<Emphasis Type="Italic">L</Emphasis><Superscript><Emphasis Type="Italic">p</Emphasis></Superscript> estimates for the biest II. The Fourier case

We prove L^p estimates (Theorem 1.2) for the biest, a trilinear multiplier operator with singular symbol. The methods used are based on the treatment of the Walsh analogue of the biest in the prequel [13] of this paper, but with additional technicalities due to the fact that in the Fourier model one cannot obtain perfect localization in both space and frequency.     

Convexity and <Emphasis Type="Italic">w</Emphasis><Superscript><Emphasis Type="Italic">*</Emphasis></Superscript>-compactness in Banach spaces

Suppose X. We construct examples of bounded sets MX, such that These examples show that the previous results of the authors on quantitative versions of Kreins theorem are optimal.Mathematics Subject Classification (2000):46B20, 46B26A. S. Granero supported by DGICYT grant BFM2001-1284. P. Hájek supported by GAR 201/01/1198, A 101 92 05 and UPV grant PPI-02-02.     

The intersection of complete geodesics on <Emphasis Type="Italic">S</Emphasis><Superscript>2</Superscript> with positive curvature

Let M be a Riemannian manifold. A complete geodesic on M means that :(-,+)M is a normalized geodesic. In this paper, we prove that on (S²,g) with positive curvature, any two complete geodesics must intersect an infinite number of times, and a complete geodesic must self-intersect an infinite number of times. Mathematics Subject Classification (2000) 53C40 (53C22)     

Biharmonic maps from <Emphasis Type="Italic">R</Emphasis><Superscript><Emphasis Type="Italic">4</Emphasis></Superscript> into a Riemannian manifold

For a domain R⁴ and a compact Riemannian manifold NR^k without boundary, if uW^2,2(,N) is an extrinsic (or intrinsic, respectively) biharmonic map, then uC(,N).in final form: 1 August 2003     

Shape-preserving Kolmogorov widths of classes of <Emphasis Type="Italic">s</Emphasis>-monotone integrable functions

Let s ₀ and let ₊ ^s be the set of functions x defined on a finite interval I and such that, for all collections of s + 1 pairwise different points t ₀,..., t _s I, the corresponding divided differences [x; t ₀,...,t _s ] of order s are nonnegative. Let ₊ ^s B _{p +} ^s B _p, 1 p where B _p is a unit ball in the space L _p, and let ₊ ^s L _{q +} ^s L _q, 1 q . For every s 3 and 1 q p , we determine the exact orders of the shape-preserving Kolmogorov widths {x - y} \right\ L_q , $$]]>, where M ⁿ is the collection of all affine linear manifolds M ⁿ in L _q such that dim M ⁿ n and M ⁿ ₊ ^s L _q .Translated from Ukrainskyi Matematychnyi Zhurnal, Vol. 56, No. 7, pp. 901–926, July, 2004.     

Bipartite <Emphasis Type="Italic">Q</Emphasis>-Polynomial Distance-Regular Graphs

Let denote a bipartite distance-regular graph with diameter D12. We show is Q-polynomial if and only if one of the following (i)–(iv) holds: (i) is the ordinary 2D-cycle. (ii) is the Hamming cube H(D,2). (iii) is the antipodal quotient of H(2D,2). (iv) The intersection numbers of satisfy where q is an integer at least 2. We obtain the above result using the Terwilliger algebra of .AMS 1991 Subject Classification: Primary 05E30Final version received: April 10, 2003     

Two variable <Emphasis Type="Italic">p</Emphasis>-adic <Emphasis Type="Italic">L</Emphasis> functions attached to eigenfamilies of positive slope

Consider a classical cusp eigenform f= _n=1 a _n (f)q ⁿ of weight k2 for ₀(N) with a Dirichlet character mod N, and let L _f (s,)= _n=1 (n)a _n (f)n ^-s denote the L-function of f twisted with an arbitrary Dirichlet character . For a prime number p5, consider a family of cusp eigenforms f _(k) of weight k , k {f _(k)= _n=1 a _n (f _(k))q ⁿ } containing f=f _(k), such that the Fourier coefficients a _n (f _(k)) are given by certain p-adic analytic functions k a _n (f _(k)). The purpose of this paper is to construct a two variable p-adic L function attached to Colemans family {f _(k)} of cusp eigenforms of a fixed positive slope =v _p ( _p )>0 where _p = _p (k ) is an eigenvalue (which depends on k ) of the Atkin operator U=U _p . Our p-adic L-function interpolates the special values L _f(k)(s,) at points (s,k ) with s=1,2,...,k -1. We give a construction using the Rankin-Selberg method and the theory of p-adic integration on a profinite group Y with values in an affinoid K-algebra A, where K is a fixed finite extension of Q _p . Our p-adic L-functions are p-adic Mellin transforms of certain A-valued measures. In their turn, such measures come from Eisenstein distributions with values in certain Banach A-modules M =M (N;A) of families of overconvergent forms over A. To Robert Alexander Rankin in memoriam     

