Sang-Jin Sin

We consider the ultralight pseudo Nambu-Goldstone boson appearing in the late-time cosmological phase tansition theories as a major dark matter candidate. Since it is almost massless, its nature is more wavelike than particlelike. We study quantum mechanically how they from a galactic halo. Three predictions are made: (i) the mass profile \ensuremath{\rho}\ensuremath{\sim}${\mathit{r}}^{\mathrm{\ensuremath{-}}1.6}$; (ii) there are ripplelike fine structures in the rotation curve; (iii) the rotat

We study AC electric (σ), thermoelectric (α), and thermal $$ \left(\overline{\kappa}\right) $$ conductivities in a holographic model, which is based on 3+1 dimensional Einstein-Maxwell-scalar action. There is momentum relaxation due to massless scalar fields linear to spatial coordinate. The model has three field theory parameters: temperature (T), chemical potential (μ), and effective impurity (β). At low frequencies, if β < μ, all three AC conductivities (σ, α, $$ \overline{\kappa} $$ ) exhibi

We study the non-linear propagation of radiation in N=4 SYM at zero and finite temperature using the refined radius/scale duality in AdS/CFT. We argue that a pulse radiation by a quark at the boundary should be described holographically by a “point like object” passing through the center of the AdS bulk. We find that at finite temperature, the radiation stalls at a distance of 1/πT with a natural geometric and holographic interpretation. Indeed, the stalling is the holographic analogue of the gr

We investigate the D3–D7 model at finite U(1)B-charge chemical potential. We point out that the D3–D7 model with only the black-hole embeddings does not have the low-temperature and low-chemical-potential region in the grand-canonical ensemble, hence it is incomplete. The incomplete-ness is also seen as the thermodynamic instability in the canonical ensemble. We propose to solve the incomplete-ness problem by introducing the Minkowski embeddings at the finite U(1)B-charge. A possible physical in

We consider the gravity dual of strongly coupled system at a Lifshitz-fixed point and finite temperature, which was constructed in a recent work arXiv:0909.0263. We construct an Abelian–Higgs model in that background and calculate condensation and conductivity using holographic techniques. We find that condensation happens and DC conductivity blows up when temperature turns below a critical value. We also study the zero temperature limit of strongly coupled system at the Lifshitz-fixed point.

In a scattering process, the final state is determined by an initial state and an S-matrix. We focus on two-particle scattering processes and consider the entanglement between these particles. For two types initial states, i.e., an unentangled state and an entangled one, we calculate perturbatively the change of entanglement entropy from the initial state to the final one. Then we show a few examples in a field theory and in quantum mechanics.

Liquid crystal (LC)-based lenses are promising for a wide range of applications from optical communications and signal processing to three-dimensional displays. Among a variety of the LC-based lenses, several classes including the Fresnel type and the lenticular type are comprehensively reviewed from the standpoints of the basic concepts and the device architectures. The underlying mechanisms for the focusing effect and the tuning capability inherent to the lens configuration are described. Rece

In the previous paper we studied the transport coefficients of quark–gluon plasma in finite temperature and finite density in vector and tensor modes. In this paper, we extend it to the scalar modes. We work out the decoupling problem and hydrodynamic analysis for the sound mode in charged AdS black hole and calculate the sound velocity, the charge susceptibility and the electrical conductivity. We find that Einstein relation among the conductivity, the diffusion constant and the susceptibility

Gauge/Gravity duality as a theory of matter needs a systematic way to characterise a system. We suggest a `dimensional lifting' of the least irrelevant interaction to the bulk theory. As an example, we consider the spin-orbit interaction, which causes magneto-electric interaction term. We show that its lifting is an axionic coupling. We present an exact and analytic solution describing diamagnetic response. Experimental data on annealed graphite shows a remarkable similarity to our theoretical r