class [ωϵ][\omega_{\epsilon}] on XX with [ωϵ].Xb=ϵ[\omega_{\epsilon}].X_{b}=\epsilon and [ωϵ]2=[ReΩ]2=[ImΩ]2[\omega_{\epsilon}]^{2}=[\mathop{\rm Re}\Omega]^{2}=[\mathop{\rm Im}\Omega]^{2}, there exists a Kähler metric ωϵ\omega_{\epsilon} representing [ωϵ][\omega_{\epsilon}] on XX with the following properties:

(1) ωϵ|f−1​(𝐏1∖⋃iU2i)\omega_{\epsilon}|_{f^{-1}({\bf P}^{1}\setminus\bigcup_{i}U_{2}^{i})} is a semi-flat metric (not necessarily the standard one).

(2) ωϵ|f1​(U1i)=Tσi∗​ωO​V,\omega_{\epsilon}|_{f^{1}(U_{1}^{i})}=T_{\sigma_{i}}^{*}\omega_{OV}, where ωO​V\omega_{OV} is an Ooguri–Vafa metric and TσiT_{\sigma_{i}} denotes translation by a (not necessarily holomorphic) section.

(3) If Fϵ=log⁡(Ω∧Ω¯/2ωϵ2)F_{\epsilon}=\log\left({\Omega\wedge\bar{\Omega}/2\over\omega_{\epsilon}^{2}}\right), then

∥Fϵ∥C0≤D1e−D2/ϵ\|F_{\epsilon}\|_{C^{0}}\leq D_{1}e^{-D_{2}/\epsilon}

and

∥ΔFϵ∥C0≤D1e−D2/ϵ,\|\Delta F_{\epsilon}\|_{C^{0}}\leq D_{1}e^{-D_{2}/\epsilon},

where Δ\Delta denotes the Laplacian with respect to ωϵ\omega_{\epsilon}.

(4)

infv{Ric(v,v)||v|ωϵ=1}≥−D3e−D4/ϵ.inf_{v}\{Ric(v,v)\,|\ |v|_{\omega_{\epsilon}}=1\}\geq-D_{3}e^{-D_{4}/\epsilon}.

(5) With the Riemannian metric induced by ωϵ\omega_{\epsilon}, Diam(X)≤D5ϵ−1/2Diam(X)\leq D_{5}\epsilon^{-1/2}.

(6) If RR denotes the Riemann curvature tensor, then

‖R‖C0≤D6​ϵ−1​log⁡ϵ−1,\|R\|_{C^{0}}\leq D_{6}\epsilon^{-1}\log\epsilon^{-1},
‖R‖C0→∞\|R\|_{C^{0}}\rightarrow\infty as ϵ→0\epsilon\rightarrow 0,

and on any non-singular fibre, there exists a constant CC depending on the fibre such that

‖R‖≤C​ϵ.\|R\|\leq C\epsilon.

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