解析学火曜セミナー

過去の記録 ~02/04次回の予定今後の予定 02/05~

開催情報 火曜日 16:00~17:30 数理科学研究科棟(駒場) 126号室
担当者 石毛 和弘, 坂井 秀隆, 伊藤 健一
セミナーURL https://www.ms.u-tokyo.ac.jp/seminar/analysis/

2015年09月29日(火)

16:50-18:20   数理科学研究科棟(駒場) 126号室
Otto Liess 氏 (University of Bologna, Italy)
On the Phragmén-Lindelöf principle for holomorphic functions and factor classes of higher order complex forms in several complex variables
[ 講演概要 ]
In this talk we will discuss maximum principles in unbounded domains in one or several complex variables. We will mainly be interested in these principles for plurisubharmonic (in the one-dimensional case, "subharmonic") or holomorphic functions, when the principles are of
Phragmen-Lindel{\"o}f principle (henceforth called "PL") type. It will turn out that for 2 or more complex variables it will be useful to study our principles together with associated principles for factor classes of complex (0,q) forms with growth type conditions at infinity.
In this abstract we only say something concerning the case of functions. We consider then an open set U in C^n in one or several complex variables. We assume that we are given two real-valued continuous functions f and g on U. We say that PL holds for plurisubharmonic (respectively for holomorphic) functions, if the following implication is true for every plurisubharmonic function $ \rho $ (respectively for every $ \rho $ of form log |h| with h holomorphic) on U: if we know that $ \rho \leq f$ on the boundary of U and if $ (\rho - f)$ is bounded on U, then it must follow that $ \rho \leq g$ on U. ($\rho \leq f$ on the boundary has the following meaning: for ever z in the boundary of U and for every sequence of points y_j in U which tends to z, we have limsup (\rho - f)(y_j) leq 0.) A trivial condition under which PL is true, is when there exists a plurisubharmonic function u on U such that
(*) -g(z) \leq u(z) \leq - f(z) for every z in U.
In fact, if such a function exists, then we can apply the classical maximal principle for unbounded domains to the function $ \rho'= \rho+u$ to obtain at first $ \rho' \leq 0$ and then $ \rho \leq - u \leq g$. It is one of the main goals of the talk to explain how far (*) is from being also a necessary condition for PL. Some examples are intended to justify our approach and applications will be given to problems in convex analysis.