4,175 research outputs found
On Universality of Holographic Results for (2+1)-Dimensional CFTs on Curved Spacetimes
The behavior of holographic CFTs is constrained by the existence of a bulk
dual geometry. For example, in (2+1)-dimensional holographic CFTs living on a
static spacetime with compact spatial slices, the vacuum energy must be
nonpositive, certain averaged energy densities must be nonpositive, and the
spectrum of scalar operators is bounded from below by the Ricci scalar of the
CFT geometry. Are these results special to holographic CFTs? Here we show that
for perturbations about appropriate backgrounds, they are in fact universal to
all CFTs, as they follow from the universal behavior of two- and three-point
correlators of known operators. In the case of vacuum energy, we extend away
from the perturbative regime and make global statements about its negativity
properties on the space of spatial geometries. Finally, we comment on the
implications for dynamics which are dissipative and driven by such a vacuum
energy and we remark on similar results for the behavior of the Euclidean
partition function on deformations of flat space or the round sphere.Comment: 35+4 pages, 1 figure. v2: corrected discussion of torus to deformed
flat space; additional comments adde
Natural‐language processing applied to an ITS interface
The aim of this paper is to show that with a subset of a natural language, simple systems running on PCs can be developed that can nevertheless be an effective tool for interfacing purposes in the building of an Intelligent Tutoring System (ITS). After presenting the special characteristics of the Smalltalk/V language, which provides an appropriate environment for the development of an interface, the overall architecture of the interface module is discussed. We then show how sentences are parsed by the interface, and how interaction takes place with the user. The knowledge‐acquisition phase is subsequently described. Finally, some excerpts from a tutoring session concerned with elementary geometry are discussed, and some of the problems and limitations of the approach are illustrated
A Bound on Holographic Entanglement Entropy from Inverse Mean Curvature Flow
Entanglement entropies are notoriously difficult to compute. Large-N
strongly-coupled holographic CFTs are an important exception, where the AdS/CFT
dictionary gives the entanglement entropy of a CFT region in terms of the area
of an extremal bulk surface anchored to the AdS boundary. Using this
prescription, we show -- for quite general states of (2+1)-dimensional such
CFTs -- that the renormalized entanglement entropy of any region of the CFT is
bounded from above by a weighted local energy density. The key ingredient in
this construction is the inverse mean curvature (IMC) flow, which we suitably
generalize to flows of surfaces anchored to the AdS boundary. Our bound can
then be thought of as a "subregion" Penrose inequality in asymptotically
locally AdS spacetimes, similar to the Penrose inequalities obtained from IMC
flows in asymptotically flat spacetimes. Combining the result with positivity
of relative entropy, we argue that our bound is valid perturbatively in 1/N,
and conjecture that a restricted version of it holds in any CFT.Comment: 33+7 pages, 7 figures. v2: addressed referee comment
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