A new class of twistor string theories was recently constructed by Abou-Zeid, Hull, and Mason. The most interesting one of these theories has the particle content of $\mathcal{N}=8$ supergravity. Arguments are given for the vanishing of the ($+--$)-helicity amplitude for gravitons which suggest that this theory describes a chiral $\mathcal{N}=8$ supergravity rather than Einstein supergravity.

• Received 25 November 2007

DOI:https://doi.org/10.1103/PhysRevD.78.041501