Finite-anisotropy extension of the exact microscopic analysis

Extend the exact microscopic analysis of anomalous spin-current fluctuations from the folded XXZ chain, representing the strong-anisotropy limit, to the XXZ chain at finite anisotropy, where the exact spin–charge separation used in the folded-chain solution is no longer directly available.

Background

The paper derives an exact finite-time moment-generating function and its long-time M-Wright asymptotics for the folded XXZ chain at infinite temperature. The derivation depends crucially on mapping the folded chain to the one-dimensional t–0 model, whose exact spin–charge separation reduces the problem to static spin combinatorics and free-fermion charge dynamics. The authors explicitly identify extending this analysis to finite anisotropy as an unresolved direction because that separation is not directly available for the finite-anisotropy XXZ chain.