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Two-loop corrections to the orthopositronium and parapositronium decay rates due to vacuum polarization
We have calculated all O(a2) corrections to the orthopositronium and parapositronium decay rates due to vacuum polarization graphs. These contributions are independent of gauge and bound state formalism. Our results are +0.964960(4) (a/[pi])2 for orthopositronium and +0.4473430(6) (a/[pi])2 for psrapositronium relative to the lowest order rates We. also have an improved result for the one-loop one-photon-annihilation orthopositronium decay graph of -0.814 0574(10) (a/[pi]) times the lowest order rate.