Exploratory Fits of an Effective Logarithmic Potential to Selected SPARC Rotation Curves

This work investigates a minimal effective logarithmic-potential correction as a phenomenological diagnostic for galaxy rotation curves. The model introduces an effective velocity-squared contribution of the form A r / (r + r0) which approaches a constant asymptotic correction at large radius. Using selected SPARC rotation-curve data, the study evaluates whether this two-parameter effective ansatz can reproduce flat-rotation-curve-like behavior and reduce residuals relative to baryonic-only baselines. The analysis includes representative-galaxy fits, bootstrap uncertainty estimates, broader-sample robustness tests, and diagnostic comparisons with simple MOND and NFW variants. The purpose of this work is not to replace dark matter, MOND, or ΛCDM. Instead, the effective logarithmic-potential model is presented as a restricted phenomenological diagnostic framework for exploring rotation-curve behavior. This manuscript is released as a research preprint.