Elementary operators on antiliminal C^*-algebras

We establish the equivalence of the following three properties of a -algebra A. (a) Every positive elementary operator on A is completely positive. (b) The norm and the cb-norm coincide for every elementary operator on A. (c) A is an extension of an antiliminal -algebra by an abelian one. Received: 15 July 1998 / in revised form: 22 September 1998     

Hodge theory for elliptic complexes over unital C^*-algebras

For a unital $C^{*}$ -algebra $A$ , we prove that the cohomology groups of $A$ -elliptic complexes of pseudodifferential operators in finitely generated projective $A$ -Hilbert bundles over compact manifolds are finitely generated $A$ -modules and Banach spaces provided the images of certain extensions of the so-called associated Laplacians are closed. We also prove that under this condition, the cohomology groups are isomorphic to the kernels of the associated Laplacians. This establishes a Hodge theory for these structures.     

On K-theoretic invariants of semigroup C*-algebras attached to number fields

We show that semigroup C*-algebras attached to ax+b$ax+b$-semigroups over rings of integers determine number fields up to arithmetic equivalence, under the assumption that the number fields have the same number of roots of unity. For finite Galois extensions, this means that the semigroup C*-algebras are isomorphic if and only if the number fields are isomorphic.     

C*-algebras associated with interval maps

For each piecewise monotonic map of , we associate a pair of C*-algebras and and calculate their K-groups. The algebra is an AI-algebra. We characterize when and are simple. In those cases, has a unique trace, and is purely infinite with a unique KMS state. In the case that is Markov, these algebras include the Cuntz-Krieger algebras , and the associated AF-algebras . Other examples for which the K-groups are computed include tent maps, quadratic maps, multimodal maps, interval exchange maps, and -transformations. For the case of interval exchange maps and of -transformations, the C*-algebra coincides with the algebras defined by Putnam and Katayama-Matsumoto-Watatani, respectively.

     

Class numbers of algebraic number fields of Eisenstein type,II

Let K be an algebraic number field, of degree n, with a completely ramifying prime p, and let t be a common divisor of n and $\text{(p ? 1)}\text{2}$. Then it is proved that if K does not contain the unique subfield, of degree t, of the p-th cyclotomic number field, then we have (h_K, n) > 1, where h_K is the class number of K. As applications, we give several results on h_K of such algebraic number fields K.     

The polylogarithm in algebraic number fields

Based on Kummer's 2-variable functional equations for the second through fifth orders of the polylogarithm function, certain linear combinations, with rational coefficients, of polylogarithms of powers of an algebraic base were discovered to possess significant mathematical properties. These combinations are designated “ladders,” and it is here proved that the ladder structure is invariant with order when the order is decreased from its permissible maximum value for the corresponding ladder. In view of Wechsung's demonstration that the functions of sixth and higher orders possess no functional equations of Kummer's type, this analytical proof is currently limited to a maximum of the fifth order. The invariance property does not necessarily persist in reverse—increasing the order need not produce a valid ladder with rational coefficients. Nevertheless, quite a number of low-order ladders do lend themselves to such extension, with the needed additional rational coefficients being determined by numerical computation. With sufficient accuracy there is never any doubt as to the rational character of the numbers ensuing from this process. This method of extrapolation to higher orders has led to many quite new results; although at this time completely lacking any analytical proof. Even more astonishing, in view of Wechsung's theorem mentioned above, is the fact that in some cases the ladders can be validly extended beyond the fifth order. This has led to the first-ever results for polylogarithms of order six through nine. A meticulous attention to the finer points in the formulas was necessary to achieve these results; and a number of conjectural rules for extrapolating ladders in this way has emerged from this study. Although it is known that the polylogarithm does not possess any relations of a polynomial character with rational coefficients between the different orders, such relations do exist for some of the ladder structures. A number of examples are given, together with a representative sample of ladders of both the analytical and numerically-verified types. The significance of these new and striking results is not clear, but they strongly suggest that polylogarithmic functional equations, of a more far-reaching character than those currently known, await discovery; probably up to at least the ninth order.     

Permutation polynomials over algebraic number fields

Let K be an algebraic number field. It is known that any polynomial which induces a permutation on infinitely many residue class fields of K is a composition of cyclic and Chebyshev polynomials. This paper deals with the problem of deciding, for a given K, which compositions of cyclic or Chebyshev polynomials have this property. The problem is reduced to the case where K is an Abelian extension of $\text{Q}$. Then the question is settled for polynomials of prime degree, and the Abelian case for composite degree polynomials is considered. Finally, various special cases are dealt with.     

Character sums in algebraic number fields

The Pólya-Vinogradov inequality is generalized to arbitrary algebraic number fields K of finite degree over the rationals. The proof makes use of Siegel's summation formula and requires results about Hecke's zeta-functions with Grössencharacters. One application is to the problem of estimating a least totally positive primitive root modulo a prime ideal of K, least in the sense that its norm is minimal.