Searcharxiv⌕ Search

arXiv subjects

Alan Huckleberry

Publications and source records attributed to Alan Huckleberry.

At least 19 recordsLinked to original sources
arXiv2018

Normal bundles of cycles in flag domains

A real semisimple Lie group G_0 embedded in its complexification G has only finitely many orbits in any G-fag manifold Z = G/Q. The complex geometry of its open orbits D (flag domains) is studied from the point of view of compact complex submanifolds C (cycles) which arise as orbits of certain distinguished subgroups. Normal bundles E of the cycles are analyzed in some detail. It is shown that E is trivial if and only if D is holomorphically convex, in fact a product of C and a Hermitian symmetric space, and otherwise D is pseudoconcave.

math.AG↗
arXiv2014

Cycle Connectivity and Automorphism Groups of Flag Domains

A flag domain $D$ is an open orbit of a real form $G_0$ in a flag manifold $Z=G/P$ of its complexification. If $D$ is holomorphically convex, then, since it is a product of a Hermitian symmetric space of bounded type and a compact flag manifold, ${Aut}(D)$ is easily described. If $D$ is not holomorphically convex, then in our previous work (American J. Math, 136, Nr.2 (2013) 291-310 (arXiv: 1003.5974)) it was shown that ${Aut}(D)$ is a Lie group whose connected component at the identity agrees with $G_0$ except possibly in situations which arise in Onishchik's list of flag manifolds where ${Aut}(Z)^0$ is larger than $G$. These exceptions are handled in detail here. In addition substantially simpler proofs of some of our previous work are given.

math.CV↗
arXiv2013

Hans Grauert (1930-2011)

Hans Grauert died in September of 2011. This article reviews his life in mathematics and recalls some detail his major accomplishments.

math.HO↗
arXiv2012

Bipartite entanglement, spherical actions and geometry of local unitary orbits

We use the geometry of the moment map to investigate properties of pure entangled states of composite quantum systems. The orbits of equally entangled states are mapped by the moment map on coadjoint orbits of local transformations (unitary transformations which do not change entanglement), thus the geometry of coadjoint orbits provides a partial classification of different entanglement classes. To achieve the full classification a further study of fibers of the moment map is needed. We show how this can be done effectively in the case of the bipartite entanglement by employing Brion's theorem. In particular, we presented the exact description of the partial symplectic structure of all local orbits for two bosons, fermions and distinguishable particles.

math-ph↗
arXiv2011

On the Kobayashi hyperbolicity of certain tube domains

In an earlier article the second author introduced three families of tube domains in ${\mathbf C}^2$ with holomorphic automorphism group isomorphic to ${\mathbf R}\ltimes{\mathbf R}^2$ and envelope of holomorphy equal to ${\mathbf C}^2$. In the present paper we show that every domain in each of these families is Kobayashi-hyperbolic.

math.CV↗
arXiv2010

Selected results on Lie supergroups and their radial operators

Foundational material on complex Lie supergroups and their radial operators is presented. In particular, Berezin's recursion formula for describing the radial parts of fundamental operators in general linear and ortho-symplectic cases is proved. Local versions of results which are suitable for applications for computing characters which are only defined on proper subdomains or covering spaces thereof are established.

math-ph↗
arXiv2010

A method for constructing random matrix models of disordered bosons

Random matrix models of disordered bosons consist of matrices in the Lie algebra g=sp_n(R). Assuming dynamical stability, their eigenvalues are required to be purely imaginary. Here a method is proposed for constructing ensembles (E,P) of G-invariant sets E of such matrices with probability measures P. These arise as moment map direct images from phase spaces X which play an important role in complex geometry and representation theory. In the toy-model case of n=1, where X is the complex bidisk and P is the direct image of the uniform measure, an explicit description of the spectral measure is given.

math-ph↗
arXiv2010

Asymptotics of eigensections on toric varieties

Using exhaustion properties of invariant plurisubharmonic functions along with basic combinatorial information on toric varieties convergence results for sequences of distribution functions ϕ_n=|s_N| / |s_N|_{L^2} for sections s_N\in Γ(X,L^N) approaching a semiclassical ray are proved. Here X is a normal compact toric variety and L is an ample line bundle equipped with an arbitrary positive bundle metric which is invariant with respect to the compact form of the torus.

