Recently, it has been shown that if we consider the higher derivative correction, the viscosity bound conjectured to be η/s = 1/4π is violated and so is the causality. In this paper, we consider medium effect and the higher derivative correction simultaneously by adding charge and Gauss-Bonnet terms. We find that the viscosity bound violation is not changed by the charge. However, we find that two effects together create another instability for large momentum regime. We argue the presence of tachyonic modes and show it numerically. The stability of the black brane requires the Gauss-Bonnet coupling constant λ(= 2α ′ /l 2 ) to be smaller than 1/24. We draw a phase diagram relevant to the instability in charge-coupling space.

We study another realization of the Kerr/CFT correspondence. By imposing new asymptotic conditions for the near horizon geometry of Kerr black hole, an asymptotic symmetry which contains all of the exact isometries can be obtained. In particular, the Virasoro algebra can be realized as an enhancement of SL(2, R) symmetry of the AdS geometry. By using this asymptotic symmetry, we discuss finite temperature effects and show the correspondence concretely. † ymatsuo@apctp.org ‡ tsukioka@apctp.org § c m yoo@apctp.org

We investigate the generalized gauge theory which has been proposed previously and show that in two dimensions the instanton gauge fixing of the generalized topological Yang-Mills action leads to a twisted N = 2 supersymmetric action. We have found that the R-symmetry of N = 2 supersymmetry can be identified with the flavour symmetry of Dirac-Kähler fermion formulation. Thus the procedure of twist allows topological ghost fields to be interpreted as the Dirac-Kähler matter fermions.

At the dawn of a new theoretical tool based on the AdS/CFT correspondence for nonperturbative aspects of quantum chromodynamics, we give an interim review on the new tool, holographic QCD, with some of its accomplishment. We try to give an A-to-Z picture of the holographic QCD, from string theory to a few selected top-down holographic QCD models with one or two physical applications in each model. We may not attempt to collect diverse results from various holographic QCD model studies.