Abstract: | The paper is devoted to the determination of an analog of J, von Neumann's inequality for the space Lp.The fundamental result of the paper is: If T is an absolute contraction in the space Lp(X,F,μ) (i.e., |T|L1≤1) and |T|L∞≤1) then for every polynomial ϕ one has
where S is the shift operator in the space. On the basis of this theorem, one finds a theorem on substitutions in the space
of multipliers. One gives applications of the inequality (1) to the weighted shift operators in the space It turns out that
under some natural restrictions on the weight, inequality (1) becomes an equality for such operators. One also presents a
proof of J. von Neumann's inequality based on the approximation of a contraction in a Hilbert space by unitary operators.
Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR,
Vol. 65, pp. 133–148, 1976.
The author wishes to express his thanks to N. K. Nikol'skii for suggesting the problem and for his interest in the paper. |