Analyticity Domain for Off-shell Five-point Superstring Loop Amplitudes

Abstract: In an earlier work arXiv:2009.0337, we showed that for arbitrary Feynman loop diagrams (with no massless internal propagators) in closed superstring field theory, a known domain can be analytically extended by simply adjoining convex combinations of points drawn from it. Such extension yielded 350 of the well-known 370 primitive tubes for 5-point functions. In this paper, we consider the remaining 20 primitive tubes. We show that different types of convex combinations cover different sections of these tubes. We use a specific algorithm to analytically obtain 129 types of convex combinations along with their region of validity. Then, we use numerical techniques to locate points from those tubes that are not covered by them. This does not rule out the possibility of the leftover points being represented as desirable convex combinations. Indeed we give ways to improve our algorithm indicating that the leftover points can be covered.