A fundamental property of QCD is the presence of the chiral anomaly, which is the primary component of the $pi^0rightarrowgammagamma$ decay amplitude. Based on this anomaly and its small ($simeq$ 4.5%) chiral correction, a firm prediction of the $pi^
0$ lifetime can be used as a test of QCD at confinement scale energies. The interesting experimental and theoretical histories of the $pi^0$ meson are reviewed, from discovery to the present era. Experimental results are in agreement with the theoretical prediction, within the current ($simeq$ 3%) experimental error; however, they are not yet sufficiently precise to test the chiral corrected result, which is a firm QCD prediction and is known to $simeq$ 1% uncertainty. At this level there exist experimental inconsistencies, which require attention. Possible future work to improve the present precision is suggested.
Using the methods of effective field theory we examine long range effects in mixed electromagnetic-gravitational scattering. Recent calculations which have yielded differing results for such effects are examined and corrected. We consider various spi
n configurations of the scattered particles and find that universality with respect to spin-dependence is obtained in agreement with expectations.
We study the gravitational scattering of massive particles with and without spin in the effective theory of gravity at one loop level. Our focus is on long distance effects arising from nonanalytic components of the scattering amplitude and we show t
hat the spin-independent and the spin-dependent long range components exhibit a universal form. Both classical and quantum corrections are obtained, and the definition of a proper second order potential is discussed.
We analyze the electromagnetic scattering of massive particles with and without spin and, using the techniques of effective field theory, we isolate the leading long distance effects beyond one photon exchange, both classical and quantum mechanical.
Spin-independent and spin-dependent effects are isolated and shown to have a universal structure.
