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Conformal and Einstein gravity from twistor actions, Class.Quant.Grav
"... Abstract: We use the embedding of Einstein gravity with cosmological constant into conformal gravity as a basis for using the twistor action for conformal gravity to obtain MHV scattering amplitudes not just for conformal gravity, but also for Einstein gravity on backgrounds with nonzero cosmologic ..."
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Abstract: We use the embedding of Einstein gravity with cosmological constant into conformal gravity as a basis for using the twistor action for conformal gravity to obtain MHV scattering amplitudes not just for conformal gravity, but also for Einstein gravity on backgrounds with nonzero cosmological constant. The new formulae for the gravitational MHV amplitude with cosmological constant arise by summing Feynman diagrams using the matrixtree theorem. We show that this formula is welldefined (i.e., is independent of certain gauge choices) and that it nontrivially reproduces Hodges ’ formula for the MHV amplitude in the flatspace limit. We give a preliminary discussion of an MHV formalism for more general amplitudes obtained from the conformal gravity twistor action in an axial gauge. We also see that the embedding of Einstein data into the conformal gravity action can be performed offshell in twistor space to give a proposal for an Einstein twistor action that automatically gives the same MHV amplitude. These ideas extend naturally to N = 4 supersymmetry. ar X iv
Worldsheet factorization for twistorstrings
"... Abstract: We study the multiparticle factorization properties of two worldsheet theories which–at treelevel–describe the scattering of massless particles in four dimensions: the BerkovitsWitten twistorstring for N = 4 superYangMills coupled to N = 4 conformal supergravity, and the Skinner twist ..."
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Abstract: We study the multiparticle factorization properties of two worldsheet theories which–at treelevel–describe the scattering of massless particles in four dimensions: the BerkovitsWitten twistorstring for N = 4 superYangMills coupled to N = 4 conformal supergravity, and the Skinner twistorstring for N = 8 supergravity. By considering these stringlike theories, we can study factorization at the level of the worldsheet before any Wick contractions or integrals have been performed; this is much simpler than considering the factorization properties of the amplitudes themselves. In Skinner’s twistorstring this entails the addition of worldsheet gravity as well as a formalism that represents all external states in a manifestly symmetric way, which we develop explicitly at genus zero. We confirm that the scattering amplitudes of Skinner’s theory, as well as the gauge theory amplitudes for the planar sector of the BerkovitsWitten theory, factorize appropriately at genus zero. In the nonplanar sector, we find behavior indicative of conformal gravity in the BerkovitsWitten twistorstring. We contrast factorization in twistorstrings with the story in ordinary string theory, and also make some remarks on higher genus factorization and disconnected prescriptions. ar X iv
Twistor/ambitwistor strings and nullsuperstrings in spacetime
 of D = 4, 10 and 11 dimensions, ArXiV:1404.1299 [hepth
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