1,789 research outputs found
An Uneventful Horizon in Two Dimensions
We investigate the possibility of firewalls in the Einstein-dilaton gravity
model of CGHS. We use the results of the numerical simulation carried out by
Ashtekar et al. to demonstrate that firewalls are absent and the horizon is
drama free. We show that the lack of a firewall is consistent because the model
does not satisfy one of the postulates of black hole complementarity. In
particular, we show that the Hawking radiation is not pure, and is completely
entangled with a long-lived remnant beyond the last ray.Comment: 28 pages, 4 figure
Holographic Reconstruction of General Bulk Surfaces
We propose a reconstruction of general bulk surfaces in any dimension in
terms of the differential entropy in the boundary field theory. In particular,
we extend the proof of Headrick et al. to calculate the area of a general class
of surfaces, which have a 1-parameter foliation over a closed manifold. The
area can be written in terms of extremal surfaces whose boundaries lie on
ring-like regions in the field theory. We discuss when this construction has a
description in terms of spatial entanglement entropy and suggest lessons for a
more complete and covariant approach.Comment: 21 pages, 10 figures; v2: minor clarifications, references added,
published versio
Spinning Geodesic Witten Diagrams
We present an expression for the four-point conformal blocks of symmetric
traceless operators of arbitrary spin as an integral over a pair of geodesics
in Anti-de Sitter space, generalizing the geodesic Witten diagram formalism of
Hijano et al [arXiv:1508.00501] to arbitrary spin. As an intermediate step in
the derivation, we identify a convenient basis of bulk three-point interaction
vertices which give rise to all possible boundary three point structures. We
highlight a direct connection between the representation of the conformal block
as a geodesic Witten diagram and the shadow operator formalism.Comment: 28+6 pages, 8 figure
Akt-dependent Pp2a activity is required for epidermal barrier formation during late embryonic development
Acquisition of epidermal barrier function occurs late in mouse gestation. Several days before birth a wave of barrier acquisition sweeps across murine fetal skin, converging on dorsal and ventral midlines. We investigated the molecular pathways active during epidermal barrier formation. Akt signaling increased as the barrier wave crossed epidermis and Jun was transiently dephosphorylated. Inhibitor experiments on embryonic explants showed that the dephosphorylation of Jun was dependent on both Akt and protein phosphatase 2A (Pp2a). Inhibition of Pp2a and Akt signaling also caused defects in epidermal barrier formation. These data are compatible with a model for developmental barrier acquisition mediated by Pp2a regulation of Jun dephosphorylation, downstream of Akt signaling. Support for this model was provided by siRNA-mediated knockdown of Ppp2r2a (Pr55α or B55α), a regulatory subunit of Pp2a expressed in an Akt-dependent manner in epidermis during barrier formation. Ppp2r2a reduction caused significant increase in Jun phosphorylation and interfered with the acquisition of barrier function, with barrier acquisition being restored by inhibition of Jun phosphorylation. Our data provide strong evidence that Ppp2r2a is a regulatory subunit of Pp2a that targets this phosphatase to Jun, and that Pp2a action is necessary for barrier formation. We therefore describe a novel Akt-dependent Pp2a activity that acts at least partly through Jun to affect initial barrier formation during late embryonic epidermal development
Integral Geometry and Holography
We present a mathematical framework which underlies the connection between
information theory and the bulk spacetime in the AdS/CFT
correspondence. A key concept is kinematic space: an auxiliary Lorentzian
geometry whose metric is defined in terms of conditional mutual informations
and which organizes the entanglement pattern of a CFT state. When the field
theory has a holographic dual obeying the Ryu-Takayanagi proposal, kinematic
space has a direct geometric meaning: it is the space of bulk geodesics studied
in integral geometry. Lengths of bulk curves are computed by kinematic volumes,
giving a precise entropic interpretation of the length of any bulk curve. We
explain how basic geometric concepts -- points, distances and angles -- are
reflected in kinematic space, allowing one to reconstruct a large class of
spatial bulk geometries from boundary entanglement entropies. In this way,
kinematic space translates between information theoretic and geometric
descriptions of a CFT state. As an example, we discuss in detail the static
slice of AdS whose kinematic space is two-dimensional de Sitter space.Comment: 23 pages + appendices, including 23 figures and an exercise sheet
with solutions; a Mathematica visualization too
Bulk and Transhorizon Measurements in AdS/CFT
We discuss the construction of bulk operators in asymptotically AdS
spacetimes, including the interiors of AdS black holes. We use this to address
the question "If Schrodinger's cat were behind the horizon of an AdS black
hole, could we determine its state by a measurement in the dual CFT?"Comment: 32 pages, 5 figures. v2: Author added, appendix on spacelike Green's
function added, discussion of non-dependence on boundary Hamiltonian expande
Modular Berry Connection
The Berry connection describes transformations induced by adiabatically
varying Hamiltonians. We study how zero modes of the modular Hamiltonian are
affected by varying the region that supplies the modular Hamiltonian. In the
vacuum of a 2d CFT, global conformal symmetry singles out a unique modular
Berry connection, which we compute directly and in the dual AdS picture. In
certain cases, Wilson loops of the modular Berry connection compute lengths of
curves in AdS, reproducing the differential entropy formula. Modular Berry
transformations can be measured by bulk observers moving with varying
accelerations.Comment: 5 pages, 2 figures. Some clarifications adde
The privileged place of home: Place, memory and the disease of nostalgia
In the centuries prior to the advent of printing, scholars who practised the ars memorativa, often undertook travel specifically in order to expand their repertoires of backgrounds for their memory palaces. Thus the act of travelling became associated with not just the pursuit of knowledge and experience, but also with memory. However, in the eighteenth and nineteenth centuries this association with memory and travel was tragically inverted with the rising incidence of a much feared disease, known as Nostalgia. Nostalgia was a sometimes fatal bout of homesickness, a form of melancholia, which was essentially a disease of both memory and place, which while now dismissed as psychosomatic, or merely ‘nervous humours’, was surrounded with such trepidation that impending travellers went so far as to avoid prolonged absences from home in fear of contracting the disease. This paper will investigate the relationship between travel and memory as expressed through the disease of nostalgia. Tracing the disease from its seventeenth century origins through to its twentieth century transformation from ‘disease’ to ‘sentiment’, this paper will draw from the thought of Gaston Bachelard and the films of Andrey Tarkovsky to argue that the disease of nostalgia was a pathological connection to place, which, through memory, idealised and problematised one’s connection to home
- …