Massless vector pole of the Veneziano amplitude (${\mathrm{Res}}_{s=0}A=-(t+2)$)

The pole at $s=0$ has residue $-(t+2)=-(t-u)/2$ for unit-slope tachyons. It is proportional to conserved scalar-pair vector currents and linear in the scattering-angle cosine, exhibiting a massless spin-one intermediate string state.