Cyclotomy and endomotives

We compare two different models of noncommutative geometry of the cyclotomic tower, both based on an arithmetic algebra of functions of roots of unity and an action by endomorphisms, the first based on the Bost-Connes (BC) quantum statistical mechanical system and the second on the Habiro ring, where the Habiro functions have, in addition to evaluations at roots of unity, also full Taylor expansions. Both have compatible endomorphisms actions of the multiplicative semigroup of positive integers. As a higher dimensional generalization, we consider a crossed product ring obtained using Manin’s multivariable generalizations of the Habiro functions and an action by endomorphisms of the semigroup of integer matrices with positive determinant. We then construct a corresponding class of multivariable BC endomotives, which are obtained geometrically from self maps of higher dimensional algebraic tori, and we discuss some of their quantum statistical mechanical properties. These multivariable BC endomotives are universal for (torsion free) Λ-rings, compatibly with the Frobenius action. Finally, we discuss briefly how Habiro’s universal Witten-Reshetikhin-Turaev invariant of integral homology 3-spheres may relate invariants of 3-manifolds to gadgets over and semigroup actions on homology 3-spheres to endomotives. The text was submitted by the author in English.     

Perfect addition sets

A subset S of Z_n is called a perfect addition set if the form x+y, for x≠ y in S, does not represent 0 and represents all non-zero elements the same number of times. The known perfect addition sets with 1?2 elements are (up to equivalence) one for each prime n=4a+3>3 and one each for n=2,4. It is shown that there are no others with 21>n?9, or with l divisible by 5; and there are some other restrictions.     

Polynomial addition sets and polynomial digraphs

Let G be a group of order v, and f(x) be a nonzero integral polynomial. A (v, k, f(x))-polynomial addition set in G is a subset D of G with k distinct elements such that f(Σ_d∈Dd) = λΣ_g∈Gg for some integer λ. We discuss some general properties of polynomial addition sets. The relation between polynomial addition sets and polynomial Cayley digraphs is studied and, in particular, some new results on Cayley xⁿ-digraphs and strongly regular Cayley graphs are obtained. Finally, a complete list of polynomial addition sets with certain restrictions on parameters is given.     

Cyclotomy and Strongly Regular Graphs

We consider strongly regular graphs defined on a finite field by taking the union of some cyclotomic classes as difference set. Several new examples are found.     

On multipliers of polynomial addition sets

Let G be a group of order v, and f(x) be a nonzero integral polynomial. A (v, k, f(x))-polynomial addition set in G is a subset D of G with k distinct elements such that f(Σ_d?Dd) = λΣ_g?Gg for some integer λ. We discuss the multipliers of polynomial addition sets. The structure of some polynomial addition sets is studied, and in particular, we give a complete characterization of the case where G is cyclic and f(x) is irreducible.     

On multipliers of partial addition sets

Let G be a finite group not necessarily abelian. We prove a multiplier theorem for a normal partial addition set in G (i.e. a partial addition set which is a union of conjugacy classes).The second author gratefully acknowledges the financial support by the CNR which made this work possible.     

The existence and nonexistence of perfect addition sets

A (v, k, λ, μ)-perfect addition set is a subset A of $\text{Z}\text{υZ}$ with k elements such that the expression a_i + a_j, for a_i ≠ a_j in A, represents 0 exactly μ times and each nonzero element exactly λ times. Several infinite classes of such sets using quadratic residues of primes, a few isolated examples using cubic residues, and a construction in certain cases when υ is twice an odd integer, are give. There is an efficient method, based on the Chinese remainder theorem, which decides the existence or nonexistence of a perfect addition set. Some further results on nonexistence are given. In particular, two previously unsolved cases of Isbell (Discrete Math. 24 (1978), 13–18) are settled. The article ends with a list of nontrivial perfect addition sets with k ? 20.     

Cyclotomy and permutation polynomials of large indices

We use cyclotomy to construct new classes of permutation polynomials over finite fields. This allows us to generate permutation polynomials in an algorithmic way and also to unify several previous constructions. Many permutation polynomials constructed in this way have large indices.     

Cyclotomy and its application to duadic codes

In this paper we treat cyclotomic binary duadic codes. The conjecture of Ding and Pless is that there are infinitely many cyclotomic duadic codes of prime lengths that are not quadratic residue codes. We shall prove this conjecture by using the special case of Tschebotareff's density theorem.     

Properties of efficient solution sets under addition of objectives

This paper addresses a general multicriteria optimization problem under various optimality principles. We investigate the behavior of the sets of Pareto and lexicographic optima when considering an additional objective.     

Decomposing the real line into Borel sets closed under addition

We consider decompositions of the real line into pairwise disjoint Borel pieces so that each piece is closed under addition. How many pieces can there be? We prove among others that the number of pieces is either at most 3 or uncountable, and we show that it is undecidable in and even in the theory if the number of pieces can be uncountable but less than the continuum. We also investigate various versions: what happens if we drop the Borelness requirement, if we replace addition by multiplication, if the pieces are subgroups, if we partition (0, ∞), and so on.     

On the addition of convex sets in the hyperbolic plane

Analogue to the definition $K + L := \bigcup_{x\in K}(x + L)$ of the Minkowski addition in the euclidean geometry it is proposed to define the (noncommutative) addition $K \vdash L := \bigcup_{0\, \leqsl\, \rho\,\leqsl\, a(\varphi),0\,\leqsl\,\varphi\,<\, 2\pi}T_{\rho}^{(\varphi)}(L)$ for compact, convex and smoothly bounded sets K and L in the hyperbolic plane $\Omega$ (Kleins model). Here $\rho = a(\varphi)$ is the representation of the boundary $\partial$ K in geodesic polar coordinates and $T_{\rho}^{(\varphi)}$ is the hyperbolic translation of $\Omega$ of length $\rho$ along the line through the origin o of direction $\varphi$. In general this addition does not preserve convexity but nevertheless we may prove as main results: (1) $o \in$ int $K, o \in$ int L and K,L horocyclic convex imply the strict convexity of $K \vdash L$, and (2) in this case there exists a hyperbolic mixed volume $V_h(K,L)$ of K and L which has a representation by a suitable integral over the unit circle.     

“割圆术”在高等数学教学设计中的体现

研究“割圆术”思想在高等数学教学中的教学设计,讨论基于“割圆术”思想在教学中设置疑问与思考的方法,并将“割圆术”作为重要极限的应用,推导出“割圆术”中的圆面积公式．     

Banach algebra technique for proving an addition formula for spectral multiplicities of sets of operators

We use a Banach algebra technique to compute the spectral multiplicity of some sets of commuting operators.     

Wiggly sets and limit sets

We show that a compact, connected set which has uniform oscillations at all points and at all scales has dimension strictly larger than 1. We also show that limit sets of certain Kleinian groups have this property. More generally, we show that ifG is a non-elementary, analytically finite Kleinian group, and its limit set Λ(G) is connected, then Λ(G) is either a circle or has dimension strictly bigger than 1. The first author is partially supported by NSF Grant DMS 95-00577 and an Alfred P. Sloan research fellowship. The second author is partially supported by NSF grant DMS-94-23746.     

Vandermonde sets and super-Vandermonde sets

Given a set TGF(q), |T|=t, w_T is defined as the smallest positive integer k for which ∑_yTy^k≠0. It can be shown that w_Tt always and w_Tt−1 if the characteristic p divides t. T is called a Vandermonde set if w_Tt−1 and a super-Vandermonde set if w_T=t. This (extremal) algebraic property is interesting for its own right, but the original motivation comes from finite geometries. In this paper we classify small and large super-Vandermonde sets.