2,288 research outputs found
Improving Third-Party Relaying for LTE-A: A Realistic Simulation Approach
In this article we propose solutions to diverse conflicts that result from
the deployment of the (still immature) relay node (RN) technology in LTE-A
networks. These conflicts and their possible solutions have been observed by
implementing standard-compliant relay functionalities on the Vienna simulator.
As an original experimental approach, we model realistic RN operation, taking
into account that transmitters are not active all the time due to half-duplex
RN operation. We have rearranged existing elements in the simulator in a manner
that emulates RN behavior, rather than implementing a standalone brand-new
component for the simulator. We also study analytically some of the issues
observed in the interaction between the network and the RNs, to draw
conclusions beyond simulation observation.
The main observations of this paper are that: ) Additional time-varying
interference management steps are needed, because the LTE-A standard employs a
fixed time division between eNB-RN and RN-UE transmissions (typical relay
capacity or throughput research models balance them optimally, which is
unrealistic nowadays); ) There is a trade-off between the time-division
constraints of relaying and multi-user diversity; the stricter the constraints
on relay scheduling are, the less flexibility schedulers have to exploit
channel variation; and ) Thee standard contains a variety of parameters
for relaying configuration, but not all cases of interest are covered.Comment: 17 one-column pages, 9 figures, accepted for publication in IEEE ICC
2014 MW
Natural inflation in 5D warped backgrounds
In light of the five-year data from the Wilkinson Microwave Anisotropy Probe
(WMAP), we discuss models of inflation based on the pseudo Nambu-Goldstone
potential predicted in five-dimensional gauge theories for different
backgrounds: flat Minkowski, anti-de Sitter, and dilatonic spacetime. In this
framework, the inflaton potential is naturally flat due to shift symmetries and
the mass scales associated with it are related to 5D geometrical quantities.Comment: 10 pages, 8 figures; matches version to appear in Phys. Rev.
Baryon anticorrelations and the Pauli principle in PYTHIA
We present a computational investigation of a problem of hadron collisions
from recent years, that of baryon anticorrelations. This is an experimental
dearth of baryons near other baryons in phase space, not seen upon examining
numerical Monte Carlo simulations. We have addressed one of the best known
Monte Carlo codes, PYTHIA, to see what baryon (anti)correlations it produces,
where they are originated at the string-fragmentation level in the underlying
Lund model, and what simple modifications could lead to better agreement with
data. We propose two ad-hoc alterations of the fragmentation code, a
"one-baryon" and an "always-baryon" policies that qualitatively reproduce the
data behaviour, i.e anticorrelation, and suggest that lacking Pauli-principle
induced corrections at the quark level could be the culprit behind the current
disagreement between computations and experiment.Comment: 16 pages, 25 plot
Radiatively induced leptogenesis in a minimal seesaw model
We study the possibility that the baryon asymmetry of the universe is
generated in a minimal seesaw scenario where two right-handed Majorana
neutrinos with degenerate masses are added to the standard model particle
content. In the usual framework of thermal leptogenesis, a nonzero
asymmetry can be obtained through the mass splitting induced by the running of
the heavy Majorana neutrino masses from their degeneracy scale down to the
seesaw scale. Although, in the light of the present neutrino oscillation data,
the produced baryon asymmetry turns out to be smaller than the experimental
value, the present mechanism could be viable in simple extensions of the
standard model.Comment: 6 pages, 2 figures, uses RevTeX4, calculations improved, comments
adde
Magnetized strangelets at finite temperature
The main properties of magnetized strangelets, namely, their energy per
baryon, radius and electric charge, are studied. Temperature effects are also
taken into account in order to study their stability compared to the 56Fe
isotope and non-magnetized strangelets using the liquid drop model. Massive
quarks are considered with the aim to have a more realistic description for
strangelets in the astrophysical context and the environment of heavy ion
colliders, playing also an important role in the thermodynamical quantities of
the quark gas. It is concluded that the presence of a magnetic field tends to
stabilize more the strangelets, even when temperature effects are taken into
account. Magnetized strangelets in a paired superconductor phase (magnetized
color flavor locked phase) are also discussed. It is shown that they are more
stable than ordinary magnetized strangelets for typical gap values of the order
of O(100) MeV.Comment: 10 pages, 10 figures, discussion extended, new references adde
Model reduction for molecular diffusion in nanoporous media
Porous materials are widely used for applications in gas storage and
separation. The diffusive properties of a variety of gases in porous media can
be modeled using molecular dynamics simulations that can be computationally
demanding depending on the pore geometry, complexity and amount of gas
adsorbed. We explore a dimensionality reduction approach for estimating the
self-diffusion coefficient of gases in simple pores using Langevin dynamics,
such that the three-dimensional (3D) atomistic interactions that determine the
diffusion properties of realistic systems can be reduced to an effective
one-dimensional (1D) diffusion problem along the pore axis. We demonstrate the
approach by modeling the transport of nitrogen molecules in single-walled
carbon nanotubes of different radii, showing that 1D Langevin models can be
parametrized with a few single-particle 3D atomistic simulations. The reduced
1D model predicts accurate diffusion coefficients over a broad range of
temperatures and gas densities. Our work paves the way for studying the
diffusion process of more general porous materials as zeolites or
metal-organics frameworks with effective models of reduced complexity.Comment: 8 pages, 6 figure
Neutrinos and the matter-antimatter asymmetry in the Universe
The discovery of neutrino oscillations provides a solid evidence for nonzero
neutrino masses and leptonic mixing. The fact that neutrino masses are so tiny
constitutes a puzzling problem in particle physics. From the theoretical
viewpoint, the smallness of neutrino masses can be elegantly explained through
the seesaw mechanism. Another challenging issue for particle physics and
cosmology is the explanation of the matter-antimatter asymmetry observed in
Nature. Among the viable mechanisms, leptogenesis is a simple and
well-motivated framework. In this talk we briefly review these aspects, making
emphasis on the possibility of linking neutrino physics to the cosmological
baryon asymmetry originated from leptogenesis.Comment: 8 pages, 1 table, 1 figure; Based on talk given at the Symposium
STARS2011, 1 - 4 May 2011, Havana, Cuba; to be published in the Proceeding
A Dynamical Scheme for a Large CP-Violating Phase
A dynamical scheme where the third generation of quarks plays a distinctive
role is implemented. New interactions with a term induce the breaking
of the electroweak symmetry and the top-bottom mass splitting. A large
CP-violating phase naturally follows from the latter.Comment: 10 pages, LaTe
Aspects of thermal leptogenesis in braneworld cosmology
The mechanism of thermal leptogenesis is investigated in the high-energy
regime of braneworld cosmology. Within the simplest seesaw framework with
hierarchical heavy Majorana neutrinos, we study the implications of the
modified Friedmann equation on the realization of this mechanism. In contrast
with the usual leptogenesis scenario of standard cosmology, where low-energy
neutrino data favors a mildly strong washout regime, we find that leptogenesis
in the braneworld regime is successfully realized in a weak washout regime.
Furthermore, a quasi-degenerate light neutrino mass spectrum is found to be
compatible with this scenario. For an initially vanishing heavy Majorana
neutrino abundance, thermal leptogenesis in the brane requires the decaying
heavy Majorana neutrino mass to be M1 > 10^10 GeV and the fundamental
five-dimensional gravity scale 10^12 < M5 < 10^16 GeV, which corresponds to a
transition from brane to standard cosmology at temperatures 10^8 < Tt < 10^14
GeV.Comment: 7 pages, 3 figures, a few comments and references added. Final
version to appear in Phys. Rev.
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