Haagerup tensor products and Schur multipliers

Abstract: In this paper we compare various classes of Schur multipliers: classical matrix Schur multipliers, discrete Schur multipliers, Schur multipliers with respect to measures and Schur multipliers with respect to spectral measures. The main result says that in the case of Schur multipliers with respect to measures and spectral measures such Schur multipliers coincide isometrically with the Haagerup tensor products of the corresponding $L^\infty$ spaces. We deduce this result from a well known analogue of it for discrete Schur multipliers.