The Matrix String Theory, i.e. the two dimensional U(N) SYM with N = (8, 8)
supersymmetry, has classical BPS solutions that interpolate between an initial and a final
string configuration via a bordered Riemann surface. The Matrix String Theory amplitudes
around such a classical BPS background, in the strong Yang–Mills coupling, are therefore
candidates to be interpreted in a stringy way as the transition amplitude between given
initial and final string configurations. In this paper we calculate these amplitudes and
show that the leading contribution is proportional to the factor g−χ, where χ is the Euler s
characteristic of the interpolating Riemann surface and gs is the string coupling. This is the factor one expects from perturbative string interaction theory.
