Spiky strings on NS5-branes

We study rigidly rotating strings in the near-horizon geometry of a stack of Neveu-Schwarz (NS) 5-branes. We solve the Nambu-Goto action of the fundamental string in the presence of a NS-NS two form (Bμν) and find out limiting cases corresponding to magnon and spike like solutions.     

Beijing Lectures on the Grade Restriction Rule

The authors describe the relationships between categories of B-branes in different phases of the non-Abelian gauged linear sigma model.The relationship is described explicitly for the model proposed by Hori and Tong with non-Abelian gauge group that connects two non-birational Calabi-Yau varieties studied by Rφdland.A grade restriction rule for this model is derived using the hemisphere partition function and it is used to map B-type D-branes between the two Calabi-Yau varieties.     

Standard model on D-branes

I briefly outline previous work on getting the (supersymmetric) standard model from string theory, and then describe two ecent attempts using D-branes. The first uses D3-and D7-branes and gives a supersymmetric standard model with extra vector-like matter and an intermediate unification scale. The second uses intersecting D4-branes and yields a non-supersymmetric spectrum with TeV-scale unification.     

Universal soft terms in the MSSM on D-branes

In Type II string vacua constructed from intersecting/magnetized D-branes, the supersymmetry-breaking soft terms are genericaly non-universal. It is shown that universal supersymmetry-breaking soft terms may arise in a realistic MSSM constructed from intersecting/magnetized D-branes in Type II string theory. For the case of dilaton-dominated supersymmetry breaking, it is shown that the universal scalar mass and trilinear coupling are fixed such that _m0=(1/2)_m3/2$m_0=(1/2)m_{3/2}$ and _A0=−_m1/2$A_0=-m_{1/2}$. In addition, soft terms where the universal scalar mass _m0$m_0$ is much larger than the universal gaugino mass _m1/2$m_{1/2}$ may be easily obtained within the model. Finally, it is shown that the special dilaton and no-scale strict moduli boundary conditions, which are well known in heterotic string constructions, may also be obtained.     

p-Wave superconductors in D-brane systems

In this work we take the intersecting D-brane models to explore some properties of p-wave superconductor at strong coupling. Our studies are focused on four-dimensional spacetime, which is not completely researched as in planar case. Optimistically, the AdS/CFT approach to superconductor, or more precisely superconducting-like phase transition, can give us some intuitions about mysterious high _Tc$T_c$ superconductors. Concretely, we use defect D4/D6 and D4/D4 (noncritical) models to carry out comparative investigations. To make the system in the finite temperature bath, we assume that the superconducting phase is in the deconfined and chiral symmetry restoring phase for black D4-brane geometry. For the background fields, we use both analytical and numerical methods to solve the coupled nonlinear equations of motion. Near the phase transition, both methods give the mean filed behavior for the superconducting condensate. We then study gauge field perturbations of the systems to probe the AC conductivity. Similar to previous results, there comes out a gap in low frequency regime and the conductivity gets exponentially small as the condensation is enhanced. In contrast to previous investigations, we also compute the AC conductivity along the x direction, which needs to study a coupled sets of fluctuation modes. This shows us the anisotropic feature of p-wave superconductors.