S-duality Improved Superstring Perturbation Theory

Understand

Strong - weak coupling duality in string theory allows us to compute physical quantities both at the weak coupling end and at the strong coupling end.

• Furthermore perturbative string theory can be used to compute corrections to the leading order formula at both ends.
• We explore the possibility of constructing a smooth interpolating formula that agrees with the perturbation expansion at both ends and leads to a fairly accurate determination of the quantity in consideration over the entire range of the coupling constant.
• We apply this to study the mass of the stable non-BPS state in SO(32) heterotic / type I string theory with encouraging results.