  In the first part of this dissertation, we study two different aspects of
string phenomenology. First we discuss the complementary signals of low mass
superstrings at the proposed electron-positron facilities (ILC and CLIC), in
e+e- and {\gamma} {\gamma} collisions. We examine all relevant four-particle
amplitudes evaluated at the center of mass energies near the mass of lightest
Regge excitations and extract the corresponding pole terms. Secondly, we
consider string realizations of the Randall-Sundrum effective theory and
explore the search for the lowest massive Regge excitation of the gluon and of
the extra (color singlet) gauge boson inherent of D-brane constructions. We
also study the ratio of dijet mass spectra at small and large scattering
angles. We show that with the first fb-1 such a ratio can probe lowest-lying
Regge states for masses ~3.0 TeV. Finally, we propose that the 3.2$\sigma$
excess at about $140 {\rm GeV}$ in the dijet mass spectrum of $W$ + jets
reproted by the CDF Collaboration originates in the decay of a leptophobic $Z'$
that can be related to the U(1) symmetries inherent of D-brane models. In the
remaining parts of this dissertation, we discuss several points that may help
to clarify some questions that remain about the anomaly puzzle in N=1
supersymmetric Yang-Mills theory and we investigate the issue that the Dirac
Hamiltonian of a spin-1/2 particle in a curved background appears to be
non-hermitian.
