Implication from strong convergence of (η^(k), b^(k)) to strong convergence of amalgamated free copies

Determine whether the following implication holds: if the pairs (η^(k), b^(k)) converge strongly in covariance law to (η, b), then the pairs (b^(k), S^(k)) converge strongly (i.e., operator norms of all noncommutative polynomials converge) to (b, S), where S^(k) is a tuple of freely independent copies, with amalgamation over M_{n(k)}, of the (M_{n(k)}, η^(k))-semicircular family X_free^(k), and S is a tuple of freely independent copies, with amalgamation over B, of the (B, η)-semicircular family X.

Background

The paper establishes strong convergence of Gaussian and deterministic matrix models to operator-valued semicircular families under an assumption that involves convergence of amalgamated free copies Sk of the (M_{n(k)}, ηk)-semicircular family together with bk. The authors note this is a natural hypothesis for their proof strategy, which compares Gaussian matrices to their operator-valued semicircular counterparts.

They remark that it would be more natural to assume strong convergence in covariance law of (ηk, bk) to (η, b). However, it is unknown in general whether this stronger-looking assumption implies the required strong convergence of the pairs (bk, Sk) to (b, S). For fixed base algebras, strong convergence is known to pass to free products (Skoufranis; Pisier), but the present setting involves varying base algebras and operator-valued covariance, for which this implication is not established.

References

While unfortunately we do not know whether strong convergence of $(\eta{(k)},b{(k)})$ to $(\eta,b)$ implies strong convergence of $(b{(k)},S{(k)})$ to $(b,S)$ in general, our hypotheses hold in many cases of interest, and there are several available techniques to compute or estimate operator norms for polynomials in semicirculars (see ).

Strong convergence to operator-valued semicirculars (2506.19940 - Jekel et al., 24 Jun 2025) in Introduction, discussion following Theorem A (Operator-valued strong convergence)