# Finite dimensional approximations for Nica-Pimsner algebras

## TL;DR

This paper establishes necessary and sufficient conditions for the nuclearity of Nica-Pimsner algebras associated with various quasi-lattice ordered groups, expanding understanding of their structure and properties.

## Contribution

It provides a comprehensive analysis of nuclearity conditions for Nica-Pimsner algebras over quasi-lattices, including new results for product systems and classes like Baumslag-Solitar and right-angled Artin groups.

## Key findings

- Characterization of nuclearity for free abelian lattice cases.
- Extension of results to product systems over quasi-lattices.
- Analysis of exactness and conditions for faithful conditional expectations.

## Abstract

We give necessary and sufficient conditions for nuclearity of Cuntz-Nica-Pimsner algebras for a variety of quasi-lattice ordered groups. First we deal with the free abelian lattice case. We use this as a stepping stone to tackle product systems over quasi-lattices that are controlled by the free abelian lattice and satisfy a minimality property. Our setting accommodates examples like the Baumslag-Solitar lattice for $n=m>0$ and the right-angled Artin groups. More generally the class of quasi-lattices for which our results apply is closed under taking semi-direct and graph products. In the process we accomplish more. Our arguments tackle Nica-Pimsner algebras that admit a faithful conditional expectation on a small fixed point algebra and a faithful copy of the co-efficient algebra. This is the case for CNP-relative quotients in-between the Toeplitz-Nica-Pimsner algebra and the Cuntz-Nica-Pimsner algebra. We complete this study with the relevant results on exactness.