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Volume 75, Nº 6 (2020)

Ano: 2020
Artigos: 10
URL: https://journals.rcsi.science/0042-1316/issue/view/7519

Iterated Laurent series over rings and the Contou-Carrère symbol

Gorchinskiy S., Osipov D.

Resumo

This article contains a survey of a new algebro-geometric approach for working with iterated algebraic loop groups associated with iterated Laurent series over arbitrary commutative rings and its applications to the study of the higher-dimensional Contou-Carrère symbol. In addition to the survey, the article also contains new results related to this symbol.The higher-dimensional Contou-Carrère symbol arises naturally when one considers deformation of a flag of algebraic subvarieties of an algebraic variety. The non-triviality of the problem is due to the fact that, in the case $n>1$, for the group of invertible elements of the algebra of $n$-iterated Laurent series over a ring, no representation is known in the form of an ind-flat scheme over this ring. Therefore, essentially new algebro-geometric constructions, notions, and methods are required. As an application of the new methods used, a description of continuous homomorphisms between algebras of iterated Laurent series over a ring is given, and an invertibility criterion for such endomorphisms is found. It is shown that the higher-dimensional Contou-Carrère symbol, restricted to algebras over the field of rational numbers, is given by a natural explicit formula, and this symbol extends uniquely to all rings. An explicit formula is also given for the higher-dimensional Contou-Carrère symbol in the case of all rings. The connection with higher-dimensional class field theory is described.As a new result, it is shown that the higher-dimensional Contou-Carrère symbol has a universal property. Namely, if one fixes a torsion-free ring and considers a flat group scheme over this ring such that any two points of the scheme are contained in an affine open subset, then after restricting to algebras over the fixed ring, all morphisms from the $n$-iterated algebraic loop group of the Milnor $K$-group of degree $n+1$ to the above group scheme factor through the higher-dimensional Contou-Carrère symbol.Bibliography: 67 titles.

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Uspekhi Matematicheskikh Nauk. 2020;75(6):3-84

3-84

(Rus)

(JATS XML)

Quasi-classical approximation for magnetic monopoles

Kordyukov Y., Taimanov I.

Resumo

A quasi-classical approximation is constructed to describe the eigenvalues of the magnetic Laplacian on a compact Riemannian manifold in the case when the magnetic field is given by a non-exact 2-form. For this, the multidimensional WKB method in the form of the Maslov canonical operator is applied. In this case, the canonical operator takes values in sections of a non-trivial line bundle. The constructed approximation is demonstrated for the example of the Dirac magnetic monopole on the two-dimensional sphere.Bibliography: 18 titles.

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Uspekhi Matematicheskikh Nauk. 2020;75(6):85-106

85-106

(Rus)

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The Dickman–Goncharov distribution

Molchanov S., Panov V.

Resumo

In the 1930s and 40s, one and the same delay differential equation appeared in papers by two mathematicians, Karl Dickman and Vasily Leonidovich Goncharov, who dealt with completely different problems. Dickman investigated the limit value of the number of natural numbers free of large prime factors, while Goncharov examined the asymptotics of the maximum cycle length in decompositions of random permutations. The equation obtained in these papers defines, under a certain initial condition, the density of a probability distribution now called the Dickman–Goncharov distribution (this term was first proposed by Vershik in 1986). Recently, a number of completely new applications of the Dickman–Goncharov distribution have appeared in mathematics (random walks on solvable groups, random graph theory, and so on) and also in biology (models of growth and evolution of unicellular populations), finance (theory of extreme phenomena in finance and insurance), physics (the model of random energy levels), and other fields. Despite the extensive scope of applications of this distribution and of more general but related models, all the mathematical aspects of this topic (for example, infinite divisibility and absolute continuity) are little known even to specialists in limit theorems. The present survey is intended to fill this gap. Both known and new results are given.Bibliography: 62 titles.

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Uspekhi Matematicheskikh Nauk. 2020;75(6):107-152

107-152

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Spinning tops and magnetic orbits

Novikov S.

Resumo

A number of directions were initiated by the author and his students in their papers of 1981–1982. However, one of them, concerning the properties of closed orbits on the sphere $S^2$ and in the groups $S^3$ and $\operatorname{SO}_3$, has not been sufficiently developed. This paper revives the discussion of these questions, states unsolved problems, and explains what was regarded as fallacies in old papers. In general, magnetic orbits have been poorly discussed in the literature on dynamical systems and theoretical mechanics, but Grinevich has pointed out that in theoretical physics one encounters similar situations in the theory related to particle accelerators such as proton cyclotrons. It is interesting to look at Chap. III of Landau and Lifshitz's Theoretical physics, vol. 2, Field theory (translated into English as The classical theory of fields [12]), where mathematical relatives of our situations occur, but the physics is completely different and there are actual strong magnetic fields.Bibliography: 12 titles.

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Uspekhi Matematicheskikh Nauk. 2020;75(6):153-161

153-161