Critical magnetic field in AdS/CFT superconductor

We have studied a holographically dual description of superconductor in (2+1)-dimensions in the presence of applied magnetic field, and observed that there exists a critical value of magnetic field, below which a charged condensate can form via a second order phase transition.Comment: 8 pages, 3 figures, REVTeX v4. Typos corrected and Fig.3 replace

Spin chain from marginally deformed AdS_3 x S^3

We derive a spin chain Hamiltonian from a fast spinning string in the marginally deformed AdS(3)X S(3). This corresponds to a closed trajectory swept out by the SU(2) or SL(2) spin vector on the surface of one-parameter deformed two-sphere or hyperboloid in the background of anisotropic magnetic field interaction. In the limit of small deformation, a class of general Landau-Lifshitz equation with a nontrivial anisotropic matrix can be derived.Comment: 4 pages, 2 figures, revised for PR

A mean field approach for string condensed states

We describe a mean field technique for quantum string (or dimer) models. Unlike traditional mean field approaches, the method is general enough to include string condensed phases in addition to the usual symmetry breaking phases. Thus, it can be used to study phases and phases transitions beyond Landau's symmetry breaking paradigm. We demonstrate the technique with a simple example: the spin-1 XXZ model on the Kagome lattice. The mean field calculation predicts a number of phases and phase transitions, including a z=2 deconfined quantum critical point.Comment: 10 pages + appendix, 15 figure

Quasi-adiabatic Continuation of Quantum States: The Stability of Topological Ground State Degeneracy and Emergent Gauge Invariance

We define for quantum many-body systems a quasi-adiabatic continuation of quantum states. The continuation is valid when the Hamiltonian has a gap, or else has a sufficiently small low-energy density of states, and thus is away from a quantum phase transition. This continuation takes local operators into local operators, while approximately preserving the ground state expectation values. We apply this continuation to the problem of gauge theories coupled to matter, and propose a new distinction, perimeter law versus "zero law" to identify confinement. We also apply the continuation to local bosonic models with emergent gauge theories. We show that local gauge invariance is topological and cannot be broken by any local perturbations in the bosonic models in either continuous or discrete gauge groups. We show that the ground state degeneracy in emergent discrete gauge theories is a robust property of the bosonic model, and we argue that the robustness of local gauge invariance in the continuous case protects the gapless gauge boson.Comment: 15 pages, 6 figure

Continuous topological phase transitions between clean quantum Hall states

Continuous transitions between states with the {\em same} symmetry but different topological orders are studied. Clean quantum Hall (QH) liquids with neutral quasiparticles are shown to have such transitions. For clean bilayer (nnm) states, a continous transition to other QH states (including non-Abelian states) can be driven by increasing interlayer repulsion/tunneling. The effective theories describing the critical points at some transitions are derived.Comment: 4 pages, RevTeX, 2 eps figure

Drag Force, Jet Quenching, and AdS/QCD

In this note, two important transport observables in the RHIC experiment, relaxation time constant and jet quenching parameter, are calculated from an AdS/QCD model. A quark moving in the viscous medium such as the Quark-Gluon-Plasma is modelled by an open string whose end point travels on the boundary of a deformed AdS_5 black hole. The correction introduced via the deformed AdS_5 is believed to help us better understand the data which is expected to be measured in the RHIC.Comment: 13 pages, 4 figures, revised for PRD. Some comments have been added below Eq.(34) to avoid a misreading in comparison between our result and CFT'

Analyses of decay constants and light-cone distribution amplitudes for s-wave heavy meson

In this paper, a study of light-cone distribution amplitudes (LCDAs) for $s$-wave heavy meson are presented in both general and heavy quark frameworks. Within the light-front approach, the leading twist light-cone distribution amplitudes, $\phi_M(u)$, and their relevant decay constants of heavy pseudoscalar and vector mesons, $f_M$, have simple relations. These relations can be further simplified when the heavy quark limit is taken into consideration. After fixing the parameters that appear in both Gaussian and power-law wave functions, the corresponding decay constants are calculated and compared with those of other theoretical approaches. The curves and the first six $\xi$-moments of $\phi_M(u)$ are plotted and estimated. A conclusion is drawn from these results: Even though the values of the decay constants of the distinct mesons are almost equal, the curves of their LCDAs may have quite large differences, and vice versa. Additionally, in the heavy quark limit, the leading twist LCDAs, $\Phi_{Qq}(\omega)$ and $\Phi_{Qq}(\omega)$, are compared with the $B$-meson LCDAs, $\psi_+(\omega)$, suggested by the other theoretical groups.Comment: 25 pages, 3 figures, 4 tables, some typos are corrected, version to be published in Phys. Rev.

The superorbital variability and triple nature of the X-ray source 4U 1820-303

We perform a comprehensive analysis of the superorbital modulation in the ultracompact X-ray source 4U 1820-303, consisting of a white dwarf accreting onto a neutron star. Based on RXTE data, we measure the fractional amplitude of the source superorbital variability (with a 170-d quasi-period) in the folded and averaged light curves, and find it to be by a factor of about 2. As proposed before, the superorbital variability can be explained by oscillations of the binary eccentricity. We now present detailed calculations of the eccentricity-dependent flow through the inner Lagrangian point, and find a maximum of the eccentricity of about 0.004 is sufficient to explain the observed fractional amplitude. We then study hierarchical triple models yielding the required quasi-periodic eccentricity oscillations through the Kozai process. We find the resulting theoretical light curves to match well the observed ones. We constrain the ratio of the semimajor axes of the outer and inner systems, the component masses, and the inclination angle between the inner and outer orbits. Last but not least, we discover a remarkable and puzzling synchronization between the observed period of the superorbital variability (equal to the period of the eccentricity oscillations in our model) and the period of the general-relativistic periastron precession of the binary