## Abstract

We study double Hurwitz numbers in genus zero counting the number of covers ℂP ^{1} → ℂP ^{1} with two branching points with a given branching behavior. By the recent result due to Goulden, Jackson and Vakil, these numbers are piecewise polynomials in the multiplicities of the preimages of the branching points. We describe the partition of the parameter space into polynomiality domains, called chambers, and provide an expression for the difference of two such polynomials for two neighboring chambers. Besides, we provide an explicit formula for the polynomial in a certain chamber called totally negative, which enables us to calculate double Hurwitz numbers in any given chamber as the polynomial for the totally negative chamber plus the sum of the differences between the neighboring polynomials along a path connecting the totally negative chamber with the given one.

Original language | English |
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State | Published - 2007 |

Event | 19th International Conference on Formal Power Series and Algebraic Combinatorics, FPSAC'07 - Tianjin, China Duration: 2 Jul 2007 → 6 Jul 2007 |

### Conference

Conference | 19th International Conference on Formal Power Series and Algebraic Combinatorics, FPSAC'07 |
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Country/Territory | China |

City | Tianjin |

Period | 2/07/07 → 6/07/07 |

## Keywords

- Double Hurwits numbers
- Piecewise polynomiality

## ASJC Scopus subject areas

- Algebra and Number Theory