The spectral form of Koopman representations of the group of measurable functions with values in the circle

Abstract

We compute the spectral form of the Koopman representation induced by a natural boolean action of $L^0(\lambda, {\mathbb T})$ identified earlier by the authors. Our computation establishes the sharpness of the constraints on spectral forms of Koopman representations of $L^0(\lambda, {\mathbb T})$ previously found by the second author.