The Sullivan Conjecture for smooth complete intersections

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A complete intersection Xn(d‾)⊆CPn+kX_n(\underline d)\subseteq\mathbb{C}P^{n+k} is the transverse intersection of kk complex hypersurfaces of multidegree d‾=(d1,…,dk)\underline d=(d_1,\ldots,d_k). Let d=d1⋯dkd=d_1\cdots d_k be its total degree. Its Sullivan data is

SDn(d‾):=(d,(pi(n,d‾))i=1⌊n/2⌋,χ(Xn(d‾))),SD_n(\underline d):=\bigl(d,(p_i(n,\underline d))_{i=1}^{\lfloor n/2\rfloor},\chi(X_n(\underline d))\bigr),

where pi(n,d‾)p_i(n,\underline d) are defined by pi(Xn(d‾))=pi(n,d‾)x2ip_i(X_n(\underline d))=p_i(n,\underline d)x^{2i} and x∈H2(Xn(d‾))x\in H^2(X_n(\underline d)) is the pullback of a generator of H2(CPn+k)H^2(\mathbb{C}P^{n+k}). The Sullivan Conjecture. Suppose that Xn(d‾)X_n(\underline d) and Xn(d‾′)X_n(\underline d') are complete intersections with SDn(d‾)=SDn(d‾′)SD_n(\underline d)=SD_n(\underline d'). If n≥3n\geq 3, then Xn(d‾)X_n(\underline d) is diffeomorphic to Xn(d‾′)X_n(\underline d'). This conjecture organises the smooth classification of complete intersections; prior results established it under divisibility hypotheses and up to the action of the group of homotopy 88-spheres, while the paper studies the remaining diffeomorphism and inertia-group issues in dimension 44.

References

Primary source

Diarmuid Crowley and Csaba Nagy, “The smooth classification of 4-dimensional complete intersections”, arXiv:2003.09216 (2025).

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