A major part of my thesis is devoted to explore

certain issues of CP and flavor violations in conjunction with

those of fermion masses and neutrino oscillations in the context

of supersymmetric grand unification. An attempt is made to present

a {\it unified description} of four phenomena: (i) fermion masses

and mixings, (ii) neutrino oscillations, (iii) CP non conservation

and (iv) flavor violations in both the quark and the lepton

sectors, in accord with observations, within a single predictive

framework based on supersymmetric SO(10) or an effective $G(224)$

symmetry.

Including standard model and supersymmetric contributions, it is

shown that the framework correctly accounts for $\Delta m_K,~

\Delta m_{B_d}, ~ S(B_d\to J/\psi K_s)$ {\it and } $\epsilon_K$.

While SUSY-contribution is small ($\lsim $ few%) for the first

three quantities, that to $\epsilon_K$ is found to be sizable

($\sim$ 20-25%) and negative relative to the standard model as

desired. The model predicts $S(B_d\to \phi K_s)$ to be in the

range +(0.65--0.73), close to the standard model prediction; it

yields $Re(\epsilon'/\epsilon)_{SUSY}\approx +(4-14)\times

10^{-4}$. The model also predicts that the electric dipole moments

of the neutron and the electron should be discovered with

improvements in current limits by factors of 10 to 100.

Assuming SUSY-messenger scale to be higher than the GUT scale, it

is found that post-GUT physics, which has commonly been neglected

in the literature, contributes significantly to CP and flavor

violating processes. Including such contributions, the model

predicts enhanced rates for $\mu\to e\gamma, ~\tau\to \mu\gamma$

and $\mu N\to e N$ which should be seen in forthcoming

experiments.

A comparison of two promising SO(10) models, one with hierarchical

fermion mass matrices (by Babu, Pati and Wilczek), and the other

with lop-sided mass matrices (by Albright and Barr) is done, as

regards their predictions regarding CP and flavor violations.

Crucial tests are noted which would sharply distinguish between

the models.

Envisaging string origin of the effective unification symmetry in

4D, the second part of my thesis will explore the issue of gauge

coupling unification at the string scale when supersymmetric

standard model and an extension is embedded in an effective G(224)

or $G(214)\equiv SU(2)L\times U(1){I_{3R}}\times SU(4)^c$

symmetry near the GUT scale.