3,437 research outputs found
The dS/dS Correspondence
We present a holographic duality for the de Sitter static patch which
consolidates basic features of its geometry and the behavior of gravity and
brane probes, valid on timescales short compared to the decay or Poincare
recurrence times. Namely de Sitter spacetime in dimensions with
curvature radius is holographically dual to two conformal field theories on
, cut off at an energy scale 1/R where they couple to each other
and to dimensional gravity. As part of our analysis, we study brane
probes in de Sitter and thermal Anti de Sitter spaces, and interpret the terms
in the corresponding DBI action via strongly coupled thermal field theory. This
provides a dual field theoretic interpretation of the fact that probes take
forever to reach a horizon in general relativity.Comment: 29 pages, harvmac big; 3 figures; v2: references added, minor typo
fixe
The Value of Patents in the United States and Abroad: Guidelines for the General Practitioner
The Value of Patents in the United States and Abroad: Guidelines for the General Practitioner
Attractor Explosions and Catalyzed Vacuum Decay
We present a mechanism for catalyzed vacuum bubble production obtained by
combining moduli stabilization with a generalized attractor phenomenon in which
moduli are sourced by compact objects. This leads straightforwardly to a class
of examples in which the Hawking decay process for black holes unveils a bubble
of a different vacuum from the ambient one, generalizing the new endpoint for
Hawking evaporation discovered recently by Horowitz. Catalyzed vacuum bubble
production can occur for both charged and uncharged bodies, including
Schwarzschild black holes for which massive particles produced in the Hawking
process can trigger vacuum decay. We briefly discuss applications of this
process to the population and stability of metastable vacua.Comment: 26 pages harvmac big; 2 figure
Dimensional Duality
We show that string theory on a compact negatively curved manifold,
preserving a U(1)^{b_1} winding symmetry, grows at least b_1 new effective
dimensions as the space shrinks. The winding currents yield a "D-dual"
description of a Riemann surface of genus h in terms of its 2h dimensional
Jacobian torus, perturbed by a closed string tachyon arising as a potential
energy term in the worldsheet sigma model. D-branes on such negatively curved
manifolds also reveal this structure, with a classical moduli space consisting
of a b_1-torus. In particular, we present an AdS/CFT system which offers a
non-perturbative formulation of such supercritical backgrounds. Finally, we
discuss generalizations of this new string duality.Comment: 25 pages, harvmac. v2: fixed typo. v3: fixed typos and added ref
Is Attentional Blink a Byproduct of Neocortical Attractors?
This study proposes a computational model for attentional blink or âblink of the mind,â a phenomenon where a human subject misses perception of a later expected visual pattern as two expected visual patterns are presented less than 500âms apart. A neocortical patch modeled as an attractor network is stimulated with a sequence of 14 patterns 100âms apart, two of which are expected targets. Patterns that become active attractors are considered recognized. A neocortical patch is represented as a square matrix of hypercolumns, each containing a set of minicolumns with synaptic connections within and across both minicolumns and hypercolumns. Each minicolumn consists of locally connected layer 2/3 pyramidal cells with interacting basket cells and layer 4 pyramidal cells for input stimulation. All neurons are implemented using the HodgkinâHuxley multi-compartmental cell formalism and include calcium dynamics, and they interact via saturating and depressing AMPA/NMDA and GABAA synapses. Stored patterns are encoded with global connectivity of minicolumns across hypercolumns and active patterns compete as the result of lateral inhibition in the network. Stored patterns were stimulated over time intervals to create attractor interference measurable with synthetic spike traces. This setup corresponds with item presentations in human visual attentional blink studies. Stored target patterns were depolarized while distractor patterns where hyperpolarized to represent expectation of items in working memory. Simulations replicated the basic attentional blink phenomena and showed a reduced blink when targets were more salient. Studies on the inhibitory effect of benzodiazepines on attentional blink in human subjects were compared with neocortical simulations where the GABAA receptor conductance and decay time were increased. Simulations showed increases in the attentional blink duration, agreeing with observations in human studies. In addition, sensitivity analysis was performed on key parameters of the model, including Ca2+-gated K+ channel conductance, synaptic depression, GABAA channel conductance and the NMDA/AMPA ratio of charge entry
The GHOSTS survey. II. The diversity of Halo Color and Metallicity Profiles of Massive Disk Galaxies
We study the stellar halo color properties of six nearby massive highly
inclined disk galaxies using Hubble Space Telescope Advanced Camera for Surveys
and Wide Field Camera 3 observations in both F606W and F814W filters from the
GHOSTS survey. The observed fields, placed both along the minor and major axis
of each galaxy, probe the stellar outskirts out to projected distances of ~
50-70 kpc from their galactic centre along the minor axis. The 50% completeness
levels of the color magnitude diagrams are typically at two mag below the tip
of the red giant branch. We find that all galaxies have extended stellar halos
out to ~ 50 kpc and two out to ~ 70 kpc. We determined the halo color
distribution and color profile for each galaxy using the median colors of stars
in the RGB. Within each galaxy we find variations in the median colors as a
function of radius which likely indicates population variations, reflecting
that their outskirts were built from several small accreted objects. We find
that half of the galaxies (NGC 0891, NGC 4565, and NGC 7814) present a clear
negative color gradient, reflecting a declining metallicity in their halos; the
other have no significant color or population gradient. In addition,
notwithstanding the modest sample size of galaxies, there is no strong
correlation between their halo color/metallicity or gradient with galaxy's
properties such as rotational velocity or stellar mass. The diversity in halo
color profiles observed in the GHOSTS galaxies qualitatively supports the
predicted galaxy-to-galaxy scatter in halo stellar properties; a consequence of
the stochasticity inherent in the assembling history of galaxies.Comment: Accepted by MNRAS, 31 pages, 18 figures. Appendix added and some
editions to match accepted version. Conclusions unchange
- âŠ