Institute for Advanced Study
The last years have seen remarkable progress in understanding the scattering amplitudes of massless particles in arbitrary dimensions. They not only exhibit a simplicity completely obscured by the Feynman Diagram approach, but also a structure reminiscent of the worldsheet models describing string theory. After reviewing the key developments, I will discuss these underlying worldsheet models - so-called ambitwistor strings - and derive simple formulas for the one-loop integrands in gauge theory and gravity. The models manifest the BCJ colour-kinematics duality, and I will end my talk by deriving a compact representation for pure Yang-Mills BCJ numerators.