A generalization of the Gell-Mann-Low theorem is applied to the
antimuon-electron system. The bound state spectrum is extracted numerically. As
a result, fine and hyperfine structure are reproduced correctly near the
nonrelativistic limit (and for arbitrary masses). We compare the spectrum for
the relativistic value alpha = 0.3 with corresponding calculations in
light-front quantization.Comment: 6 pages, LaTeX, 2 figures, uses aipxfm.sty. Talk delivered at the XI
Mexican Workshop on Particles and Fields, Tuxtla Gutierrez, Mexico, November
7-12, 2007; to be published in the proceeding