### Abstract

Motivated by the Petrie conjecture, we consider the following questions: Let a circle act in a Hamiltonian fashion on a compact symplectic manifold (M,ω) which satisfies H^{2i}(M;ℝ) = H ^{2i}(ℂℙ^{n},ℝ) for all i. Is Hj (M; ℤ) = H^{j} (ℂℙ^{n}; ℤ) for all j? Is the total Chern class of M determined by the cohomology ring H*(M; ℤ)? We answer these questions in the sixdimensional case by showing that H^{j} (M; ℤ) is equal to H^{j} (ℂℙ^{3}; ℤ) for all j, by proving that only four cohomology rings can arise, and by computing the total Chern class in each case. We also prove that there are no exotic actions. More precisely, if H*(M; ℤ) is isomorphic to H *(ℂℙ^{3}; ℤ) or H* (G̃_{2}(ℝ^{5}); ℤ), then the representations at the fixed components are compatible with one of the standard actions; in the remaining two cases, the representation is strictly determined by the cohomology ring. Finally, our results suggest a natural question: Do the remaining two cohomology rings actually arise? This question is closely related to some interesting problems in symplectic topology, such as embeddings of ellipsoids.

Original language | English (US) |
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Pages (from-to) | 3963-3996 |

Number of pages | 34 |

Journal | Transactions of the American Mathematical Society |

Volume | 362 |

Issue number | 8 |

DOIs | |

State | Published - Aug 1 2010 |

### ASJC Scopus subject areas

- Mathematics(all)
- Applied Mathematics