Topics in String Duality, CP Violation, and Baryogenesis.

We have investigated spacetime duality transformations applied to various string theories. Closed bosonic string theory is self-dual. Other string theories are not, but have interesting dual theories. We find that duality relates certain known superstring theories, and in the case of open strings, leads to theories in which strings interact with large membrane-like objects. In the case of unoriented strings, the dual theory consists of oriented strings interacting with a dynamical boundary in spacetime. The remainder of this work is unrelated to strings. We consider fundamental CP-violation in extensions of the Standard Model as it is manifested in electric dipole moments of particles. We have calculated the contribution to the electric dipole moment of the neutron in minimal supersymmetric extensions of the Standard Model from a CP-violating three gluon operator. We describe a calculation that shows that the electric dipole moment of the electron in a two doublet extension of the Standard Model receives its largest contribution from certain two loop Feynman graphs. Finally, we discuss baryogenesis in the early universe and obtain bounds on neutrino masses by requiring that B-L-violating interactions, in concert with unsuppressed anomalous electroweak transitions, did not erase a primordial baryon asymetry, and thus be compatible with present observations and the theory of nucleosynthesis.