16,851 research outputs found
Thermodynamics of AdS/QCD
We study finite temperature properties of four dimensional QCD-like gauge
theories in the gauge theory/gravity duality picture. The gravity dual contains
two deformed 5d AdS metrics, with and without a black hole, and a dilaton. We
study the thermodynamics of the 4d boundary theory and constrain the two
metrics so that they correspond to a high and a low temperature phase separated
by a first order phase transition. The equation of state has the standard form
for the pressure of a strongly coupled fluid modified by a vacuum energy, a bag
constant. We determine the parameters of the deformation by using QCD results
for and the hadron spectrum. With these parameters, we show that the
phase transition in the 4d boundary theory and the 5d bulk Hawking-Page
transition agree. We probe the dynamics of the two phases by computing the
quark-antiquark free energy in them and confirm that the transition corresponds
to confinement-deconfinement transition.Comment: 1+19 pages, 6 figures, references added, section 3 improve
Minimal surfaces and Reggeization in the AdS/CFT correspondence
We address the problem of computing scattering amplitudes related to the
correlation function of two Wilson lines and/or loops elongated along
light-cone directions in strongly coupled gauge theories. Using the AdS/CFT
correspondence in the classical approximation, the amplitudes are shown to be
related to minimal surfaces generalizing the {\em helicoid} in various
backgrounds. Infra-red divergences appearing for Wilson lines can be factorized
out or can be cured by considering the IR finite case of correlation functions
of two Wilson loops. In non-conformal cases related to confining theories,
reggeized amplitudes with linear trajectories and unit intercept are obtained
and shown to come from the approximately flat metrics near the horizon, which
sets the scale for the Regge slope. In the conformal case the absence of
confinement leads to a different solution. A transition between both regimes
appears, in a confining theory, when varying impact parameter.Comment: 22 pages, 2 eps figures, expanded discussion, conclusions unchanged,
version to be published in Nuclear Physics
Predicting Audio Advertisement Quality
Online audio advertising is a particular form of advertising used abundantly
in online music streaming services. In these platforms, which tend to host tens
of thousands of unique audio advertisements (ads), providing high quality ads
ensures a better user experience and results in longer user engagement.
Therefore, the automatic assessment of these ads is an important step toward
audio ads ranking and better audio ads creation. In this paper we propose one
way to measure the quality of the audio ads using a proxy metric called Long
Click Rate (LCR), which is defined by the amount of time a user engages with
the follow-up display ad (that is shown while the audio ad is playing) divided
by the impressions. We later focus on predicting the audio ad quality using
only acoustic features such as harmony, rhythm, and timbre of the audio,
extracted from the raw waveform. We discuss how the characteristics of the
sound can be connected to concepts such as the clarity of the audio ad message,
its trustworthiness, etc. Finally, we propose a new deep learning model for
audio ad quality prediction, which outperforms the other discussed models
trained on hand-crafted features. To the best of our knowledge, this is the
first large-scale audio ad quality prediction study.Comment: WSDM '18 Proceedings of the Eleventh ACM International Conference on
Web Search and Data Mining, 9 page
Topologically Massive Gravity and Ricci-Cotton Flow
We consider Topologically Massive Gravity (TMG), which is three dimensional
general relativity with a cosmological constant and a gravitational
Chern-Simons term. When the cosmological constant is negative the theory has
two potential vacuum solutions: Anti-de Sitter space and Warped Anti-de Sitter
space. The theory also contains a massive graviton state which renders these
solutions unstable for certain values of the parameters and boundary
conditions. We study the decay of these solutions due to the condensation of
the massive graviton mode using Ricci-Cotton flow, which is the appropriate
generalization of Ricci flow to TMG. When the Chern-Simons coupling is small
the AdS solution flows to warped AdS by the condensation of the massive
graviton mode. When the coupling is large the situation is reversed, and warped
AdS flows to AdS. Minisuperspace models are constructed where these flows are
studied explicitly
Graph Annotations in Modeling Complex Network Topologies
The coarsest approximation of the structure of a complex network, such as the
Internet, is a simple undirected unweighted graph. This approximation, however,
loses too much detail. In reality, objects represented by vertices and edges in
such a graph possess some non-trivial internal structure that varies across and
differentiates among distinct types of links or nodes. In this work, we
abstract such additional information as network annotations. We introduce a
network topology modeling framework that treats annotations as an extended
correlation profile of a network. Assuming we have this profile measured for a
given network, we present an algorithm to rescale it in order to construct
networks of varying size that still reproduce the original measured annotation
profile.
Using this methodology, we accurately capture the network properties
essential for realistic simulations of network applications and protocols, or
any other simulations involving complex network topologies, including modeling
and simulation of network evolution. We apply our approach to the Autonomous
System (AS) topology of the Internet annotated with business relationships
between ASs. This topology captures the large-scale structure of the Internet.
In depth understanding of this structure and tools to model it are cornerstones
of research on future Internet architectures and designs. We find that our
techniques are able to accurately capture the structure of annotation
correlations within this topology, thus reproducing a number of its important
properties in synthetically-generated random graphs
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