Continuation of <Emphasis Type="Italic">L</Emphasis><Superscript>2</Superscript>-holomorphic functions

Let be a bounded domain in Cⁿ and let L²_h() be the L²-holomorphic functions on . We show that the envelope of holomorphy and the L²_h()-envelope of holomorphy of differ by at most a pluripolar set.Mathematics Subject Classification (2000): 32D10, 32A36, 32U30This article is based on work the author did during his Ph.D. studies at the University of Michigan under the supervision of John Erik Fornæss.     

Surfaces of general type with <Emphasis Type="Italic">p</Emphasis><Subscript><Emphasis Type="Italic">g</Emphasis></Subscript>=0, <Emphasis Type="Italic">K</Emphasis><Superscript>2</Superscript>=6 and non birational bicanonical map

Let S be a minimal surface of general type with p_g=0 and K²=6, such that its bicanonical map is not birational. The map is a morphism of degree 4 onto a surface. The case of deg = 4 is completely classified in [Topology, 40 (5) (2001), 977–991] and the present paper completes the characterization of these surfaces. It is proven that the degree of cannot be equal to 3, and the geometry of surfaces with deg = 2 is analysed in detail. The last section contains three examples of such surfaces, two of which appear to be new.Mathematics Subject Classification (2000): 14J29     

<Emphasis Type="Italic">K</Emphasis>-homology of <Emphasis Type="Italic">C</Emphasis><Superscript><Emphasis Type="Italic">*</Emphasis></Superscript>-categories and symmetric spectra representing <Emphasis Type="Italic">K</Emphasis>-homology

We define K-homology groups K _* () for small C ^* -categories in terms of Hilbert modules over the C ^* -category . We also define a functor A ^f from the category of small C ^* -categories into the category of C ^* -algebras and show that there is a natural isomorphism . In addition, we give an easy construction of a functor from the category of C ^* -algebras into the category of symmetric spectra which represents K-homology, i.e. we show that the functor comes with a natural isomorphism for C ^* -algebras A. It then follows that the composition A ^f provides a functor that can be used in the Davis-Lück approach for constructing the Baum-Connes map.     

Hardy algebras, <Emphasis Type="Italic">W</Emphasis>*-correspondences and interpolation theory

Given a von Neumann algebra M and a W*-correspondence E over M, we construct an algebra H(E) that we call the Hardy algebra of E. When M= =E, H(E) is the classical Hardy space H of bounded analytic functions on the unit disc. When M= and E= H(E) is the free semigroup algebra studied by Popescu, Davidson and Pitts and many others. We show that given any faithful normal representation of M on a Hilbert space H there is a natural correspondence E over the commutant (M), called the -dual of E, and that H(E) can be realized in terms of (B(H)-valued) functions on the open unit ball ((E)*) in the space of adjoints of elements in E. We prove analogues of the Nevanlinna-Pick theorem in this setting and discover other aspects of the value distribution theory for elements in H(E). We also analyze the boundary behavior of elements in H(E) and obtain generalizations of the Sz.-Nagy–Foia functional calculus and the functional calculus of Popescu for c.n.c. row contractions. The correspondence E has a dual that is naturally isomorphic to E and the commutants of certain, so-called induced representations of H(E) can be viewed as induced representations of H(E). For these induced representations a double commutant theorem is proved.Supported in part by grants from the National Science Foundation and from the U.S.-Israel Binational Science Foundation.Supported in part by the U.S.-Israel Binational Science Foundation and by the Fund for the Promotion of Research at the Technion.Revised version: 11 March 2004     

Weighted <Emphasis Type="Italic">L</Emphasis><Superscript><Emphasis Type="Italic">p</Emphasis></Superscript> Boundedness of Marcinkiewicz Integral

A weighted norm inequality for the Marcinkiewicz integral operator is proved when belongs to . We also give the weighted L^p-boundedness for a class of Marcinkiewicz integral operators with rough kernels and related to the Littlewood-Paley -function and the area integral S, respectively.     

PL Homeomorphisms of the circle which are piecewise <Emphasis Type="Italic">C</Emphasis><Superscript>1</Superscript> conjugate to irrational rotations

For a PL homeomorphism f with irrational rotation number , the following properties are equivalent(i) f is conjugate to the rotation by through a piecewise C ¹ homeomorphism,(ii) the number of break points of f ⁿ is bounded by some constant that doesnt depend on n,(iii) f is conjugate to an affine 2-intervals exchange transformation (with rotation number ) through a PL homeomorphism,(iv) f is conjugate to the rotation by through a piecewise analytic homeomorphism.     

