76,293 research outputs found
Riccati equations for holographic 2-point functions
Any second order homogeneous linear ordinary differential equation can be
transformed into a first order non-linear Riccati equation. We argue that the
Riccati form of the linearized fluctuation equations that determine the
holographic 2-point functions simplifies considerably the numerical computation
of such 2-point functions and of the corresponding transport coefficients by
computing directly the response functions, eliminating the arbitrary source
from the start. Moreover, it provides a neat criterion for the infrared
regularity of the fluctuations. In particular, it is shown that the infrared
regularity conditions for scalar and tensor fluctuations coincide, and hence
they are either both regular or both singular. We demonstrate our numerical
recipe based on the Riccati equations by computing the holographic 2-point
functions for the stress tensor and a scalar operator in a number of
asymptotically anti de Sitter backgrounds of bottom up scalar-gravity models.
Analytical results are obtained for the 2-point function of the transverse
traceless part of the stress tensor in two confining geometries, including a
geometry that belongs to the class of IHQCD. We find that in this background
the spin-2 spectrum is linear and, as expected, the position space 2-point
function decays exponentially at large distances at a rate proportional to the
confinement scale.Comment: 33 pages, 5 figures, 2 appendices. Changes with respect to V1: major
extension of the numerical and analytical analysis. Added lemma 5.1,
appendices A and B and references. Corrected typo
A study of search intermediary working notes: implications for IR system design
This paper reports findings from an exploratory study investigating working notes created during encoding and external storage (EES) processes, by human search intermediates using a Boolean information retrieval (JR) system. EES processes have been an important area of research in educational contexts where students create and use notes to facilitate learning. In the context of interactive IR, encoding can be conceptualized as the process of creating working notes to help in the understanding and translating a user's information problem into a search strategy suitable for use with an IR system. External storage is the process of using working notes to facilitate interaction with IR systems. Analysis of 221 sets of working notes created by human search intermediaries revealed extensive use of EES processes and the creation of working notes of textual, numerical and graphical entities. Nearly 70% of recorded working notes were textual/numerical entities, nearly 30% were graphical entities and 0.73% were indiscernible. Segmentation devices were also used in 48% of the working notes. The creation of working notes during EES processes was a fundamental element within the mediated, interactive IR process. Implications for the design of IR interfaces to support users' EES processes and further research is discussed
Mini-Black-Hole production at RHIC and LHC
We argue that heavy-ion collisions provide the best testing ground for
mini-black hole physics as for the gravity dual of YM and
give concrete evidence for a new extra dimension, that is visible only to the
strong interactions. We analyse the process of production evolution and decay
of the mini-black-holes by using recent results on gravity duals of YM. There
are several novelties compared with the traditional story of black hole
evaporation, including Bjorken scaling instead of sphericity, evaporation via
bubble nucleation instead of the Hawking mechanism and lepton-poor final
states. Multiplicities are estimated using shock-wave scattering techniques. It
is argued that high-multiplicity/high energy pp collisions will also show
similar characteristics of mini-black-hole production and decay.Comment: Latex, 10 pages, 2 figure
Holography and the conformal window in the Veneziano limit
We discuss holographic QCD in the Veneziano limit (the V-QCD models),
concentrating on phenomena near the "conformal" phase transition taking place
at a critical value of the ratio x = N_f/N_c. In particular, we review the
results for the S-parameter, the technidilaton, and the masses of the mesons.Comment: 15 pages, 7 figures. Contribution to Sakata Memorial KMI Workshop on
"Origin of Mass and Strong Coupling Gauge Theories (SCGT15)", 3-6 March 2015,
Nagoya Universit
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