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**Local orders, root numbers, and modular curves.**
*(English)*
Zbl 0675.12011

Let F be a local field. Let \(\pi\) be an irreducible admissible representation of \(GL(2,F)\) and \(\pi_{\chi}\) the representation of \(GL(2,F)\) which corresponds (via the Weil representation) to a character \(\chi\) of a quadratic extension of F. Assume the restriction of \(\chi^{-1}\) to \(F^*\) is equal to the central character of \(\pi\). Then \(\pi \times \pi_{\chi}\) is isomorphic to its dual and its L-function gives us a root number \(\pm 1.\) Using the determination of this root number the author associates to \(\pi\) and \(\chi\) a quaternion algebra B over F and an irreducible representation E of \(B^*\), which is either \(\pi\) or the representation corresponding to it according to Jacquet- Langlands in the case when B is the division algebra. When \(\pi\) and \(\pi_{\chi}\) have little common ramification a certain order R in B is defined such that E contains (up to a scalar) a unique vector invariant under \(R^*\). This is a generalization of the theory of new vectors.

This local result is applied in the global situation to a certain eigenspace of the Hecke algebra. Here the two different cases are considered: the local algebras \(B_ v\) may come from a global quaternion algebra or not.

This local result is applied in the global situation to a certain eigenspace of the Hecke algebra. Here the two different cases are considered: the local algebras \(B_ v\) may come from a global quaternion algebra or not.

Reviewer: J.G.M.Mars

### MSC:

11S45 | Algebras and orders, and their zeta functions |

11F70 | Representation-theoretic methods; automorphic representations over local and global fields |

11S40 | Zeta functions and \(L\)-functions |

11S37 | Langlands-Weil conjectures, nonabelian class field theory |

20G25 | Linear algebraic groups over local fields and their integers |

14H25 | Arithmetic ground fields for curves |