157 research outputs found
Dangerous Angular KK/Glueball Relics in String Theory Cosmology
The presence of Kaluza-Klein particles in the universe is a potential
manifestation of string theory cosmology. In general, they can be present in
the high temperature bath of the early universe. In particular examples, string
theory inflation often ends with brane-antibrane annihilation followed by the
energy cascading through massive closed string loops to KK modes which then
decay into lighter standard model particles. However, massive KK modes in the
early universe may become dangerous cosmological relics if the inner manifold
contains warped throat(s) with approximate isometries. In the complimentary
picture, in the AdS/CFT dual gauge theory with extra symmetries, massive
glueballs of various spins become the dangerous cosmological relics. The decay
of these angular KK modes/glueballs, located around the tip of the throat, is
caused by isometry breaking which results from gluing the throat to the compact
CY manifold. We address the problem of these angular KK particles/glueballs,
studying their interactions and decay channels, from the theory side, and the
resulting cosmological constraints on the warped compactification parameters,
from the phenomenology side. The abundance and decay time of the long-lived
non-relativistic angular KK modes depend strongly on the parameters of the
warped geometry, so that observational constraints rule out a significant
fraction of the parameter space. In particular, the coupling of the angular KK
particles can be weaker than gravitational.Comment: 58 pages, 11 figures, published versio
Using Sensor Metadata Streams to Identify Topics of Local Events in the City
In this paper, we study the emerging Information Retrieval (IR) task of local event retrieval using sensor metadata streams. Sensor metadata streams include information such as the crowd density from video processing, audio classifications, and social media activity. We propose to use these metadata streams to identify the topics of local events within a city, where each event topic corresponds to a set of terms representing a type of events such as a concert or a protest. We develop a supervised approach that is capable of mapping sensor metadata observations to an event topic. In addition to using a variety of sensor metadata observations about the current status of the environment as learning features, our approach incorporates additional background features to model cyclic event patterns. Through experimentation with data collected from two locations in a major Spanish city, we show that our approach markedly outperforms an alternative baseline. We also show that modelling background information improves event topic identification
Gravitational Radiation from First-Order Phase Transitions
It is believed that first-order phase transitions at or around the GUT scale
will produce high-frequency gravitational radiation. This radiation is a
consequence of the collisions and coalescence of multiple bubbles during the
transition. We employ high-resolution lattice simulations to numerically evolve
a system of bubbles using only scalar fields, track the anisotropic stress
during the process and evolve the metric perturbations associated with
gravitational radiation. Although the radiation produced during the bubble
collisions has previously been estimated, we find that the coalescence phase
enhances this radiation even in the absence of a coupled fluid or turbulence.
We comment on how these simulations scale and propose that the same enhancement
should be found at the Electroweak scale; this modification should make direct
detection of a first-order electroweak phase transition easier.Comment: 7 pages, 7 figure
Quality of Experience in UHD-1 Phase 2 television: the contribution of UHD+ HFR technology
A key factor to determine the quality of experience (QoE) of a video is its capability to convey the large spectrum of perceptual phenomena that our eyes can sense in real life. In order to meet this demand, the recent DVB UHD-1 Phase 2 specification employs new video features, such as higher spatial resolutions (4K/8K) and High Frame Rate (HFR). The first enables larger field of view and level of details, while the second offers sharper images of moving objects going well beyond the current frame rates. While the contribution of each of these technologies to QoE has been investigated individually, in this paper we are interested to study their interaction, and in quantifying the benefits to users from their combination. To this end, we conduct a subjective test on compressed UHD+HFR content on a recent display capable of reproducing 100 pictures per second at 2160p resolution, with the goal to assess the increase in QoE of UHD and HFR with respect to conventional video, both individually and in combination. The results indicate that for content with fast motion, at higher bitrates the combination of UHD and HFR significantly improves the QoE compared to that obtained when these features are used individually
Preheating with Trilinear Interactions: Tachyonic Resonance
We investigate the effects of bosonic trilinear interactions in preheating
after chaotic inflation. A trilinear interaction term allows for the complete
decay of the massive inflaton particles, which is necessary for the transition
to radiation domination. We found that typically the trilinear term is
subdominant during early stages of preheating, but it actually amplifies
parametric resonance driven by the four-legs interaction. In cases where the
trilinear term does dominate during preheating, the process occurs through
periodic tachyonic amplifications with resonance effects, which is so effective
that preheating completes within a few inflaton oscillations. We develop an
analytic theory of this process, which we call tachyonic resonance. We also
study numerically the influence of trilinear interactions on the dynamics after
preheating. The trilinear term eventually comes to dominate after preheating,
leading to faster rescattering and thermalization than could occur without it.