Small Ball Estimates in <Emphasis Type="Italic">p</Emphasis>-Variation for Stable Processes

Let Z _t , t 0 be a strictly stable process on with index (0, 2]. We prove that for every p > , there exists = _{, p} and such that

A space <Emphasis Type="Italic">C</Emphasis><Subscript><Emphasis Type="Italic">p</Emphasis></Subscript>(<Emphasis Type="Italic">X</Emphasis>) is dominated by irrationals if and only if it is<Emphasis Type="Italic"> K</Emphasis>-analytic

Summary We prove that, for any Tychonoff X, the space C_p(X) is K-analytic if and only if it has a compact cover {K_p: p } such that K_p subset K_q whenever p,q and p q. Applying this result we show that if C_p(X) is K-analytic then C_p(X) is K-analytic as well. We also establish that a space C_p(X) is K-analytic and Baire if and only if X is countable and discrete.     

The <Emphasis Type="Italic">p</Emphasis>-harmonic approximation and the regularity of <Emphasis Type="Italic">p</Emphasis>-harmonic maps

We extend to the degenerate case , Simons approach to the classical regularity theory of harmonic maps of Schoen & Uhlenbeck, by proving a p-Harmonic Approximation Lemma. This allows to approximate functions with p-harmonic functions in the same way as the classical harmonic approximation lemma (going back to De Giorgi) does via harmonic functions. Finally, we show how to combine this tool with suitable regularity estimates for solutions to degenerate elliptic systems with a critical growth right hand side, in order to obtain partial -regularity of p-harmonic maps.Received: 2 November 2002, Accepted: 10 July 2003, Published online: 4 September 2003Mathematics Subject Classification (2000): 35J70, 49N60, 49Q60     

Partition of <Emphasis Type="Italic">C</Emphasis><Subscript>4</Subscript>-Designs into Minimum and Maximum Number of <Emphasis Type="Italic">P</Emphasis><Subscript>3</Subscript>-Designs

Let be a C₄-design of order n and index , on the vertex set V, |V|=n. If V₁V_m=V is a partition of the vertex set, such that the intersections of the with V_i form a P₃-design of order |V_i| and the same index , for each 1im, then 2m log₃(2n+1). The minimum bound is best possible for every . The maximum bound is best possible for =2, and hence also for every even .Supported by MIUR, Italy and CNR-GNSAGAAlso affiliated with the Department of Computer Science, University of Veszprém, Hungary; supported in part by the Hungarian Scientific Research Fund, grant OTKA T-32969AMS classification: 05B05     

Asymptotic estimates of Dirac and Laplace eigenvalues on warped products over <Emphasis Type="Italic">S</Emphasis><Superscript><Emphasis Type="Italic">1</Emphasis></Superscript>

In this paper we show that the space of spinors over a warped product over S ¹ has a certain splitting =W(k,n) in spaces of spinors of weight k and winding number n which is respected by the Dirac operator. The same holds for the space of functions and the Laplace operator. We give eigenvalue estimates for the eigenvalues _k,n of the Dirac operator with eigenspinors of weight k and winding number n and eigenvalues _m,n of the Laplace operator with eigenfunctions of weight m and winding number n. In particular, we show that ² _k,n ² _k,n holds for large n on S ¹ × _fT ^l where T ^l is a flat torus with the trivial spin structure. Mathematics Subject Classification (2000):34L20, 53C21, 58J50, 58J60     

A criterion for <Emphasis Type="Italic">C</Emphasis><Superscript>2</Superscript>-rectifiability of sets

The following result is proved: Let be a n-dimensional C¹-submanifold of R^N which is domain of a given _nR^N-valued map of class C¹. Then the set of all points P such that (P) is non-zero, simple and enveloped by T_P is C²-rectifiable. As a corollary we get a criterion for the C²-rectifiability of a rectifiable set based on the rectifiability of some generalized Gauss lift to the Grassmanian bundle R^N×G(N,n). Mathematics Subject Classification (2000) Primary 49Q15, 53A07; Secondary 49Q20, 49N60     

On Paley-Wiener and Hardy theorems for <Emphasis Type="Italic">NA</Emphasis> groups

Let N be a H-type group and let S=NA be an one dimensional solvable extension of N. For the Helgason Fourier transform on S we prove the following analogue of Hardys theorem. Let (,Y,Z) stand for the Helgason Fourier transform of f and let h denote the heat kernel associated to the Laplace-Beltrami operator. Suppose a function f on S satisfies the conditions |f(x)| ch (x) and for all xS, where being the dimension of the centre of N. Then f=0 or f=ch depending on whether < or =. We also establish a stronger version of Hardys theorem and a Paley-Wiener theorem. These are generalisations of the corresponding results for rank one symmetric spaces of noncompact type.