Abstract
Let (X, μ) and (Y, ν) be standard measure spaces. A function \({\varphi\in L^\infty(X\times Y,\mu\times\nu)}\) is called a (measurable) Schur multiplier if the map S φ , defined on the space of Hilbert-Schmidt operators from L 2(X, μ) to L 2(Y, ν) by multiplying their integral kernels by φ, is bounded in the operator norm. The paper studies measurable functions φ for which S φ is closable in the norm topology or in the weak* topology. We obtain a characterisation of w*-closable multipliers and relate the question about norm closability to the theory of operator synthesis. We also study multipliers of two special types: if φ is of Toeplitz type, that is, if φ(x, y) = f(x − y), \({x,y\in G}\), where G is a locally compact abelian group, then the closability of φ is related to the local inclusion of f in the Fourier algebra A(G) of G. If φ is a divided difference, that is, a function of the form (f(x) − f(y))/(x − y), then its closability is related to the “operator smoothness” of the function f. A number of examples of non-closable, norm closable and w*-closable multipliers are presented.
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References
Arveson W.B.: Operator algebras and invariant subspaces. Ann. Math. (2) 100, 433–532 (1974)
Birman M.S., Solomyak M.Z.: Stieltjes double-integral operators. II (Russian). Prob. Mat. Fiz. 2, 26–60 (1967)
Birman M.S., Solomyak M.Z.: Stieltjes double-integral operators, III (Passage to the limit under the integral sign) (Russian). Prob. Mat. Fiz. 6, 27–53 (1973)
Birman M.S., Solomyak M.Z.: Operator integration, perturbations and commutators. Zap. Nauchn. Sem. Leningrad. Otdel. Mat. Inst. Steklov. (LOMI) Issled. Linein. Oper. Teorii Funktsii. 17(170), 34–66 (1989)
Birman M.S., Solomyak M.Z.: Double operator integrals in a Hilbert space. Integr. Equ. Oper. Theory 47(2), 131–168 (2003)
Blecher D.P., Smith R.: The dual of the Haagerup tensor product. J. Lond. Math. Soc. (2) 45, 126–144 (1992)
Bozejko M., Fendler G.: Herz-Schur multipliers and completely bounded multipliers of the Fourier algebra of a locally compact group. Colloquium Math. 63, 311–313 (1992)
Comfort W.W., Gordon H.: Vitali’s theorem for invariant measures. Trans. Am. Math. Soc. 99, 83–90 (1961)
Daletskii J.L., Krein S.G.: Integration and differentiation of functions of hermitian operators and applications to the theory of perturbations. Am. Math. Soc. Transl. (2) 47, 1–30 (1965)
Erdos J.A., Katavolos A., Shulman V.S.: Rank one subspaces of Bimodules over maximal abelian selfadjoint algebras. J. Funct. Anal. 157(2), 554–587 (1998)
Farforovskaya, Y.B.: An estimate of the norm ||f(A) − f(B)|| for selfadjoint operators A and B. Zap. Nauchn. Semin. LOMI 56, 143–162 (1976). (English transl. J. Sov. Math. 14, 1133–1149) (1980)
Froelich J.: Compact operators, invariant subspaces and spectral synthesis. J. Funct. Anal. 81, 1–37 (1988)
Gelfand I., Raikov D., Shilov G.: Commutative Normed Rings. Translated from the Russian, with a Supplementary Chapter. Chelsea Publishing Co., New York (1964)
Gohberg, I.C., Krein, M.G.: Theory and Applications of Volterra Operators in Hilbert Space. Translation of Mathematical Monographs, vol. 24. American Mathematical Society (1970)
Graham C., McGehee O.C.: Essays in Commutative Harmonic Analysis. Springer-Verlag, New York (1979)
Grothendieck A.: Resume de la theorie metrique des produits tensoriels topologiques. Boll. Soc. Mat. Sao-Paulo 8, 1–79 (1956)
Hewitt E., Ross K.A.: Abstract Harmonic Analysis, vol. I. Structure of Topological Groups, Integration Theory, Group Representations. Springer- Verlag, Berlin (1979)
Hewitt E., Stromberg K.: Real and Abstract Analysis. A Modern Treatment of the Theory of Functions of a Real Variable. Springer-Verlag, New York (1965)
Kato T.: Perturbation Theory for Linear Operators. Springer-Verlag, Berlin (1995)
Katznelson Y.: An Introduction to Harmonic Analysis, 3rd edn. Cambridge University Press, Cambridge (2004)
Kissin E., Shulman V.S.: Operator multipliers. Pac. J. Math. 227(1), 109–141 (2006)
Kissin E., Shulman V.S.: Classes of operator-smooth functions. I. Operator-Lipschitz functions. Proc. Edinb. Math. Soc. (2) 48(1), 151–173 (2005)
Kissin E., Shulman V.S.: On the range inclusion of normal derivations: variations on a theme by Johnson, Williams and Fong. Proc. Lond. Math. Soc. (3) 83(1), 176–198 (2001)
Lahiri B.K.: On translations of sets in topological groups. J. Indian Math. Soc. (N.S.) 39, 173–180 (1975)
Mattila P.: Geometry of Sets and Measures in Euclidean Spaces. Fractals and Rectifiability. Cambridge University Press, Cambridge (1995)
Peller V.: Hankel operators in the theory of perturbations of unitary and selfadjoint operators (Russian). Funktsional. Anal. i Prilozhen. 19(2), 37–51 (1985) 96
Potapov, D., Sukochev, F.: Operator Lipschitz functions in Scahtten-von Neumann classes. Acta Math. (2010, to appear)
Shulman V.S., Turowska L.: Operator synthesis I: synthetic sets, bilattices and tensor algebras. J. Funct. Anal. 209, 293–331 (2004)
Shulman V.S., Turowska L.: Operator synthesis II: individual synthesis and linear operator equations. J. Reine Angew. Math. 590, 143–187 (2006)
Spronk N., Turowska L.: Spectral synthesis and operator synthesis for compact groups. J. Lond. Math. Soc. (2) 66, 361–376 (2002)
Rudin W.: Fourier Analysis on Groups. Wiley, New York (1990)
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I. G. Todorov was supported by EPSRC grant D050677/1. L. Turowska was supported by the Swedish Research Council.
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Shulman, V.S., Todorov, I.G. & Turowska, L. Closable Multipliers. Integr. Equ. Oper. Theory 69, 29–62 (2011). https://doi.org/10.1007/s00020-010-1819-2
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DOI: https://doi.org/10.1007/s00020-010-1819-2