Axial repulsion of pusher stresslets (${\ell }^3={\ell }_0^3+3St/(2\pi \mu )$)

Two equal parallel axial point stresslets with positive strength $S$ and separation $\ell$ have relative velocity $S/(2\pi \mu {\ell }^2)$. Identical self-propulsion cancels in their relative motion. The solution is the displayed cubic separation law while the far-field approximation is valid.