math.CV↗
arXiv2010

Symplectic geometry of entanglement

We present a description of entanglement in composite quantum systems in terms of symplectic geometry. We provide a symplectic characterization of sets of equally entangled states as orbits of group actions in the space of states. In particular, using Kostant-Sternberg theorem, we show that separable states form a unique Kaehler orbit, whereas orbits of entanglement states are characterized by different degrees of degeneracy of the canonical symplectic form on the complex projective space. The degree of degeneracy may be thus used as a new geometric measure of entanglement and we show how to calculate it for various multiparticle systems providing also simple criteria of separability. The presented method is general and can be applied also under different additional symmetry conditions stemming, eg. from the indistinguishability of particles.

math-ph↗
arXiv2010

Remarks on homogeneous manifolds satisfying Levi conditions

Homogeneous complex manifolds satisfying various types of Levi conditions are considered. Classical results which were of particular interest to Andreotti are recalled. Convexity and concavity properties of flag domains are discussed in some detail. A precise classification of pseudoconvex flag domains is given. It is shown that flag domains which are in a certain sense generic are pseudoconcave.

math.CV↗
arXiv2010

Hyperbolicity of cycle spaces and automorphism groups of flag domains

If G_0 is a real form of a complex semisimple Lie group G and Z is compact G-homogeneous projective algebraic manifold, then G_0 has only finitely many orbits on Z. Complex analytic properties of open G_0-orbits D (flag domains) are studied. Schubert incidence-geometry is used to prove the Kobayashi hyperbolicity of certain cycle space components C_q(D). Using the hyperbolicity of C_q(D) and analyzing the action of Aut(D) on it, an exact description of Aut(D) is given. It is shown that, except in the easily understood case where D is holomorphically convex with a nontrivial Remmert reduction, it is a Lie group acting smoothly as a group of holomorphic transformations on D. With very few exceptions it is just G_0.

math.CV↗
arXiv2010

Karl Stein (1913-2000)

Karl Stein was one of the pillars of the German school of several complex variables. In this article his scientific contributions are outlined in historical perspective.

math.HO↗
arXiv2010

Hans Grauert: Mathematician Pur

This article was written on the occasion of Hans Grauert receiving the Cantor Medallion of the Deutsche Mathematische Vereinigung. It is a brief overview of his mathematical contributions and attempts to convey the author's great respect for the man and his science.

math.HO↗
arXiv2009

Finite symmetry groups in complex geometry

On June 5, 2007 the second author delivered a talk at the Journees de l'Institut Elie Cartan entitled "Finite symmetry groups in complex geometry". This paper begins with an expanded version of that talk which, in the spirit of the Journees, is intended for a wide audience. The later paragraphs are devoted both to the exposition of basic methods, in particular an equivariant minimal model program for surfaces, as well as an outline of recent work of the authors on the classification of K3-surfaces with special symmetry.

math.AG↗
arXiv2009

Classical Symmetries of Complex Manifolds

We consider complex manifolds that admit actions by holomorphic transformations of classical simple real Lie groups and classify all such manifolds in a natural situation. Under our assumptions, which require the group at hand to be dimension-theoretically large with respect to the manifold on which it is acting, our classification result states that the manifolds which arise are described precisely as invariant open subsets of certain complex flag manifolds associated to the complexified groups.

math.CV↗
arXiv2008

Cycle Space Constructions for Exhaustions of Flag Domains

In the study of complex flag manifolds, flag domains and their cycle spaces, a key point is the fact that the cycle space $\mathcal M_D$ of a flag domain $D$ is a Stein manifold. That fact has a long history. The earliest approach relied on construction of a strictly plurisubharmonic function on $\mathcal M_D$, starting with a $q$--convex exhaustion function on $D$, where $q$ is the dimension of a particular maximal compact subvariety of $D$ (we use the normalization that 0--convex means Stein). Construction of that exhaustion function on $D$ required that $D$ be measurable. In that case the exhaustion on $D$ was transferred to $\mathcal M_D$, using a special case of a method due to Barlet. Here we do the opposite: we use an incidence method to construct a canonical plurisubharmonic exhaustion function on $\mathcal M_D$ and use it in turn to construct a canonical $q$--convex exhaustion function on $D$. This promises to have strong consequences for cohomology vanishing theorems and the construction of admissible representations of real reductive Lie groups.

math.CV↗