Related papers: Singularities, Gauge Dynamics, and Nonperturbative…
We investigate the lifting of half-maximal four-dimensional gauged supergravities to compactifications of string theory. It is shown that a class of such supergravities can arise from compactifications of IIA string theory on manifolds of…
We consider the generation of a non-perturbative superpotential in F-theory compactifications with flux. We derive a necessary condition for the generation of such a superpotential in F-theory. For models with a single volume modulus, we…
I discuss the role of spacetime supersymmetry in the interplay between strong/weak coupling duality and target space duality in string theory which arises in string/string duality. This can be seen via the construction of string soliton…
The dynamics of superstring, supergravity and M theories and their compactifications are probed by studying the various perturbation theories that emerge in the strong and weak coupling limits for various directions in coupling constant…
We show that type I string theory compactified in four dimensions in the presence of constant internal magnetic fields possesses N=1 supersymmetric vacua, in which all Kahler class and complex structure closed string moduli are fixed.…
On compactification to six spacetime dimensions, the fundamental heterotic string admits as a soliton a dual string whose effective worldsheet action couples to the background fields of the dual formulation of six-dimensional supergravity.…
We investigate the global structure of the states becoming light at perturbative limits of 4d $\mathcal{N}=1$ string and M-theory compactifications, identifying the different duality frames that emerge asymptotically and how they fit…
In these lecture notes duality tests and instanton effects in supersymmetric vacua of string theory are discussed. A broad overview of BPS-saturated terms in the effective actions is first given. Their role in testing the consistency of…
We consider a conformal system of a string and a particle defined in D=10+2 space-time dimensions. The extra time-like dimension is a gauge artifact and can be eliminated by choosing a gauge in which the SO(10,1) Lorentz symmetry is…
We derive the nonperturbative effect in type 0B string theory, which is defined by taking the double scaling limit of a one-matrix model with a two-cut eigenvalue distribution. However, the string equation thus derived cannot determine the…
We discuss non-perturbative corrections to the gauge kinetic functions in a four-dimensional N=2 gauge theory realized with a system of D7/D3-branes in a compactification of type I' theory on T_4/Z_2 x Z_2. The non-perturbative…
We give necessary conditions for the existence of perturbative heterotic and common sector type II string warped compactifications preserving four and eight supersymmetries to four spacetime dimensions, respectively. In particular, we find…
We review the duality between heterotic and F--theory string vacua with N=1 space-time supersymmetry in eight, six and four dimensions. In particular, we discuss two chains of four-dimensional F--theory/heterotic dual string pairs, where…
Using D3/D(-1) brane set-up in type IIB string theory we introduce gauge-stringy instantons in N=2 U(N) supersymmetry theories with one matter multiplet in symmetric representation. In addition to the gauge and stringy moduli there exist…
We review the derivation and the basic properties of the perturbative prepotential in N=2 compactifications of the heterotic superstring. We discuss the structure of the perturbative monodromy group and the embedding of rigidly…
We propose a twistor--like formulation of N=1, D=3,4,6 and 10 null superstrings. The model possesses N=1 target space supersymmetry and n=D-2 local worldsheet supersymmetry, the latter replaces the kappa-symmetry of the conventional…
In this paper we analyze the structure of supersymmetric vacua in compactifications of the heterotic string on certain manifolds with SU(3) structure. We first study the effective theories obtained from compactifications on half-flat…
In this thesis we study compactifications of type II string theories and M-theory to four dimensions. We construct the four-dimensional N=2 supergravities that arise from compactifications of type IIA string theory and M-theory on manifolds…
We study the relation between stringy instantons and strong dynamics effects in type IIB toric quiver gauge theories. By exploiting the involutive property of Seiberg duality we relate the classical constraint on the moduli space of the…
We propose a novel string theory propagating in a non-commutative deformation of the four dimensional space T* T^2 whose scattering states correspond to superconformal theories in 5 dimensions and the scattering amplitudes compute…