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Clark theory in the Drury-Arveson space

We extend the basic elements of Clark's theory of rank-one perturbations of backward shifts, to row-contractive operators associated to de Branges-Rovnyak type spaces $\mathcal H(b)$ contractively contained in the Drury-Arveson space on the unit ball in $\mathbb C^d$. The Aleksandrov-Clark measures on the circle are replaced by a family of states on a certain noncommutative operator system, and the backward shift is replaced by a canonical solution to the Gleason problem in $\mathcal H(b)$. In addition we introduce the notion of a "quasi-extreme" multiplier of the Drury-Arveson space and use it to characterize those $\mathcal H(b)$ spaces that are invariant under multiplication by the coordinate functions.