N=4 Superconformal Bootstrap

We implement the conformal bootstrap for N = 4 superconformal field theories in four dimensions. The consistency of the four-point function of the stress-energy tensor multiplet imposes significant upper bounds for the scaling dimensions of unprotected local operators as functions of the central charge of the theory. At the threshold of exclusion, a particular operator spectrum appears to be singled out by the bootstrap constraints. We conjecture that this extremal spectrum is that of N = 4 supersymmetric Yang-Mills theory at an S-duality invariant value of the complexified gauge coupling.