  A covariant closed superstring field theory, equivalent to classical
ten-dimensional Type II supergravity, is presented. The defining conformal
field theory is the ambitwistor string worldsheet theory of Mason and Skinner.
This theory is known to reproduce the scattering amplitudes of Cachazo, He and
Yuan in which the scattering equations play an important role and the string
field theory naturally incorporates these results. We investigate the operator
formalism description of the ambitwsitor string and propose an action for the
string field theory of the bosonic and supersymmetric theories. The correct
linearised gauge symmetries and spacetime actions are explicitly reproduced and
evidence is given that the action is correct to all orders. The focus is on the
Neveu-Schwarz sector and the explicit description of tree level perturbation
theory about flat spacetime. Application of the string field theory to general
supergravity backgrounds and the inclusion of the Ramond sector are briefly
discussed.

High Energy Physics - Theory