Mathematics

The aim of this note is firstly to give a new brief proof of classical Bochner's Tube Theorem (1938) by making use of K. Oka's Boundary Distance Theorem (1942), showing directly that two points of the envelope of holomorphy of a tube can be connected by a line segment. We then apply the same idea to show that if an unramified domain D:= A 1 +i A 2 → C n with unramified real domains A j → R n is pseudoconvex, then the both A j are univalent and convex (a generalization of Kajiwara's theorem). From the viewpoint of this result we discuss a generalization by M. Abe with giving an example of a finite tube over C n for which Abe's theorem no longer holds. The present method may clarify the point where the (affine) convexity comes from.

We will show a rigidity of a Kähler potential of the Poincaré metric with a constant length differential.

By proving an estimate of the sublevel sets for (ω,m) -subharmonic functions we obtain a Sobolev type inequality that is then used to characterize the degenerate complex Hessian equations for such functions with bounded (p,m) -energy.

In 2016, the Hurwitz metric was introduced by D. Minda in arbitrary proper subdomains of the complex plane and he proved that this metric coincides with the Poincaré's hyperbolic metric when the domains are simply connected. In this paper, we provide an alternate definition of the Hurwitz metric through which we could define a generalized Hurwitz metric in arbitrary subdomains of the complex plane. This paper mainly highlights various important properties of the Hurwitz metric and the generalized metric including the situations where they coincide with each other.

After their introduction in 2006, quaternionic slice regular functions have mostly been studied over domains that are symmetric with respect to the real axis. This choice was motivated by some foundational results published in 2009, such as the Representation Formula for axially symmetric domains. The present work studies slice regular functions over domains that are not axially symmetric, partly correcting the hypotheses of some previously published results. In particular, this work includes a Local Representation Formula valid without the symmetry hypothesis. Moreover, it determines a class of domains, called simple, having the following property: every slice regular function on a simple domain can be uniquely extended to the symmetric completion of its domain.

In this note we establish a lower bound for the distance induced by the Kähler-Einstein metric on pseudoconvex domains with positive hyperconvexity index (e.g. positive Diederich-Fornaess index). A key step is proving an analog of the Hopf lemma for Riemannian manifolds with Ricci curvature bounded from below.

A generalization of the homological Poincare's operator was used to estimate the dimension of the Lie algebra of infinitesimal holomorphic automorphisms of an arbitrary germ of a real analytic hypersurface in C 4 . The following alternative is proved: either this dimension is infinite, or it does not exceed 24. Value 24 takes place only for one of two nondegenerate hyperquadrics. If the hypersurface is 2-nondegenerate at a generic point, then the dimension does not exceed 17, and if the hypersurface is 3-nondegenerate at a generic point, then the estimate is 20.

In 1979 I. Cior?nescu and L. Zsidó have proved a minimum modulus theorem for entire functions dominated by the restriction to the positive half axis of a canonical product of genus zero, having all roots on the positive imaginary axis and satisfying a certain condition. Here we prove that the above result is optimal: if a canonical product {\omega} of genus zero, having all roots on the positive imaginary axis, does not satisfy the condition in the 1979 paper, then always there exists an entire function dominated by the restriction to the positive half axis of {\omega}, which does not satisfy the desired minimum modulus conclusion. This has relevant implication concerning the subjectivity of ultra differential operators with constant coefficients.

In this paper we establish several invariant boundary versions of the (infinitesimal) Schwarz-Pick lemma for conformal pseudometrics on the unit disk and for holomorphic selfmaps of strongly convex domains in C N in the spirit of the boundary Schwarz lemma of Burns-Krantz. Firstly, we focus on the case of the unit disk and prove a general boundary rigidity theorem for conformal pseudometrics with variable curvature. In its simplest cases this result already includes new types of boundary versions of the lemmas of Schwarz-Pick, Ahlfors-Schwarz and Nehari-Schwarz. The proof is based on a new Harnack-type inequality as well as a boundary Hopf lemma for conformal pseudometrics which extend earlier interior rigidity results of Golusin, Heins, Beardon, Minda and others. Secondly, we prove similar rigidity theorems for sequences of conformal pseudometrics, which even in the interior case appear to be new. For instance, a first sequential version of the strong form of Ahlfors' lemma is obtained. As an auxiliary tool we establish a Hurwitz-type result about preservation of zeros of sequences of conformal pseudometrics. Thirdly, we apply the one-dimensional sequential boundary rigidity results together with a variety of techniques from several complex variables to prove a boundary version of the Schwarz-Pick lemma for holomorphic maps of strongly convex domains in C N for N>1 .

Recently the author has presented a new approach to solving extremal problems of geometric function theory. It involves the Bers isomorphism theorem for Teichmuller spaces of punctured Riemann surfaces. We show here that this approach, combined with quasiconformal theory, can be also applied to nonvanishing holomorphic functions from H ∞ . In particular this gives a proof of an old open Krzyz conjecture for such functions and of its generalizations. The unit ball H ∞ 1 of H ∞ is naturally embedded into the universal Teichmuller space, and the functions f∈ H ∞ 1 are regarded as the Schwarzian derivatives of univalent functions in the unit disk.