Co-Authors: Yu-tin Huang (National Taiwan University), Congkao Wen (Tor Vergata Rome)


In this talk based on arXiv:1602.01674, we provide evidence for universality in the low-energy expansion of tree-level string interactions. More precisely, in the α ′
α′
-expansion of tree-level scattering amplitudes, we conjecture that the leading transcendental coefficient at each order in α ′
α′
is universal for all perturbative string theories. We have checked this universality up to seven points and trace its origin to the ability to restructure the disk integrals of open bosonic string into those of the superstring. The accompanying kinematic functions have the same low-energy limit and do not introduce any transcendental numbers in their α ′
α′
-corrections. Universality in the closed-string sector then follows from the Kawai-Lewellen-Tye-relations.