The Hadronic Light-by-Light Contribution to the Muon Anomalous Magnetic Moment: Where do we stand?
We review the status of the hadronic light-by-light contribution to the muon anomalous magnetic moment and critically compare recent calculations. We also study in detail which momentum regions the pi0 exchange main contribution originates. We also argue that amu{light-by-light} = (11 pm 4) times 10-10 encompasses the present understanding of this contribution and comment on some directions to imp