257 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
Gauss-Bonnet gravity renders negative tension braneworlds unstable
We show that the Gauss-Bonnet correction to Einstein gravity induces a
gravitational tachyon mode, namely an unstable spin 2 fluctuation, in the
Randall-Sundrum I model. We demonstrate that this instability is generically
related to the presence of a negative tension brane in the set-up, with or
without -symmetry across it. Indeed it is shown that the tachyon mode is a
bound state localised on any negative tension brane of co-dimension one,
embedded in anti-de Sitter background. We discuss the possible resolution of
this instability by the inclusion of induced gravity terms on the branes or by
an effective four-dimensional cosmological constant.Comment: published versio
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
Gravitational Radiation from Preheating with Many Fields
Parametric resonances provide a mechanism by which particles can be created
just after inflation. Thus far, attention has focused on a single or many
inflaton fields coupled to a single scalar field. However, generically we
expect the inflaton to couple to many other relativistic degrees of freedom
present in the early universe. Using simulations in an expanding
Friedmann-Lema\^itre-Robertson-Walker spacetime, in this paper we show how
preheating is affected by the addition of multiple fields coupled to the
inflaton. We focus our attention on gravitational wave production--an important
potential observational signature of the preheating stage. We find that
preheating and its gravitational wave signature is robust to the coupling of
the inflaton to more matter fields.Comment: 7 pages, 8 figures, v2 submission version, thank you for comments
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
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
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
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