Nadia S. Larsen

• Huben, Robert; Kaliszewski, S.; Larsen, Nadia S. & Quigg, Johnnie Currie (2024). GAUGE-INVARIANT UNIQUENESS THEOREMS FOR P-GRAPHS. Mathematica Scandinavica. ISSN 0025-5521. 130(1), s. 87–100. doi: 10.7146/math.scand.a-139786. Fulltekst i vitenarkiv Vis sammendrag

  We prove a version of the result in the title that makes use of maximal coactions in the context of discrete groups. Earlier Gauge-Invariant Uniqueness theorems for C∗-algebras associated to P-graphs and similar C∗-algebras exploited a property of coactions known as normality. In the present paper, the view point is that maximal coactions provide a more natural starting point to state and prove such uniqueness theorems. A byproduct of our approach consists of an abstract characterization of co-universal representations for a Fell bundle over a discrete group.

• Larsen, Nadia S. & Vdovina, Alina (2024). Higher-dimensional digraphs from cube complexes and their spectral theory. Groups, Geometry, and Dynamics. ISSN 1661-7207. 18(4), s. 1427–1467. doi: 10.4171/GGD/787. Fulltekst i vitenarkiv Vis sammendrag

  We define k-dimensional digraphs and initiate a study of their spectral theory. The k-dimensional digraphs can be viewed as generating graphs for small categories called k-graphs. Guided by geometric insight, we obtain several new series of k-graphs using cube complexes covered by Cartesian products of trees, for k≥2. These k-graphs can not be presented as virtual products and constitute novel models of such small categories. The constructions yield rank-k Cuntz–Krieger algebras for all k≥2. We introduce Ramanujan k-graphs satisfying optimal spectral gap property and show explicitly how to construct the underlying k-digraphs.

• Farsi, Carla; Landry, Therese; Larsen, Nadia S. & Packer, Judith (2024). Spectral triples for noncommutative solenoids and a Wiener’s lemma. Journal of Noncommutative Geometry. ISSN 1661-6952. 18(4), s. 1415–1452. doi: 10.4171/JNCG/557. Fulltekst i vitenarkiv Vis sammendrag

  In this paper, we construct odd finitely summable spectral triples based on length functions of bounded doubling on noncommutative solenoids. Our spectral triples induce a Leibniz Lip-norm on the state spaces of the noncommutative solenoids, giving them the structure of Leibniz quantum compact metric spaces. By applying methods of R. Floricel and A. Ghorbanpour, we also show that our odd spectral triples on noncommutative solenoids can be considered as inductive limits of spectral triples on rotation algebras. In the final section, we prove a noncommutative version of Wiener’s lemma and show that our odd spectral triples can be defined to have an associated smooth dense subalgebra which is stable under the holomorphic functional calculus, thus answering a question of B. Long and W. Wu. The construction of the smooth subalgebra also extends to the case of nilpotent discrete groups.

• Farsi, Carla; Larsen, Nadia S.; Packer, Judith A. & Thiem, Nathaniel (2024). SIMPLICITY OF *-ALGEBRAS OF NON-HAUSDORFF Z_2-MULTISPINAL GROUPOIDS. Pure and Applied Functional Analysis. ISSN 2189-3756. 9(6), s. 1609–1634. Fulltekst i vitenarkiv Vis sammendrag

  We study simplicity of C*-algebras arising from self-similar groups of Z2- multispinal type, a generalization of the Grigorchuk case whose simplicity was first proved by L. Clark, R. Exel, E. Pardo, C. Starling, and A. Sims in 2019, and we prove results generalizing theirs. Our first main result is a sufficient condition for simplicity of the Steinberg algebra satisfying conditions modeled on the behavior of the groupoid associated to the first Grigorchuk group. This closely resembles conditions found by B. Steinberg and N. Szak´acs. We then deduce the simplicity of the associated C*-algebra, which is our second main result. Results of similar type were considered by B. Steinberg and N. Szak´acs in 2021, and later by K. Yoshida, but their methods did not follow the original methods of the five authors.

Se alle arbeider i NVA

• Larsen, Nadia S. (2026). Kvanteberegning - et blikk i et nytt univers. Fulltekst i vitenarkiv
• Kvaal, Simen; Bergan, Snorre; Fredheim, Håkon Richard; Larsen, Nadia S. & Neshveyev, Sergey (2025). A mathematical approach to CC theory. Fulltekst i vitenarkiv Vis sammendrag

  In this talk, I will outline work being carried out in an interdisciplinary project with the Operator Algebra group at Department of Mathematics, UiO. We have done a complete reformulation of coupled-cluster methods from the point of view of the bivariational principle, which gives a more “geometric” view. We have formulated general strategies for a posteriori and a priori error estimation using a nonlinear inf-sup theorem. Several results and proofs are simplified compared to those found in the literature. We are able to place all the analyses presently in the literature in this framework, in particular the seminal works by Rohwedder—Schneider, and Hassan—Maday—Wang

• Larsen, Nadia S. (2025). An abstract approach to coupled cluster methods. Fulltekst i vitenarkiv
• Larsen, Nadia S. (2025). An abstract approach to coupled-cluster methods. Fulltekst i vitenarkiv
• Larsen, Nadia S. & Fuchs, Franz Georg (2024). Quantum information and computing within mathematics departments at UiO and SINTEF: current perspectives. Fulltekst i vitenarkiv
• Larsen, Nadia S. (2023). Nice error frames and canonical abstract error groups. Fulltekst i vitenarkiv

Se alle arbeider i NVA