Fluid Space Theory without Superfluid Component: A Two-Parameter Phenomenological Model for Galaxy Rotation Curves and Its Comparison with ΛCDM and MOND under Strict Priors

This work presents a simplified two-parameter Fluid Space Theory (FST) by removing the long-range superfluid component, retaining only the coherent inflow term combined with baryonic Newtonian gravity. We perform a fair statistical comparison between the 2-parameter FST, cored NFW ΛCDM (3 free parameters with tight concentration-mass priors), and fixed-\(a_0\) MOND (zero free parameters) using the full SPARC sample of 175 disk galaxies. All models are fitted with identical differential evolution optimization settings under consistent error treatments. Key statistical outcomes: The mean Bayesian Information Criterion (BIC) of the simplified FST is 1001.99, slightly worse than ΛCDM (982.26) yet vastly superior to fixed MOND (4420.30). FST obtains the minimum BIC for 121 out of 175 galaxies (69.1%), while ΛCDM wins in 51 galaxies (29.1%) and MOND only in 3 galaxies (1.7%). The covariance matrix condition number of the two FST parameters equals 10.7, eliminating severe parameter degeneracy found in the original 4-parameter FST (B7 model). Removing the superfluid component lowers the average BIC by 5.85 without worsening the global \(\chi^2\) fit, proving the superfluid term is statistically unnecessary for SPARC rotation curve data. A universal fixed acceleration constant \(a_0\) fails drastically against SPARC observations, strongly disfavouring the standard MOND core assumption. We transparently report both average BIC and per-galaxy model preference counts to avoid one-sided conclusions. This archive provides a fully reproducible benchmark for fluid-based alternative gravity theories without dark matter.