geometry-topology / Symplectic topology; exact Lagrangians in cotangent bundles

Arnold's nearby Lagrangian conjecture

Theorem 1.1: for some sufficiently large even NN, Q=S9×SN−1Q=S^9\times S^{N-1} admits a closed exact smoothly embedded Lagrangian L⊂T∗QL\subset T^*Q, diffeomorphic to QQ and with QQ and LL simply connected, that no compactly supported Hamiltonian isotopy carries to the zero section. LL is cut out by a generating family whose data at infinity form a nontrivial class a∈π9a\in\pi_9 of the stable smooth tube space with trivial associated spherical fibration; a Morse and h-cobordism argument shows such data cannot come from a family with one nondegenerate critical point per fibre, as an isotopy to the zero section would force. Not shown: an explicit NN, counterexamples in low dimension, or any failure of the homotopy-theoretic consequences already proved.

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geometry-topologySep 23, 2026Significance 62/100Registry: unreviewed

Arnold's nearby Lagrangian conjecture

Prior state unknown→disproved

Theorem 1.1: for some sufficiently large even NN, Q=S9×SN−1Q=S^9\times S^{N-1} admits a closed exact smoothly embedded Lagrangian L⊂T∗QL\subset T^*Q, diffeomorphic to QQ and with QQ and LL simply connected, that no compactly supported Hamiltonian isotopy carries to the zero section. LL is cut out by a generating family whose data at infinity form a nontrivial class a∈π9a\in\pi_9 of the stable smooth tube space with trivial…

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Theorem 1.1: for some sufficiently large even NN, Q=S9×SN−1Q=S^9\times S^{N-1} admits a closed exact smoothly embedded Lagrangian L⊂T∗QL\subset T^*Q, diffeomorphic to QQ and with QQ and LL simply connected, that no compactly supported Hamiltonian isotopy carries to the zero section. LL is cut out by a generating family whose data at infinity form a nontrivial class a∈π9a\in\pi_9 of the stable smooth tube space with trivial associated spherical fibration; a Morse and h-cobordism argument shows such data cannot come from a family with one nondegenerate critical point per fibre, as an isotopy to the zero section would force. Not shown: an explicit NN, counterexamples in low dimension, or any failure of the homotopy-theoretic consequences already proved.

Theorem 1.1: for some sufficiently large even NN, Q=S9×SN−1Q=S^9\times S^{N-1} admits a closed exact smoothly embedded Lagrangian L⊂T∗QL\subset T^*Q, diffeomorphic to QQ and with QQ and LL simply connected, that no compactly supported Hamiltonian isotopy carries to the zero section. LL is cut out by a generating family whose data at infinity form a nontrivial class a∈π9a\in\pi_9 of the stable smooth tube space with trivial associated spherical fibration; a Morse and h-cobordism argument shows such data cannot come from a family with one nondegenerate critical point per fibre, as an isotopy to the zero section would force. Not shown: an explicit NN, counterexamples in low dimension, or any failure of the homotopy-theoretic consequences already proved.

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