Poblaguev arXiv Comment Identifies Methodological Artifacts in Rathmann HJET Depolarization Analysis

The comment dissects four core flaws in the 2026 Phys. Rev. Accel. Beams paper by Rathmann et al.: an artificial photon emission threshold, erroneous application of Fermi's Golden Rule to coherent hyperfine transitions, misinterpretation of power broadening as physical linewidth growth, and inconsistent spatial magnetic field handling. Each assumption produces non-physical depolarization rates that vanish under a unitary quantum evolution. Poblaguev replaces the rate-equation framework with direct integration of the time-dependent Schrödinger equation for the atomic hyperfine states in the passing beam's transient fields.

The corrected calculation demonstrates depolarization probabilities remain below 10^-5 per passage for EIC beam parameters, preserving the HJET target's utility for absolute polarimetry at the 0.5% precision target. This aligns with prior RHIC HJET operations where no beam-induced loss was observed above statistical limits. The critique highlights how semiclassical approximations break down when coherence times exceed the interaction duration.

Independent verification would require a full density-matrix simulation benchmarked against existing storage-ring data and a dedicated EIC beam test measuring target polarization retention versus bunch intensity. Until then, the Schrödinger-based bound supplies the more reliable limit for polarimeter design.