60,252 research outputs found
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
-wave heavy meson are presented in both general and heavy quark frameworks.
Within the light-front approach, the leading twist light-cone distribution
amplitudes, , and their relevant decay constants of heavy
pseudoscalar and vector mesons, , 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 -moments of 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, and , are compared
with the -meson LCDAs, , suggested by the other theoretical
groups.Comment: 25 pages, 3 figures, 4 tables, some typos are corrected, version to
be published in Phys. Rev.
Quantum correlations in topological quantum phase transitions
We study the quantum correlations in a 2D system that possesses a topological
quantum phase transition. The quantumness of two-body correlations is measured
by quantum discord. We calculate both the correlation of two local spins and
that of an arbitrary spin with the rest of the lattice. It is notable that
local spins are classically correlated, while the quantum correlation is hidden
in the global lattice. This is different from other systems which are not
topologically orderd. Moreover, the mutual information and global quantum
discord show critical behavior in the topological quantum phase transition.Comment: 6 pages, 3 figure
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