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Monotone Hurwitz Numbers in Genus Zero

  Published:2012-10-30
 Printed: Oct 2013
  • I. P. Goulden,
    Department of Combinatorics and Optimization, University of Waterloo, Canada
  • Mathieu Guay-Paquet,
    Department of Combinatorics and Optimization, University of Waterloo, Canada
  • Jonathan Novak,
    Department of Mathematics, Massachusetts Institute of Technology, USA
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Abstract

Hurwitz numbers count branched covers of the Riemann sphere with specified ramification data, or equivalently, transitive permutation factorizations in the symmetric group with specified cycle types. Monotone Hurwitz numbers count a restricted subset of these branched covers related to the expansion of complete symmetric functions in the Jucys-Murphy elements, and have arisen in recent work on the the asymptotic expansion of the Harish-Chandra-Itzykson-Zuber integral. In this paper we begin a detailed study of monotone Hurwitz numbers. We prove two results that are reminiscent of those for classical Hurwitz numbers. The first is the monotone join-cut equation, a partial differential equation with initial conditions that characterizes the generating function for monotone Hurwitz numbers in arbitrary genus. The second is our main result, in which we give an explicit formula for monotone Hurwitz numbers in genus zero.
Keywords: Hurwitz numbers, matrix models, enumerative geometry Hurwitz numbers, matrix models, enumerative geometry
MSC Classifications: 05A15, 14E20, 15B52 show english descriptions Exact enumeration problems, generating functions [See also 33Cxx, 33Dxx]
Coverings [See also 14H30]
Random matrices
05A15 - Exact enumeration problems, generating functions [See also 33Cxx, 33Dxx]
14E20 - Coverings [See also 14H30]
15B52 - Random matrices
 

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