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 (15[1])and is named after this scientist and Hellmann. To expand (15[1])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 (10[2])involves (10[1])introducing (10[1])a second variable (10[1])and differentiating to simplify the integrand. This scientist’s “diagram” uses arrows (10[1])and waves to describe the interactions of subatomic particles and draws photons as squiggly lines. For 10 points, name this American theoretical physicist. ■END■