The Supersymmetric Particle Spectrum in Orbifold Compactifications of String Theory

The supersymmetry breaking parameters and the resulting supersymmetric particle spectrum are studied in orbifold compactifications of string theory under the assumption that unification of gauge coupling constants at about $10^{16}$ GeV is a consequence of large moduli dependent string loop threshold corrections. The effect on the spectrum of various assumptions as to the modular weights of the states, the values of the Green-Schwarz parameter, $\delta_{GS}$, the origin of the $\mu$ parameter and the moduli dependence of Yukawa couplings is discussed. The effect of radiative corrections to the effective potential is also considered.