# zbMATH — the first resource for mathematics

Kobayashi, Carathéodory and Sibony metric. (English) Zbl 1166.32010
The order of growth for the Sibony differential metric $$F_{\Omega}^S$$ on a $$C^2$$-smooth bounded domain $$\Omega$$ in $$\mathbb C^n$$ is determined near a pseudoconcave boundary point and compared with that of the differential metrics of Caratheodory and Kobayashi, which will be denoted by $$F_{\Omega}^C$$ and $$F_{\Omega}^K$$, respectively. Let $$A_{\Omega}(P)$$ denote for a point $$P \in \Omega$$ the set of all plurisubharmonic functions $$u:\Omega \to [0,1]$$, such that $$u(P)=0$$, and $$\log u$$ is also plurisubharmonic. Then the metric $$F_{\Omega}^S$$ is given by
$F_{\Omega}^S (P;X) := \sup \{ \sqrt{(\partial \bar \partial u (P) X,X)} \,|\, u \in A_{\Omega}(P)\} ,\qquad P \in \Omega,\,\,X \in \mathbb C^n.$
The result is as follows:
Theorem: Let $$P \in \partial \Omega$$ be a non-pseudoconvex point and $$P_\delta$$ the point on the inner normal to $$\partial \Omega$$ at $$P$$ with boundary distance $$\delta$$ and $$\nu$$ the inner unit normal at $$P$$. Then
$F_{\Omega}^S(P_\delta, \nu ) \approx \frac{1}{\sqrt{\delta}},\qquad F_{\Omega}^C(P_\delta, \nu ) \approx 1.$
Together with the estimate
$F_{\Omega}^K(P_\delta, \nu ) \approx \frac{1}{\delta^{3/4}}$
which is due to S. Krantz, it follows that the orders of growth for these differential metrics are pairwise different in this situation.
The main lemma in the proof of the above theorem is the following estimate on $$F_{\Omega}^S$$ for the ring domain
$\Omega_m :=\{ \frac{1}{4} < |z|^2+|w|^m <3\},\qquad m \geq 2$ at the point $$p_\delta := ( \frac{1}{2}+\delta , 0)$$, namely
$F_{\Omega_m}^S (p_\delta , \left(\begin{matrix} 1 \\ 0 \end{matrix} \right) \,) \approx \frac{1}{\delta^{1-\frac{1}{m}}}.$
This result is generalized to the higher dimensional ring domains $\Omega' :=\{ \frac{1}{4} < |z_1|^2+|z_2|^{m_2}+\dots+ |z_n|^{m_n} <1\},\qquad 2 \leq m_2\leq \cdots\leq m_n$ which serve as suitable local domains of comparison at pseudoconcave boundary points.

##### MSC:
 32F45 Invariant metrics and pseudodistances in several complex variables 32U05 Plurisubharmonic functions and generalizations
Full Text:
##### References:
 [1] Krantz SG, Rocky Mountain J. Math. 22 pp 227– (1992) · Zbl 0760.32010 · doi:10.1216/rmjm/1181072807 [2] Fu S, Complex Var. Elliptic Equ. 54 pp 303– (2009) · Zbl 1166.32011 · doi:10.1080/17476930902763819 [3] Fornæss JE, Comparison of the Kobayashi–Royden and Sibony metrics on Ring domains (2008) [4] Kobayashi S, Hyperbolic complex spaces. Grundlehren der Mathematischen Wissenschaften [Fundamental Principles of Mathematical Sciences] 318 (1998) [5] Krantz SG, Function Theory of Several Complex Variables (2001) [6] Royden, HL. Remarks on the Kobayashi metric, Several complex variables, II. Proceedings of the International Conference. 1970, University Maryland, College Park, Md. pp.125–137. Berlin: Springer. Lecture Notes in Math., Vol. 185 [7] Sibony N, Ann. of Math. Stud 100 pp 357– (1981) [8] Graham I, Trans. Amer. Math. Soc. 207 pp 219– (1975)
This reference list is based on information provided by the publisher or from digital mathematics libraries. Its items are heuristically matched to zbMATH identifiers and may contain data conversion errors. It attempts to reflect the references listed in the original paper as accurately as possible without claiming the completeness or perfect precision of the matching.