We construct mass deformed SU(N) L-BLG theory together with $U(M-N)_k$ Chern-Simons theory. This mass deformed L-BLG theory is a low energy world volume theory of a stack of $N$ number of M2-brane far away from $C^4/Z_k$ singularity. We carry out thi
s by defining a special scaling limit of the fields of this theory and simultaneously sending the Chern-Simons level to infinity.
We study the Wilson loops and defects in the three dimensional QFT from the D-branes in the AdS(4) x CP**3 geometry. We find out explicit D-brane configurations in the bulk which correspond to both straight and circular Wilson lines extended to the b
oundary of AdS(4). We analyze critically the role of boundary contributions to the D2-branes with various topology and to the fundamental string actions.
We study general rotating string solution in the AdS(4) X CP**3 background with a B_NS holonomy turned on over ${bf CP}^1$ $subset $ $ {bf CP}^3$. We find the giant magnon and single spike solutions for the string moving in this background correspond
ing to open spin chain. We calculate the corresponding dispersion relation among various conserved charges for both the cases. We further study the finite size effect on both the giant magnon and single spike solutions.
We study a giant magnon and a spike solution for the string rotating on AdS(4) X CP**3 geometry. We consider rigid rotating fundamental string in the SU(2) X SU(2) sector inside the CP**3 and find out the general form of all the conserved charges. We
find out the dispersion relation corresponding to both the known giant magnon and the new spike solutions. We further study the finite size correction in both cases.
We study the solutions for fundamental string rotating in a background generated by a 1+1 dimensional intersection of two orthogonal stacks of fivebranes in type IIB string theory. We show the existence of magnon like solutions for the string moving
simultaneously in the two spheres in this background and find the relevant dispersion relation among the various conserved charges.
We study solutions for the rotating strings on the sphere with a background NS-NS field and on the Anti-de-Sitter spacetime. We show the existence of magnon and single spike solutions on R$times$S$^2$ in the presence of constant magnetic field as two
limiting cases. We also study the solution for strings on AdS$_3times$ S$^3$ with Melvin deformation. The dispersion relations among various conserved charges are shown to receive finite corrections due to the deformation parameter. We further study the rotating string on AdS$_3 times$ S$^3$ geometry with two conserved angular momenta on S$^3$ and one spin along the AdS$_3$. We show that there exists two kinds of solutions: a circular string solution and a helical string. We find out the dispersion relation among various charges and give physical interpretation of these solutions.
