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Abstract

Using the pure spinor formalism in part I [1] we compute the complete
tree-level amplitude of N massless open strings and find a striking simple and
compact form in terms of minimal building blocks: the full N-point amplitude is
expressed by a sum over (N-3)! Yang-Mills partial subamplitudes each
multiplying a multiple Gaussian hypergeometric function. While the former
capture the space-time kinematics of the amplitude the latter encode the string
effects. This result disguises a lot of structure linking aspects of gauge
amplitudes as color and kinematics with properties of generalized Euler
integrals. In this part II the structure of the multiple hypergeometric
functions is analyzed in detail: their relations to monodromy equations, their
minimal basis structure, and methods to determine their poles and
transcendentality properties are proposed. Finally, a Groebner basis analysis
provides independent sets of rational functions in the Euler integrals.