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The subject of this thesis are ambitwistor string models that describe massive particles by gauging currents to implement a symmetry reduction. Because the amplitude formulae one obtains as correlators in these models are really reductions of the ones presented in [1, 2], the body of the thesis will open with a discussion of properties and features of the six-dimensional superamplitudes that the massive formulae will inherit. Two different instances of symmetry reduction in the ambitwistor string will be considered. The first is a massive version of the RNS ambitwistor string. This provides a derivation of massive amplitude formulae that have support on massive scattering equations such as the ones predicted by Dolan and Goddard [3] and Naculich [4], together with a solid understanding of mass assignment both to external and propagating particles. The second consists of four dimensional twistorial models that will be shown to have an alternative interpretation as theories of maps into the phase space of complexified massive particles. This representation is more suitable to describe supersymmetric theories, such as the Coulomb branch of N = 4 sYM. An interesting class of theories is presented, which is obtained by symmetry reduction along the R-symmetry generators. For supergravity, this produces CSS gauged supergravities in four dimensions. In these theories a novel instance of ‘massive’ double copy structure arises. |
