We analyze the free ambitwistor string field theory action for the bosonic string, heterotic string and both GSO sectors of the Type II string. The spectrum contains nonunitary states and provides an interesting consistency test for one-loop ambitwistor string computations.

Constructing a consistent four-dimensional Lagrangian for charged massive higher-spin fields propagating in an electromagnetic background is an open problem. In 1989, Argyres and Nappi used bosonic open string field theory to construct a Lagrangian for charged massive spin-2 fields in a constant electromagnetic background. In this paper, we use the four-dimensional hybrid formalism for open superstring field theory to construct a supersymmetric Lagrangian for charged massive spin-2 and spin-3/2 fields in a constant electromagnetic background. The hybrid formalism has the advantage over the RNS formalism of manifest $$ \mathcal{N} $$ N = 1 d=4 spacetime supersymmetry so that the spin-2 and spin-3/2 fields are combined into a single superfield and there is no need for picture-changing or spin fields.

In this work, we investigate the bosonic chiral string in the sectorized interpretation, computing its spectrum, kinetic action and 3-point amplitudes. As expected, the bosonic ambitwistor string is recovered in the tensionless limit.We also consider an extension of the bosonic model with current algebras. In that case, we compute the effective action and show that it is essentially the same as the action of the mass-deformed (DF ) 2 theory found by Johansson and Nohle. Aspects which might seem somewhat contrived in the original construction -such as the inclusion of a scalar transforming in some real representation of the gauge group -are shown to follow very naturally from the worldsheet formulation of the theory. *

We analyse the BRST cohomology of the Ramond sector of heterotic ambitwistor theory. We also write the free string field theory action and compute the supersymmetry transformations.

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