Motivic Superstring Amplitudes

I review the recent advances in open superstring N-point tree-level computations. One basic ingredient is a basis of (N-3)! generalized Gaussian hypergeometric functions encoding all string effects through their dependence on the string tension alpha’.
The structure of the open superstring amplitudes is analyzed. We find a striking and elegant form, which allows to disentangle its alpha’-expansion into several contributions accounting for different classes of multiple zeta values. This form is bolstered by the decomposition of motivic multiple zeta values, i.e. the latter encapsulate the alpha’-expansion of the superstring amplitude.
Moreover, a morphism induced by the coproduct maps the alpha’-expansion onto a non-commutative Hopf algebra. This map represents a generalization of the symbol of a transcendental function. In terms of elements of this Hopf algebra the alpha’-expansion assumes a very simple and symmetric form, which carries all the relevant information.