200 research outputs found
Local quenches and quantum chaos from higher spin perturbations
We study local quenches in 1+1 dimensional conformal field theories at large-c by operators carrying higher spin charge. Viewing such states as solutions in Chern-Simons theory, representing infalling massive particles with spin-three charge in the BTZ back- ground, we use the Wilson line prescription to compute the single-interval entanglement entropy (EE) and scrambling time following the quench. We find that the change in EE is finite (and real) only if the spin-three charge q is bounded by the energy of the perturbation E, as |q|/c < E^2/c^2. We show that the Wilson line/EE correlator deep in the quenched regime and its expansion for small quench widths overlaps with the Regge limit for chaos of the out-of-time-ordered correlator. We further find that the scrambling time for the two- sided mutual information between two intervals in the thermofield double state increases with increasing spin-three charge, diverging when the bound is saturated. For larger values of the charge, the scrambling time is shorter than for pure gravity and controlled by the spin-three Lyapunov exponent 4π/β. In a CFT with higher spin chemical potential, dual to a higher spin black hole, we find that the chemical potential must be bounded to ensure that the mutual information is a concave function of time and entanglement speed is less than the speed of light. In this case, a quench with zero higher spin charge yields the same Lyapunov exponent as pure Einstein gravity
Higher dimensional generalisations of the SYK model
We discuss a 1+1 dimensional generalization of the Sachdev-Ye-Kitaev model.
The model contains Majorana fermions at each lattice site with a
nearest-neighbour hopping term. The SYK random interaction is restricted to low
momentum fermions of definite chirality within each lattice site. This gives
rise to an ordinary 1+1 field theory above some energy scale and a low energy
SYK-like behavior. We exhibit a class of low-pass filters which give rise to a
rich variety of hyperscaling behaviour in the IR. We also discuss another set
of generalizations which describes probing an SYK system with an external
fermion, together with the new scaling behavior they exhibit in the IR.Comment: 23 pages, 3 figures. Minor change
Scrambling time from local perturbations of the eternal BTZ black hole
We compute the mutual information between finite intervals in two non-compact
2d CFTs in the thermofield double formulation after one of them has been
locally perturbed by a primary operator at some time in the large
limit. We determine the time scale, called the scrambling time, at which
the mutual information vanishes and the original entanglement between the
thermofield double gets destroyed by the perturbation. We provide a holographic
description in terms of a free falling particle in the eternal BTZ black hole
that exactly matches our CFT calculations. Our results hold for any time
. In particular, when the latter is large, they reproduce the bulk
shock-wave propagation along the BTZ horizon description.Comment: 37 pages, 5 figure
Butterfly effect and holographic mutual information under external field and spatial noncommutativity
Nonperturbative aspects of ABJM theory
Using the matrix model which calculates the exact free energy of ABJM theory
on S^3 we study non-perturbative effects in the large N expansion of this
model, i.e., in the genus expansion of type IIA string theory on AdS4xCP^3. We
propose a general prescription to extract spacetime instanton actions from
general matrix models, in terms of period integrals of the spectral curve, and
we use it to determine them explicitly in the ABJM matrix model, as exact
functions of the 't Hooft coupling. We confirm numerically that these
instantons control the asymptotic growth of the genus expansion. Furthermore,
we find that the dominant instanton action at strong coupling determined in
this way exactly matches the action of an Euclidean D2-brane instanton wrapping
RP^3.Comment: 26 pages, 14 figures. v2: small corrections, final version published
in JHE
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