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The main objects under study are quotients of multiplier algebras of certain complete Nevanlinna–Pick spaces, examples of which include the Drury–Arveson space on the ball and the Dirichlet space on the disc. We are particularly interested in the non-commutative Choquet boundaries for these quotients. Arveson’s notion of hyperrigidity is shown to be detectable through the essential normality of some natural multiplication operators, thus extending previously known results on the Arveson–Douglas conjecture. We also highlight how the non-commutative Choquet boundaries of these quotients are intertwined with their Gelfand transforms being completely isometric. Finally, we isolate analytic and topological conditions on the so-called supports of the underlying ideals that clarify the nature of the non-commutative Choquet boundaries.

The main objects of study in this paper are those functionals that are analytic in the sense that they annihilate the non-commutative disc algebra. In the classical univariate case, a theorem of F. and M. Riesz implies that such functionals must be given as integration against an absolutely continuous measure on the circle. We develop generalizations of this result to the multivariate non-commutative setting, upon reinterpreting the classical result. In one direction, we show that the GNS representation naturally associated to an analytic functional on the Cuntz algebra cannot have any singular summand. Following a different interpretation, we seek weak-$*$ continuous extensions of analytic functionals on the free disc operator system. In contrast with the classical setting, such extensions do not always exist, and we identify the obstruction precisely in terms of the so-called universal structure projection. We also apply our ideas to commutative algebras of multipliers on some complete Nevanlinna--Pick function spaces., 25 pages

We study similarity classes of commuting row contractions annihilated by what we call higher order vanishing ideals of interpolating sequences. Our main result exhibits a Jordan-type direct sum decomposition for these row contractions. We illustrate how the family of ideals to which our theorem applies is very rich, especially in several variables. We also give two applications of the main result. First, we obtain a purely operator theoretic characterization of interpolating sequences. Second, we classify certain classes of cyclic commuting row contractions up to quasi-similarity in terms of their annihilating ideals. This refines some of our recent work on the topic. We show how this classification is sharp: in general quasi-similarity cannot be improved to similarity. The obstruction to doing so is the existence, or lack thereof, of norm-controlled similarities between commuting tuples of nilpotent matrices, and we investigate this question in detail., 47 pages

Let $$\mathbb {V}$$ denote an n-tuple of shifts of finite multiplicity, and denote by $${{\mathrm{Ann}}}(\mathbb {V})$$ the ideal consisting of polynomials p in n complex variables such that $$p(\mathbb {V})=0$$ . If $$\mathbb {W}$$ on $$\mathfrak {K}$$ is another n-tuple of shifts of finite multiplicity, and there is a $$\mathbb {W}$$ -invariant subspace $$\mathfrak {K}'$$ of finite codimension in $$\mathfrak {K}$$ so that $$\mathbb {W}|\mathfrak {K}'$$ is similar to $$\mathbb {V}$$ , then we write $$\mathbb {V}\lesssim \mathbb {W}$$ . If $$\mathbb {W}\lesssim \mathbb {V}$$ as well, then we write $$\mathbb {W}\approx \mathbb {V}$$ . In the case that $${{\mathrm{Ann}}}(\mathbb {V})$$ is a prime ideal we show that the equivalence class of $$\mathbb {V}$$ is determined by $${{\mathrm{Ann}}}(\mathbb {V})$$ and a positive integer k. More generally, the equivalence class of $$\mathbb {V}$$ is determined by $${{\mathrm{Ann}}}(\mathbb {V})$$ and an m-tuple of positive integers, where m is the number of irreducible components of the zero set of $${{\mathrm{Ann}}}(\mathbb {V})$$ .

It is known that pure row contractions with one-dimensional defect spaces can be classified up to unitary equivalence by compressions of the standard $d$-shift acting on the full Fock space. Upon settling for a softer relation than unitary equivalence, we relax the defect condition and simply require the row contraction to admit a cyclic vector. We show that cyclic pure row contractions can be "transformed" (in a precise technical sense) into compressions of the standard $d$-shift. Cyclic decompositions of the underlying Hilbert spaces are the natural tool to extend this fact to higher multiplicities. We show that such decompositions face multivariate obstacles of an algebraic nature. Nevertheless, some decompositions are obtained for nilpotent commuting row contractions by analyzing function theoretic rigidity properties of their invariant subspaces., Comment: 31 pages

We extend some of the results of Agler, Knese, and McCarthy [1] to $n$-tuples of commuting isometries for $n>2$. Let $\mathbb{V}=(V_1,\dots,V_n)$ be an $n$-tuple of a commuting isometries on a Hilbert space and let Ann$(\mathbb{V})$ denote the set of all $n$-variable polynomials $p$ such that $p(\mathbb{V})=0$. When Ann$(\mathbb{V})$ defines an affine algebraic variety of dimension 1 and $\mathbb{V}$ is completely non-unitary, we show that $\mathbb{V}$ decomposes as a direct sum of $n$-tuples $\mathbb{W}=(W_1,\dots,W_n)$ with the property that, for each $i=1,\dots,n$, $W_i$ is either a shift or a scalar multiple of the identity. If $\mathbb{V}$ is a cyclic $n$-tuple of commuting shifts, then we show that $\mathbb{V}$ is determined by Ann$(\mathbb{V})$ up to near unitary equivalence, as defined in [1]., 29 pages. Ver. 2 : Fixed typos, added acknowledgements, removed some examples, fixed Lemma 7.13 (now 7.12)

The collection $\frk{C}_3$ of all triples of commuting contractions forms a family in the sense of Agler, and so has an "optimal" model $\pd\frk{C}_3$ generated by its extremal elements. A given $T\in\frk{C}_3$ is extremal if every $X\in\frk{C}_3$ extending $T$ is an extension by direct sum. We show that many of the known examples of triples in $\frk{C}_3$ that fail to have coisometric extensions are in fact extremal., Comment: 10 pages, pre-publication version, published in Operators and Matrices

Using a Krein indefinite metric in Fock space, the Hamiltonian for cut-off models of canonically quantized Higgs-Yang-Mills fields interpolating between the Gupta-Bleuler-Feynman and Landau gauges is shown to be essentially maximal accretive and essentially Krein selfadjoint.