Lower bounds for the degree of a branched covering of a manifold
type: Item
instance of: scholarly article
title: Lower bounds for the degree of a branched covering of a manifold
zbMATH Open document ID: 1402.57004
DOI: 10.1134/S0001434618010200
author: D. V. Gugnin
published in: Mathematical Notes
publication date: 2018-06-25T00:00:00Z
review text: This paper is about lower bounds for the number of sheets of a branched covering between two manifolds \(X\to Y\) of the same dimension. The main result is given in terms of the cohomology rings of the spaces involved. More precisely the author considers the following question: Suppose given two manifolds \(X^N\) and \(Y^N\) for which at least one branched covering \(f:X^N\to Y^N\) exists. What is a lower bound for the least degree \(n\) of such a branched covering in terms of the topology of these manifolds? The main result of the manuscript is: Theorem 3: Let \(k\geq 1\) and \(N\geq 4k+2\) be any fixed integers. Given a connected closed orientable \(N\)-manifold \(X^N\) with \(L(X)=N\), let \[ Y^N:=S^2\times \cdots \times S^2\times S^{N-2k}. \] Then any \(n\)-fold branched covering \(f: X^N \to Y^{N-2k}\) satisfies the condition \(n\geq N-2k.\) Here \(L(X)\) is the rational cohomological length of the space \(X\). This improves substantially the best known general result for a lower bound for the integer \(n\). The main ingredient to prove the result is Lemma \(1\), which compares the ring structure of a ring obtained as the fixed subring of an action of a group \(G\) over a graded commutative algebra, with the ring obtained as the fixed subring of the restricted action to a subgroup \(H\subset G\) of finite index.
reviewed by: Daciberg Lima Gonçalves
Mathematics Subject Classification ID: 57M12
Mathematics Subject Classification ID: 55M35
Mathematics Subject Classification ID: 20J06
zbMATH DE Number: 6893884
zbMATH Keywords: branched covering
zbMATH Keywords: degree
zbMATH Keywords: cohomological lenght
zbMATH Keywords: symmetric power space
MaRDI profile type: Publication
cites work: Q5337813
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description: scientific article; zbMATH DE number 6893884