Effective interactions of the open bosonic string via field theory

A bstract We describe a method to extract an effective Lagrangian description for open bosonic strings, at zero transcendentality. The method relies on a particular formulation of its scattering amplitudes derived from color-kinematics duality. More precisely, starting from a ( DF ) 2 + YM quantum field theory, we integrate out all the massive degrees of freedom to generate an expansion in the inverse string tension α ′. We explicitly compute the Lagrangian terms through O ( α ′ 4 ), and target the sector of operators proportional to F 4 to all orders in α ′.