A Tail-Dominated High-Velocity Excess in Wide-Binary Kinematics

Using the Gaia eDR3 wide-binary catalog, we perform a conservative, data-driven analysis designed to isolate robust kinematic structure under stringent contamination and quality controls. We construct a dimensionless velocity statistic R = v_rel/V_c,N and focus on high-quantile diagnostics to probe the behavior of the velocity distribution tail. Across all samples, we find that the median remains smooth and close to Newtonian expectations, while the high-velocity tail exhibits a robust excess. The signal is therefore not a bulk deviation, but a tail-dominated effect. When expressed as a function of projected separation, the signal appears non-monotonic and ambiguous. Recasting the analysis in terms of the internal acceleration parameter $g_int/a_QV provides a physically motivated coordinate in which the tail behavior is more clearly organized. However, a permutation test does not establish statistically significant non-monotonic structure in acceleration space, indicating the detailed shape of the signal is not resolved at the present sample size. To isolate the deviation from Newtonian expectations, we construct a tail-excess ratio and find a persistent enhancement of the high-velocity tail relative to the Newtonian baseline. A hierarchy of null tests demonstrates that this tail enhancement cannot be reproduced by projection effects, measurement uncertainties, or uniform contamination. While structured contamination from unresolved hierarchical systems remains a possible contributor, it does not naturally account for the observed behavior. We conclude that wide-binary kinematics exhibit a robust excess in the high-velocity tail relative to Newtonian expectations, providing a clean empirical benchmark for structure in the low-acceleration regime.