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The main goal of the present paper are new formulae for degrees of strata in Hurwitz spaces of rational functions having two degenerate critical values with preimages of prescribed multiplicities. We consider the case where the…

Algebraic Geometry · Mathematics 2016-11-03 Boris Bychkov

The construction of hypergeometric $2D$ Toda $\tau$-functions as generating functions for weighted Hurwitz numbers is extended to multispecies families. Both the enumerative geometrical significance of multispecies weighted Hurwitz numbers,…

Mathematical Physics · Physics 2018-06-26 J. Harnad

We explain how Gaussian integrals over ensemble of complex matrices with source matrices generate Hurwitz numbers of the most general type, namely, Hurwitz numbers with arbitrary orientable or non-orientable base surface and arbitrary…

Mathematical Physics · Physics 2020-03-10 Sergei M. Natanzon , Aleksandr Yu. Orlov

There is a way of assigning a realizability notion to each degree of incomputability. In our setting, we make use of Weihrauch degrees (degrees of incomputability/discontinuity of partial multi-valued functions) to obtain Lifschitz-like…

Logic · Mathematics 2025-05-07 Takayuki Kihara

We interpret the degrees which arise in Tevelev's study of scattering amplitudes in terms of moduli spaces of Hurwitz covers. Via excess intersection theory, the boundary geometry of the Hurwitz moduli space yields a simple recursion for…

Algebraic Geometry · Mathematics 2023-07-19 Alessio Cela , Rahul Pandharipande , Johannes Schmitt

We review and explain an infinite-dimensional counterpart of the Hurwitz theory realization of algebraic open-closed string model a la Moore and Lizaroiu, where the closed and open sectors are represented by conjugation classes of…

High Energy Physics - Theory · Physics 2013-03-07 A. Mironov , A. Morozov , S. Natanzon

Hurwitz spaces are moduli of isotopy classes of covers. A specific space is formed from a finite group G and C, r of its conjugacy classes and an equivalence relation \dagger. Components, interpret as a braid orbits on Nielsen classes.…

Algebraic Geometry · Mathematics 2025-09-12 Michael D. Fried

We define the dimension 2g-1 Faber-Hurwitz Chow/homology classes on the moduli space of curves, parametrizing curves expressible as branched covers of P^1 with given ramification over infinity and sufficiently many fixed ramification points…

Algebraic Geometry · Mathematics 2007-05-23 Ian P. Goulden , David M. Jackson , Ravi Vakil

In this paper, the generic intersection theory for difference varieties is presented. Precisely, the intersection of an irreducible difference variety of dimension $d > 0$ and order $h$ with a generic difference hypersurface of order $s$ is…

Algebraic Geometry · Mathematics 2013-08-27 Wei Li , Ying-Hong Li

In this paper we examine different problems regarding complete intersection varieties of high degree in a complex projective space. First we show how one can deduce hyperbolicity for generic complete intersection of high multidegree and…

Algebraic Geometry · Mathematics 2019-02-20 Damian Brotbek

We study intersections of projective convex sets in the sense of Steinitz. In a projective space, an intersection of a nonempty family of convex sets splits into multiple connected components each of which is a convex set. Hence, such an…

Metric Geometry · Mathematics 2010-05-12 Takahisa Toda

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

Hurwitz spaces which parametrize branched covers of the line play a prominent role in inverse Galois theory. This paper surveys fifty years of works in this direction with emphasis on recent advances. Based on the Riemann-Hurwitz theory of…

Number Theory · Mathematics 2026-04-14 Pierre Dèbes

We consider the problem of constructing triangulations of projective planes over Hurwitz algebras with minimal numbers of vertices. We observe that the numbers of faces of each dimension must be equal to the dimensions of certain…

Algebraic Geometry · Mathematics 2013-11-14 Frédéric Chapoton , Laurent Manivel

We introduce invariants of Hurwitz equivalence classes with respect to arbitrary group $G$. The invariants are constructed from any right $G$-modules $M$ and any $G$-invariant bilinear function on $M$, and are of bilinear forms. For…

Geometric Topology · Mathematics 2017-02-02 Takefumi Nosaka

Hurwitz numbers count genus g, degree d covers of the projective line with fixed branch locus. This equals the degree of a natural branch map defined on the Hurwitz space. In tropical geometry, algebraic curves are replaced by certain…

Algebraic Geometry · Mathematics 2010-07-19 Renzo Cavalieri , Paul Johnson , Hannah Markwig

The degree of a projective subscheme has an upper bound in term of the codimension and the reduction number. If a projective variety has an almost maximal degree, that is, the degree equals to the upper bound minus one, then its Betti table…

Commutative Algebra · Mathematics 2021-01-19 Doan Trung Cuong , Sijong Kwak

The Hurwitz space is a compactification of the space of rational functions of a given degree. We study the intersection of various strata of this space with its boundary. A study of the cohomology ring of the Hurwitz space then allows us to…

Algebraic Geometry · Mathematics 2007-05-23 Dimitri Zvonkine

We generalise Birch's seminal work on forms in many variables to handle a system of forms in which the degrees need not all be the same. This allows us to prove the Hasse principle, weak approximation, and the Manin-Peyre conjecture for a…

Number Theory · Mathematics 2015-02-03 T. D. Browning , D. R. Heath-Brown

Several generalizations of a commutative ring that is a graded complete intersection are proposed for a noncommutative graded $k$-algebra; these notions are justified by examples from noncommutative invariant theory.

Rings and Algebras · Mathematics 2014-06-25 Ellen E Kirkman , James Kuzmanovich , James J. Zhang