Entrainment in the Inner Crust: Effective Masses and the Mobile Superfluid Fraction

Entrainment, the dragging of superfluid neutrons by the crustal lattice, decides how much of the inner crust's neutron fluid is actually free to store angular momentum. This study assembles a layer-by-layer entrainment profile from published band-theory effective masses and computes the density-weighted average that enters glitch reservoir budgets. The neutron effective mass ratio rises from 1.1 just below neutron drip to a peak of 14.0 in the deep inner crust. The corresponding mobile fraction of the superfluid, averaged with moment-of-inertia weighting, is 0.14, so the effective reservoir requirement inferred from any pulsar's activity must be multiplied by 7.00 relative to its no-entrainment value. Applied to Vela, the profile average places the required reservoir between the crustal supply of a light star and that of a canonical star, which is why Vela's mass is the decisive unknown in the crust-only debate. This study is simulated and computed from stated assumptions; it is not a measurement.