Finally, we investigate the role of non-renormalizable interaction terms during
preheating. We find that if they are present they generally dominate (while
still in a controllable regime) in chaotic inflation models. Preheating due to
these terms proceeds through a modified form of tachyonic resonance.Comment: 19 pages, 10 figures, refs added, published versio
JPSEC for Secure Imaging in JPEG 2000
In this paper, we first review the on-going JPSEC standardization activity. Its goal is to extend the baseline JPEG 2000 specification to provide a standardized framework for secure imaging, in order to support tools needed to secure digital images, such as content protection, data integrity check, authentication, and conditional access control. We then present two examples of JPSEC tools. The first one is a technique for secure scalable streaming and secure transcoding. It allows the protected JPSEC codestream to be transcoded while preserving the protection, i.e. without requiring unprotecting (e.g. decrypting) the codestream. The second one is a technique for conditional access control. It can be used for access control by resolution or quality, but also by regions of interest
Study of gravitational radiation from cosmic domain walls
In this paper, following the previous study, we evaluate the spectrum of
gravitational wave background generated by domain walls which are produced if
some discrete symmetry is spontaneously broken in the early universe. We apply
two different methods to calculate the gravitational wave spectrum: One is to
calculate the gravitational wave spectrum directly from numerical simulations,
and another is to calculate it indirectly by estimating the unequal time
anisotropic stress power spectrum of the scalar field. Both analysises indicate
that the slope of the spectrum changes at two characteristic frequencies
corresponding to the Hubble radius at the decay of domain walls and the width
of domain walls, and that the spectrum between these two characteristic
frequencies becomes flat or slightly red tilted. The second method enables us
to evaluate the GW spectrum semi-analytically for the frequencies which can not
be resolved in the finite box lattice simulations, but relies on the
assumptions for the unequal time correlations of the source.Comment: 17 pages, 9 figures; revised version of the manuscript, accepted for
publication in JCA
Studying error resilience performance for a feedback channel based transform domain Wyner-Ziv video codec
Wyner-Ziv (WZ) video coding is an emerging video coding paradigm based on two major Information Theory results: the Slepian-Wolf and Wyner-Ziv theorems. One of the most interesting and used WZ video i coding architectures makes use of a feedback channel (FC) to perform c rate control at the decoder; in this context, the Slepian-Wolf coding t module is typically based on turbo coding with puncturing. Because WZ coding is not based on the prediction loop used in conventional video coding but rather on a statistical approach where a decoder estimation of the frame to be coded is 'corrected' by the encoder, it provides intrinsic error resilience capabilities. This paper intends to study the error resilience performance of a feedback channel based transform domain WZ codec using appropriate scenarios and conditions, notably in comparison with the best performing H. 264/AVC standard.info:eu-repo/semantics/acceptedVersio
Gravitational waves from brane-world inflation with induced gravity
We calculate the amplitude of gravitational waves produced by inflation on a
de Sitter brane embedded in five-dimensional anti-de Sitter bulk spacetime,
extending previous calculations in Randall-Sundrum type cosmology to include
the effect of induced gravity corrections on the brane. These corrections arise
via a term in the brane action that is proportional to the brane Ricci scalar.
We find that, as in the Randall-Sundrum case, there is a mass gap between the
discrete zero-mode and a continuum of massive bulk modes, which are too heavy
to be excited during inflation. We give the normalization of the zero-mode as a
function of the Hubble rate on the brane and are thus able to calculate the
high energy correction to the spectrum of gravitational wave (tensor) modes
excited on large scales during inflation from initial vacuum fluctuations on
small scales. We also calculate the amplitude of density (scalar) perturbations
expected due to inflaton fluctuations on the brane, and show that the usual
four-dimensional consistency relation for the tensor/scalar ratio remains valid
for brane inflation with induced gravity corrections.Comment: 8 pages, 2 figure
General Gauss-Bonnet brane cosmology
We consider 5-dimensional spacetimes of constant 3-dimensional spatial
curvature in the presence of a bulk cosmological constant. We find the general
solution of such a configuration in the presence of a Gauss-Bonnet term. Two
classes of non-trivial bulk solutions are found. The first class is valid only
under a fine tuning relation between the Gauss-Bonnet coupling constant and the
cosmological constant of the bulk spacetime. The second class of solutions are
static and are the extensions of the AdS-Schwarzchild black holes. Hence in the
absence of a cosmological constant or if the fine tuning relation is not true,
the generalised Birkhoff's staticity theorem holds even in the presence of
Gauss-Bonnet curvature terms. We examine the consequences in brane world
cosmology obtaining the generalised Friedmann equations for a perfect fluid
3-brane and discuss how this modifies the usual scenario.Comment: 20 pages, no figures, typos corrected, refs added, section IV changed
yielding novel result
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