ScalingStacks

Proof. [03YS]

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Proof.

(Theorem 1.5, sketch) By formula (1.6) and the integrability condition (1.10),

(1.12) d​Fj=−12​(∂2Wp​q¯∂μi​∂μj+4​∂2Vi​j∂ηp​∂η¯q)​d​μi∧d​ηp∧d​η¯q,dF_{j}=\frac{\sqrt{-1}}{2}\left(\frac{\partial^{2}W^{p\bar{q}}}{\partial\mu_{i}\partial\mu_{j}}+4\frac{\partial^{2}V^{ij}}{\partial\eta_{p}\partial\bar{\eta}_{q}}\right)d\mu_{i}\wedge d\eta_{p}\wedge d\bar{\eta}_{q},

so the closedness of FjF_{j} is equivalent to (1.11). Since 12​π​F\frac{1}{2\pi}F represents the appropriate first Chern class, FF must be the curvature of a T𝔫T^{\mathfrak{n}}-connection ϑ\vartheta. Modulo gauge ϑ\vartheta admits the local formula

(1.13) ϑj=−1​{∂2Φ∂ηp​∂μ​d​ηp−∂2Φ∂η¯p​∂μ​d​η¯p}.\vartheta_{j}=\sqrt{-1}\{\frac{\partial^{2}\Phi}{\partial\eta_{p}\partial\mu}d\eta_{p}-\frac{\partial^{2}\Phi}{\partial\bar{\eta}_{p}\partial\mu}d\bar{\eta}_{p}\}.

Gauge equivalent choices of the connection define the structures on MM up to holomorphic isometry.

The integrability of the complex structure follows from the fact that the differential ideal generated by (1,0)(1,0) forms is closed:

(1.14) d​ζj=(12​∂Wp​q¯∂μj​d​η¯q−2​∂Vi​j∂ηp​d​μi)∧d​ηp,d\zeta_{j}=\left(\frac{1}{2}\frac{\partial W^{p\bar{q}}}{\partial\mu_{j}}d\bar{\eta}_{q}-2\frac{\partial V^{ij}}{\partial\eta_{p}}d\mu_{i}\right)\wedge d\eta_{p},

using (1.10)(1.6) and the definition of ζj\zeta_{j}. The Kähler condition d​ω=0d\omega=0 follows from (1.10)(1.6). The Calabi-Yau condition follows from the more general formula

ωN=det(Wp​q¯)​det(Vi​j)−1​N!2N​−1N2​Ω∧Ω¯.\omega^{N}=\det(W^{p\bar{q}})\det(V^{ij})^{-1}\frac{N!}{2^{N}}\sqrt{-1}^{N^{2}}\Omega\wedge\overline{\Omega}.

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