Bosonic construction of superstring theory and related topics

This thesis splits into two parts. In the first part we introduce a bosonic construction of the ten-dimensional fermionic theories. This construction relies on a consistent truncation procedure which can produce fermions out of bosons. We illustrate this truncation procedure in the case of type II superstring theories, which emerge as the truncation of the 26-dimensional closed bosonic string theory compacified on the weight lattice of E(_8) x E(_8). The same truncation procedure can be applied to the unoriented bosonic string theory compactified on the above lattice and produces the type I superstring theory with the Chan-Paton gauge group reduced from SO(2(^13)) to SO(32). We also demonstrate that the BPS D-branes in Type I theory can be obtained from the bosonic D-branes wrapping on the above lattice by using the technique of Boundary Conformal Field Theory. In the second part, we construct new four-dimensional configurations of oppositely charged static black hole pairs (diholes) which are solutions of the low-energy effective action of string theories. The black holes are extrernal and carry four different charges. We also generalize the dihole solution to a theory which has an arbitrary number of abelian gauge fields and scalars where the diholes are composite objects. We uplift the dihole solutions to higher dimensions in order to describe intersecting brane-anti-brane configurations in string theory. The properties of the strings and membranes stretched between the brane and anti-brane are discussed.