576 research outputs found
Measuring Black Hole Formations by Entanglement Entropy via Coarse-Graining
We argue that the entanglement entropy offers us a useful coarse-grained
entropy in time-dependent AdS/CFT. We show that the total von-Neumann entropy
remains vanishing even when a black hole is created in a gravity dual, being
consistent with the fact that its corresponding CFT is described by a
time-dependent pure state. We analytically calculate the time evolution of
entanglement entropy for a free Dirac fermion on a circle following a quantum
quench. This is interpreted as a toy holographic dual of black hole creations
and annihilations. It is manifestly free from the black hole information
problem.Comment: 25 pages, Latex, 8 figure
Non-equilibrium Dynamics of O(N) Nonlinear Sigma models: a Large-N approach
We study the time evolution of the mass gap of the O(N) non-linear sigma
model in 2+1 dimensions due to a time-dependent coupling in the large-
limit. Using the Schwinger-Keldysh approach, we derive a set of equations at
large which determine the time dependent gap in terms of the coupling.
These equations lead to a criterion for the breakdown of adiabaticity for slow
variation of the coupling leading to a Kibble-Zurek scaling law. We describe a
self-consistent numerical procedure to solve these large- equations and
provide explicit numerical solutions for a coupling which starts deep in the
gapped phase at early times and approaches the zero temperature equilibrium
critical point in a linear fashion. We demonstrate that for such a
protocol there is a value of the coupling where the gap
function vanishes, possibly indicating a dynamical instability. We study the
dependence of on both the rate of change of the coupling and
the initial temperature. We also verify, by studying the evolution of the mass
gap subsequent to a sudden change in , that the model does not display
thermalization within a finite time interval and discuss the implications
of this observation for its conjectured gravitational dual as a higher spin
theory in .Comment: 22 pages, 9 figures. Typos corrected, references rearranged and
added.v3 : sections rearranged, abstract modified, comment about Kibble-Zurek
scaling correcte
Energy loss in a strongly coupled anisotropic plasma
We study the energy loss of a rotating infinitely massive quark moving, at
constant velocity, through an anisotropic strongly-coupled N=4 plasma from
holography. It is shown that, similar to the isotropic plasma, the energy loss
of the rotating quark is due to either the drag force or radiation with a
continuous crossover from drag-dominated regime to the radiation dominated
regime. We find that the anisotropy has a significant effect on the energy loss
of the heavy quark, specially in the crossover regime. We argue that the energy
loss due to radiation in anisotropic media is less than the isotropic case.
Interestingly this is similar to analogous calculations for the energy loss in
weakly coupled anisotropic plasma.Comment: 26+1 pages, 10 figures, typos fixe
Expression quantitative trait loci are highly sensitive to cellular differentiation state
Blood cell development from multipotent hematopoietic stem cells to specialized blood cells is accompanied by drastic changes in gene expression for which the triggers remain mostly unknown. Genetical genomics is an approach linking natural genetic variation to gene expression variation, thereby allowing the identification of genomic loci containing gene expression modulators (eQTLs). In this paper, we used a genetical genomics approach to analyze gene expression across four developmentally close blood cell types collected from a large number of genetically different but related mouse strains. We found that, while a significant number of eQTLs (365) had a consistent âstaticâ regulatory effect on gene expression, an even larger number were found to be very sensitive to cell stage. As many as 1,283 eQTLs exhibited a âdynamicâ behavior across cell types. By looking more closely at these dynamic eQTLs, we show that the sensitivity of eQTLs to cell stage is largely associated with gene expression changes in target genes. These results stress the importance of studying gene expression variation in well-defined cell populations. Only such studies will be able to reveal the important differences in gene regulation between different ce
Holographic Evolution of Entanglement Entropy
We study the evolution of entanglement entropy in a 2-dimensional
equilibration process that has a holographic description in terms of a Vaidya
geometry. It models a unitary evolution in which the field theory starts in a
pure state, its vacuum, and undergoes a perturbation that brings it far from
equilibrium. The entanglement entropy in this set up provides a measurement of
the quantum entanglement in the system. Using holographic techniques we recover
the same result obtained before from the study of processes triggered by a
sudden change in a parameter of the hamiltonian, known as quantum quenches.
