Depth for complexes, and intersection theorems

This paper introduces a new notion of depth for complexes; it agrees with the classical definition for modules, and coincides with earlier extensions to complexes, whenever those are defined. Techniques are developed leading to a quick proof of an extension of the Improved New Intersection Theorem (this uses Hochster's big Cohen-Macaulay modules), and also a generalization of the “depth formula” for tensor product of modules. Properties of depth for complexes are established, extending the usual properties of depth for modules. Received May 6, 1997; in final form December 3, 1997     

Rationality for generic toric rings

We study generic toric rings. We prove that they are Golod rings, so the Poincaré series of the residue field is rational. We classify when such a ring is Koszul, and compute its rate. Also resolutions related to the initial ideal of the toric ideal with respect to reverse lexicographic order are described. Received August 13, 1997; in final form October 23, 1998     

A note on Property Np

Let M be a very ample line bundle on a smooth complex projective variety Y and let ϕ _M :Y→P(H ⁰(Y, M)^*) be the map associated to M; we are concerned with the problem to see whether the syzygies of ϕ _M (Y) give information on the syzygies of ϕ _M ^s (Y). In particular we prove that if Y is a smooth complex projective variety and M is a line bundle on Y satisfying Property N _p , then M ^s satisfies Property N _p if s≥p. Received: 11 June 1999 / Revised version: 22 November 1999     

Constant curved minimal 2-spheres in G(2,4)

This paper gives a complete classification for minimal 2-spheres with constant Gaussian curvature immersed in the complex Grassmann manifold G(2,4). Received: 14 May 1998 / Revised version: 12 October 1998     

Separable integral extensions and plus closure

We show that an excellent local domain of characteristic p has a separable big Cohen–Macaulay algebra. In the course of our work we prove that an element which is in the Frobenius closure of an ideal can be forced into the expansion of the ideal to a module-finite separable extension ring. Received: 28 May 1998 / Revised version: 30 November 1998     

On the integral closure of ideals

Among the several types of closures of an ideal I that have been defined and studied in the past decades, the integral closure has a central place being one of the earliest and most relevant. Despite this role, it is often a difficult challenge to describe it concretely once the generators of I are known. Our aim in this note is to show that in a broad class of ideals their radicals play a fundamental role in testing for integral closedness, and in case , is still helpful in finding some fresh new elements in . Among the classes of ideals under consideration are: complete intersection ideals of codimension two, generic complete intersection ideals, and generically Gorenstein ideals. Received: 28 July 1997     

Functors of log Artin rings

This paper gives a generalization of the theory of functors of Artin rings in the framework of log geometry. In the final section we apply it to the log smooth deformation theory. Received: 4 August 1997 / Revised version: 13 January 1998     

The similarity degree of an operator algebra, II

For every integer , there is a unital closed subalgebra with similarity degree equal precisely to d, in the sense of our previous paper. This means that for any unital homomorphism we have with independent of u, and the exponent d in this estimate cannot be improved. The proof that the degree is larger than crucially uses an upper bound for the norms of certain Gaussian random matrices due to Haagerup and Thorbj?rnsen. We also include several complements to our previous publications on the same subject. Received: 25 April, 1999; Accepted: 23 June, 1999     

Flow of diffeomorphisms induced by a geometric multiplicative functional

In this paper it is shown that the unique multiplicative functional solution to a differential equation driven by a geometric multiplicative functional consitutes a flow of local diffeomorphisms. In the case where the driving geometric multiplicative functional is generated by a Brownian motion, the result in particular presents an answer to an open problem proposed in Ikeda and Watanabe [4]. Received: 6 May 1996 / Revised version: 20 March 1998     

Spinning analytic discs and domains of dependence

In this paper we introduce a new technique of spinning analytic discs, which allows us to control the direction of CR extension of CR functions from rigid CR manifolds. Received: 30 January 1998     

Uniqueness of Gibbs states for quantum lattice systems

Summary. We prove uniqueness of Euclidean Gibbs states for certain quantum lattice systems with unbounded spins. We use Dobrushin’s uniqueness criterion. The necessary estimates for the Vasershtein distance between the corresponding one-point conditional distributions with boundary conditions differing only at one side, are obtained by proving a Log-Sobolev inequality on the infinite dimensional single spin (= loop) spaces. Some important classes of concrete examples to which all this applies are discussed. Received: 28 February 1996 / In revised form: 9 September 1996     

A note on nonstable monomorphisms¶of vector bundles

In this paper we consider the question of the existence of a nonstable vector bundle monomorphism u:α→β over a closed, connected and smooth manifold M, when dimension of α= 3, dimension of β= dimension of M=n≡ 0(4). The singularity method provides the full obstruction to this problem and under some homological hypothesis we can compute it in terms of well known invariants. Received: 31 May 1999