Characterizing Kadison--Schwarz maps on $M_3$

Abstract: Kadison--Schwarz (KS) maps form a natural class of positive linear maps lying between positivity and complete positivity. Despite their relevance in quantum dynamics and operator algebras, a detailed characterization of KS maps beyond low dimensions remains largely open. In this work we analyze unital linear maps on $M_3$ using the Bloch--Gell--Mann representation. Exploiting unitary equivalence and structural properties of the $\mathfrak{su}(3)$ algebra, we derive analytic conditions ensuring the Kadison--Schwarz property. Our approach clarifies the relation between KS maps and completely positive maps on $M_3$.