Namely, entanglement in 2-dimensional conformal field theories propagates with
velocity v^2=1. Both in quantum quenches and in the Vaidya model equilibration
is only achieved at the local level. Remarkably, the holographic derivation of
this last fact requires information from behind the apparent horizon generated
in the process of gravitational collapse described by the Vaidya geometry. In
the early stages of the evolution the apparent horizon seems however to play no
relevant role with regard to the entanglement entropy. We speculate on the
possibility of deriving a thermalization time for occupation numbers from our
analysis.Comment: 26 pages, 10 figure
Probing strongly coupled anisotropic plasma
We calculate the static potential, the drag force and the jet quenching
parameter in strongly coupled anisotropic N=4 super Yang-Mills plasma. We find
that the jet quenching is in general enhanced in presence of anisotropy
compared to the isotropic case and that its value depends strongly on the
direction of the moving quark and the direction along which the momentum
broadening occurs. The jet quenching is strongly enhanced for a quark moving
along the anisotropic direction and momentum broadening happens along the
transverse one. The parameter gets lower for a quark moving along the
transverse direction and the momentum broadening considered along the
anisotropic one. Finally, a weaker enhancement is observed when the quark moves
in the transverse plane and the broadening occurs on the same plane. The drag
force for quark motion parallel to the anisotropy is always enhanced. For
motion in the transverse space the drag force is enhanced compared to the
isotropic case only for quarks having velocity above a critical value. Below
this critical value the force is decreased. Moreover, the drag force along the
anisotropic direction is always stronger than the force in the transverse
space. The diffusion time follows exactly the inverse relations of the drag
forces. The static potential is decreased and stronger decrease observed for
quark-antiquark pair aligned along the anisotropic direction than the
transverse one. We finally comment on our results and elaborate on their
similarities and differences with the weakly coupled plasmas.Comment: 1+44 pages, 18 Figures; Added results on static force; Added
references; version published in JHE
Early-Time Energy Loss in a Strongly-Coupled SYM Plasma
We carry out an analytic study of the early-time motion of a quark in a
strongly-coupled maximally-supersymmetric Yang-Mills plasma, using the AdS/CFT
correspondence. Our approach extracts the first thermal effects as a small
perturbation of the known quark dynamics in vacuum, using a double expansion
that is valid for early times and for (moderately) ultrarelativistic quark
velocities. The quark is found to lose energy at a rate that differs
significantly from the previously derived stationary/late-time result: it
scales like T^4 instead of T^2, and is associated with a friction coefficient
that is not independent of the quark momentum. Under conditions representative
of the quark-gluon plasma as obtained at RHIC, the early energy loss rate is a
few times smaller than its late-time counterpart. Our analysis additionally
leads to thermally-corrected expressions for the intrinsic energy and momentum
of the quark, in which the previously discovered limiting velocity of the quark
is found to appear naturally.Comment: 39 pages, no figures. v2: Minor corrections and clarifications.
References added. Version to be published in JHE
Chiral drag force
We provide a holographic evaluation of novel contributions to the drag force
acting on a heavy quark moving through strongly interacting plasma. The new
contributions are chiral in that they act in opposite directions in plasmas
containing an excess of left- or right-handed quarks and in that they are
proportional to the coefficient of the axial anomaly. These new contributions
to the drag force act either parallel to or antiparallel to an external
magnetic field or to the vorticity of the fluid plasma. In all these respects,
these contributions to the drag force felt by a heavy quark are analogous to
the chiral magnetic effect on light quarks. However, the new contribution to
the drag force is independent of the electric charge of the heavy quark and is
the same for heavy quarks and antiquarks. We show that although the chiral drag
force can be non-vanishing for heavy quarks that are at rest in the local fluid
rest frame, it does vanish for heavy quarks that are at rest in a suitably
chosen frame. In this frame, the heavy quark at rest sees counterpropagating
momentum and charge currents, both proportional to the axial anomaly
coefficient, but feels no drag force. This provides strong concrete evidence
for the absence of dissipation in chiral transport, something that has been
predicted previously via consideration of symmetries. Along the way to our
principal results, we provide a general calculation of the corrections to the
drag force due to the presence of gradients in the flowing fluid in the
presence of a nonzero chemical potential. We close with a consequence of our
result that is at least in principle observable in heavy ion collisions, namely
an anticorrelation between the direction of the CME current for light quarks in
a given event and the direction of the kick given to the momentum of all the
heavy quarks and antiquarks in that event.Comment: 28 pages, small improvement to the discussion of gravitational
anomaly, references adde
- âŠ