Massive strings from a haunted field theory

In this work we present the $α'$-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 worldsheet 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 worldsheet correlators in conventional bosonic strings (with arbitrary number of massless and mass level one states), and outline a new perspective on massive resonances in string theory.