Spin spreading on null planes from electromagnetic decay

In this thesis, the formalism for doing quantum electrodynamics on null planes is reviewed. The generators of the Poincare Group are evaluated in terms of creation and annihilation operators for fermions, antifermions, and photons. A non-electromagnetic bound state of a fermion and antifermion is constructed so that the state has spin zero and is capable of decaying into two photons via the electromagnetic interaction. The expectation value of the Pauli-Lubanski invariant which includes terms coming from the electromagnetic interactions, is evaluated using the bound state. It is shown that for any reasonable choice of the bound-state wave function the expectation value does not vanish. This indicated a spread in the spin of the bound state when the electromagnetic interactions make it unstable