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In this paper, we collect a number of facts about double Hurwitz numbers, where the simple branch points are replaced by their more general analogues --- completed (r+1)-cycles. In particular, we give a geometric interpretation of these…

Combinatorics · Mathematics 2014-02-26 S. Shadrin , L. Spitz , D. Zvonkine

Double Hurwitz numbers count covers of the projective line by genus g curves with assigned ramification profiles over 0 and infinity, and simple ramification over a fixed branch divisor. Goulden, Jackson and Vakil have shown double Hurwitz…

Algebraic Geometry · Mathematics 2010-03-10 Renzo Cavalieri , Paul Johnson , Hannah Markwig

Hurwitz numbers count branched covers of the Riemann sphere with specified ramification, or equivalently, transitive permutation factorizations in the symmetric group with specified cycle types. Monotone Hurwitz numbers count a restricted…

Combinatorics · Mathematics 2012-10-15 I. P. Goulden , Mathieu Guay-Paquet , Jonathan Novak

We derive a closed-form expression for all genus 1 Hurwitz numbers, and give a simple new graph-theoretic interpretation of Hurwitz numbers in genus 0 and 1. (Hurwitz numbers essentially count irreducible genus g covers of the sphere, with…

Combinatorics · Mathematics 2007-05-23 Ravi Vakil

We define the double Gromov-Witten invariants of Hirzebruch surfaces in analogy with double Hurwitz numbers, and we prove that they satisfy a piecewise polynomiality property analogous to their 1-dimensional counterpart. Furthermore we show…

Algebraic Geometry · Mathematics 2015-12-02 Federico Ardila , Erwan Brugalle

Hurwitz numbers enumerate ramified coverings of the Riemann sphere with fixed ramification data. Certain kinds of ramification data are of particular interest, such as double Hurwitz numbers, which count covers with fixed arbitrary…

Combinatorics · Mathematics 2018-10-09 Marvin Anas Hahn

Double Hurwitz numbers enumerating weighted $n$-sheeted branched coverings of the Riemann sphere or, equivalently, weighted paths in the Cayley graph of $S_n$ generated by transpositions are determined by an associated weight generating…

Mathematical Physics · Physics 2018-06-26 Mathieu Guay-Paquet , J. Harnad

Hurwitz numbers count ramified genus $g$, degree $d$ coverings of the projective line with with fixed branch locus and fixed ramification data. Double Hurwitz numbers count such covers, where we fix two special profiles over $0$ and…

Combinatorics · Mathematics 2018-07-11 Marvin Anas Hahn

Hurwitz numbers count genus $g$, degree $d$ covers of the complex projective line with fixed branched locus and fixed ramification data. An equivalent description is given by factorisations in the symmetric group. Simple double Hurwitz…

Combinatorics · Mathematics 2019-04-05 Marvin Anas Hahn

Double Hurwitz numbers have at least four equivalent definitions. Most naturally, they count covers of the Riemann sphere by genus g curves with certain specified ramification data. This is classically equivalent to counting certain…

Algebraic Geometry · Mathematics 2013-03-08 Paul Johnson

Weighted Hurwitz numbers arise as coefficients in the power sum expansion of deformed hypergeometric $\tau$--functions. They specialise to essentially all known cases of Hurwitz numbers, including classical, monotone, strictly monotone and…

Combinatorics · Mathematics 2025-11-04 Marvin Anas Hahn , Brian O'Callaghan , Jonas Wahl

We study "pure-cycle" Hurwitz spaces, parametrizing covers of the projective line having only one ramified point over each branch point. We start with the case of genus-0 covers, using a combination of limit linear series theory and group…

Algebraic Geometry · Mathematics 2007-05-23 Fu Liu , Brian Osserman

Hurwitz numbers enumerate branched morphisms between Riemann surfaces. For a fixed elliptic target, Hurwitz numbers are intimately related to mirror symmetry following work of Dijkgraaf. In recent work of Chapuy and Dolega a new variant of…

Combinatorics · Mathematics 2024-10-28 Marvin Anas Hahn , Hannah Markwig

We give formulae for the cumulants of complex Wishart (LUE) and inverse Wishart matrices (inverse LUE). Their large-$N$ expansions are generating functions of double (strictly and weakly) monotone Hurwitz numbers which count constrained…

Mathematical Physics · Physics 2021-04-12 Fabio Deelan Cunden , Antoine Dahlqvist , Neil O'Connell

The Hurwitz form of a projective variety characterizes linear spaces of complementary dimension which meet the variety non-transversally. We extend this notion to varieties in a product of projective spaces. This parallels the multigraded…

Algebraic Geometry · Mathematics 2026-02-24 Elizabeth Pratt , Luca Sodomaco , Bernd Sturmfels

In this paper, we define tropical analogues of real Hurwitz numbers, i.e. numbers of covers of surfaces with compatible involutions satisfying prescribed ramification properties. We prove a correspondence theorem stating the equality of the…

Algebraic Geometry · Mathematics 2015-08-26 Hannah Markwig , Johannes Rau

We define the tropical moduli space of covers of a tropical line in the plane as weighted abstract polyhedral complex, and the tropical branch map recording the images of the simple ramifications. Our main result is the invariance of the…

Algebraic Geometry · Mathematics 2013-10-29 Arne Buchholz , Hannah Markwig

This article introduces mixed double Hurwitz numbers, which interpolate combinatorially between the classical double Hurwitz numbers studied by Okounkov and the monotone double Hurwitz numbers introduced recently by Goulden, Guay-Paquet and…

Combinatorics · Mathematics 2016-04-21 I. P. Goulden , Mathieu Guay-Paquet , Jonathan Novak

We give a bijective proof of Hurwitz formula for the number of simple branched coverings of the sphere by itself. Our approach extends to double Hurwitz numbers and yields new properties for them. In particular we prove for double Hurwitz…

Combinatorics · Mathematics 2014-10-27 Enrica Duchi , Dominique Poulalhon , Gilles Schaeffer

In this paper we revisit several recent results on monotone and strictly monotone Hurwitz numbers, providing new proofs. In particular, we use various versions of these numbers to discuss methods of derivation of quantum spectral curves…

Mathematical Physics · Physics 2017-08-22 A. Alexandrov , D. Lewanski , S. Shadrin