Closed Superstring Amplitudes, Single-Valued Multiple Zeta Values and Deligne Associator

Understand

We revisit the tree-level closed superstring amplitude and identify its alpha'-expansion as series with single-valued multiple zeta values as coefficients.

• The latter represent a subclass of multiple zeta values originating from single-valued multiple polylogarithms at unity.
• Moreover, the alpha'-expansion of the closed superstring amplitude can be cast into the same algebraic form as the open superstring amplitude: the closed superstring amplitude essentially is the single-valued version of the open superstring amplitude.
• This fact points into a deeper connection between gauge and gravity amplitudes than what is implied by Kawai-Lewellen-Tye relations.