TheoremComplete

Homological Mirror Symmetry - Main Theorem

Kontsevich's homological mirror symmetry conjecture has been proven in several important cases, establishing categorical equivalences that underpin our understanding of mirror symmetry. These theorems provide rigorous foundations for the physical predictions.

TheoremHMS for Elliptic Curves (Polishchuk-Zaslow, 1998)

Let E=C/ΛE = \mathbb{C}/\Lambda be an elliptic curve and E^=C/Λ\hat{E} = \mathbb{C}/\Lambda^\vee its dual. There exists a triangulated equivalence: Db(Coh(E))DFuk(E^)D^b(Coh(E)) \simeq D\mathcal{F}uk(\hat{E})

The equivalence is constructed explicitly by:

  1. Sending line bundles Lα\mathcal{L}_\alpha to Lagrangian tori TαT_\alpha
  2. Sending skyscraper sheaves to Lagrangian circles
  3. Verifying Ext groups match Floer cohomology

This was the first rigorous proof of HMS and established the feasibility of the categorical approach.

The proof uses the fact that both sides can be described explicitly: coherent sheaves on EE are classified by degree and indecomposables, while Lagrangian submanifolds in E^\hat{E} are circles and tori.

TheoremHMS for Quartic K3 Surfaces (Seidel, 2003)

For a smooth quartic K3 surface SP3S \subset \mathbb{P}^3 and its mirror SS^\vee: Db(Coh(S))DFuk(S)D^b(Coh(S)) \simeq D\mathcal{F}uk(S^\vee)

The proof constructs the equivalence using:

  • Spherical objects and spherical twists
  • Lefschetz fibrations and vanishing cycles
  • Symplectic topology techniques

This extended HMS beyond tori to higher-dimensional Calabi-Yau manifolds.

TheoremOrlov's Theorem

Let XX and YY be smooth projective varieties. Every fully faithful exact functor: Φ:Db(Coh(X))Db(Coh(Y))\Phi: D^b(Coh(X)) \to D^b(Coh(Y))

is representable by a Fourier-Mukai kernel KDb(Coh(X×Y))\mathcal{K} \in D^b(Coh(X \times Y)): Φ(F)=RπY(πXFLK)\Phi(\mathcal{F}) = R\pi_{Y*}(\pi_X^*\mathcal{F} \otimes^L \mathcal{K})

This provides a framework for understanding derived equivalences algebraically.

Orlov's theorem implies that HMS equivalences on the B-side are always Fourier-Mukai. The challenge is constructing the corresponding Fukaya-Mukai kernels on the A-side.

TheoremHMS for Toric Varieties (Abouzaid-Auroux-Katzarkov)

For a smooth toric Fano variety XΣX_\Sigma and its Landau-Ginzburg mirror (M,W)(M, W): Db(Coh(XΣ))FS(M,W)D^b(Coh(X_\Sigma)) \simeq \mathcal{F}S(M, W)

where FS(M,W)\mathcal{F}S(M, W) is the Fukaya-Seidel category of the Landau-Ginzburg model.

Objects on the right are Lagrangian thimbles (vanishing cycles) associated to critical points of WW.

This theorem establishes HMS in the toric setting and connects to homological algebra of matrix factorizations, providing computational tools for both sides.

TheoremGeneration Criterion

The derived category Db(Coh(X))D^b(Coh(X)) for a smooth projective variety XX is generated as a triangulated category by any spanning class, i.e., a collection {Ei}\{\mathcal{E}_i\} such that: Hom(Ei,F[k])=0 for all i,k    F=0\text{Hom}(\mathcal{E}_i, \mathcal{F}[k]) = 0 \text{ for all } i, k \implies \mathcal{F} = 0

For HMS, proving the Fukaya category is generated by specific Lagrangians reduces the conjecture to verifying Ext/Floer isomorphisms for generators.

These theorems provide the mathematical foundation for homological mirror symmetry and demonstrate its feasibility across various geometric contexts.