This series consists of talks in the area of Superstring Theory.
I'll discuss a reformulation of twistor-string theory as a heterotic string. This clarifies why conformal supergravity arises and provides a link between the Berkovits and Witten pictures. The talk is based on
arXiv:0708:2276 with Lionel Mason.
I will discuss a solution generating technique that allows to generate
stationary axisymmetric solutions of five-dimensional gravity, starting
from static ones. This technique can be used to add angular momentum
to static configurations. It can also be used to add KK-monopole charge
to asymptotically flat five-dimensional solutions, thus generating geometries
that interpolate between five-dimensional and four-dimensional solutions.
To realize massive pions, I propose a variation of the holographic model of massless QCD using the D4/D8/D8bar-brane configuration proposed by Sakai and Sugimoto. The deformation breaks the chiral symmetry explicitly and I compute the mass of the pions and vector mesons. The observed value of the pion mass can be obtained. I also argue a chiral perturbation corresponding to the deformation.
We discuss D-brane instantons in four-dimensional string compactifications with special emphasis on Eucliden D2-branes in Type IIA orientifolds with spacetime filling D6-branes. These can induce superpotential couplings among the open string fields which are forbidden at the perturbative level since they violate some of the global U(1) symmetries generically present in string theory.