Massive Strings from a Field Theory with Ghosts

In this Letter, we present the ${\alpha }^{\prime }$-exact background equations of motion of the bosonic chiral string (also known as Hohm-Siegel-Zwiebach model), with the spin-two ghost fields integrated out. This is the first instance of a world sheet model in which all corrections are fully determined in a generic curved spacetime. As a concrete cross-check, we find complete agreement between all three-point and a sample of four-point tree-level scattering amplitudes computed using field theory methods and the chiral string prescription. These equations of motion provide a field theoretical shortcut to compute world sheet correlators in conventional bosonic strings (with an arbitrary number of massless and mass-level-one states) and outline a new perspective on massive resonances in string theory.