Speaker
Description
Tree-level string amplitudes may be fixed by a remarkably small set of consistency conditions. I will discuss bootstrap approaches to open and closed strings in four dimensions, focusing on planar N=4 super-Yang-Mills theory and N=8 supergravity deformed by higher-derivative operators. In both cases, we impose parity invariance on selected six-scalar amplitudes. We combine this condition with maximal supersymmetry, R-symmetry, tree-level factorization through six points, and positivity. For planar N=4 super-Yang-Mills theory with SU(4) R-symmetry, the resulting bounds converge to the Veneziano amplitude, providing strong evidence for uniqueness. For supergravity with SU(4)xSU(4) R-symmetry, the allowed region develops two sharp corners corresponding to the Virasoro-Shapiro amplitude and an infinite-spin-tower amplitude. Requiring finite spin content at the lowest massive level excludes the latter. Assuming the observed nonlinear relations persist to all orders, the Virasoro-Shapiro amplitude is then the unique solution.