This man is the alphabetically-former of a namesake technique that uses the angular orbital momentum number as a small parameter to find the mean value of one over r-squared. That technique relates the derivative of total energy to the mean value of the partial derivative of the Hamiltonian and is named after this scientist and Hellmann. To expand the time-evolution operator, a sum of constructs named after this scientist can be used to represent a (*) Dyson series. This scientist’s “trick” for single-variable integrals involves introducing a second variable (10[1])and differentiating to simplify the integrand. This scientist’s “diagram” uses arrows and waves to (10[1])describe the interactions of subatomic particles and draws photons as squiggly lines. For 10 points, name this American theoretical physicist. ■END■