The Tadpole Graph in Perturbative Open String Field Theory
Albin James (University of Southern California)
We study the one-loop tadpole in OSFT using the Moyal representation for the star product. Although the full integrand is badly divergent due to the closed string tachyon, it is expected from Boundary Conformal Field Theory to contain subleading terms that encode the effects of the Shapiro-Thorn closed string states. The analytic structure of the integrands, as a function of the Schwinger parameter in the Moyal formalism, shows that these allow for an asymptotic expansion for obtaining these subleading terms. A few coefficients for pure ghost external states would be presented.