Compact form for the relativistic ponderomotive Hamiltonian

The infinite series of functions present in the ponderomotive Hamiltonian are explicitly summed using Newberger's sum rule. The result is a compact and easily evaluated expression for the ponderomotive Hamiltonian. Application of the K-chi theorem yields the linear susceptibility of relativistic magnetized plasma in agreement with, but generalizing, the previous result of Weiss and Weitzner