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On the null origin of the ambitwistor string

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The Cachazo-He-Yuan (CHY) formulas are a remarkable representation of tree-level massless scattering amplitudes. Similarly to the Twistor String formulas, the CHY formula presents amplitudes as an integrals over the moduli space of Riemann surfaces constrained to the solutions of a set of algebraic equations called the scattering equations. Contrary to the Twistor String formulas, they can be written in any dimension and for a variety of massless theories. The CHY formula and the scattering equations can be derived using a 2D chiral CFT called the Ambitwistor String. The Ambitwistor string possesses peculiar characteristics when viewed as a string theory. Its low energy effective action is the same as Type II closed strings but the appearance of the scattering equations suggests a high-energy limit a la Gross and Mende. Also, its genus one correlation functions are modular invariant but UV divergent, they correspond to 10D SUGRA amplitudes. In this talk I’ll talk about a program started with P. Tourkine in which the Ambitwistor String is interpreted as a gauge fixing of the tensionless limit of the classical action of string theory. These are known as null strings and have a long history in the literature. I’ll review the null string and its supersymmetric extensions and show how the Ambitwistor String can be obtained from a particular gauge fixing of the null string. In doing so, I’ll address the issue of possible inequivalent quantizations of the null string, compare it to the case of the usual string and shed some light on its relation to the Ambitwistor String.

This talk is part of the Quantum Fields and Strings Seminars series.

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