If the photon had a nonzero mass (mγ=0), the Coulomb potential would be replaced by the Yukawa potential,
V(r)=−4πϵ0e2re−μr,(8.73)
where μ=mγc/ℏ. With a trial wave function of your own devising, estimate the binding energy of a "hydrogen" atom with this potential. Assume μa≪1, and give your answer correct to order (μa)2.