1,192 research outputs found
Towards a Realistic Model of Higgsless Electroweak Symmetry Breaking
We present a 5D gauge theory in warped space based on a bulk SU(2)_L x
SU(2)_R x U(1)_(B-L) gauge group where the gauge symmetry is broken by boundary
conditions. The symmetry breaking pattern and the mass spectrum resembles that
in the standard model (SM). To leading order in the warp factor the rho
parameter and the coupling of the Z (or equivalently the S-parameter) are as in
the SM, while corrections are expected at the level of a percent. From the
AdS/CFT point of view the model presented here can be viewed as the AdS dual of
a (walking) technicolor-like theory, in the sense that it is the presence of
the IR brane itself that breaks electroweak symmetry, and not a localized Higgs
on the IR brane (which should be interpreted as a composite Higgs model). This
model predicts the lightest W, Z and photon resonances to be at around 1.2 TeV,
and no fundamental (or composite) Higgs particles.Comment: 10 pages. v2: refs adde
Impact of Traffic Sign Diversity on Autonomous Vehicles: A Literature Review
Traffic sign classification is indispensable for road traffic systems, including automated ones. There is a fundamental difference in the visual appearance of traffic signs from one country to another. Each dataset has its design standards and regulations based on shape, color, and information content, making implementing classification and recognition techniques more difficult. This paper aims to assess the influence of traffic sign diversity on autonomous vehicles (AVs) by reviewing several previous studies, comparing, summarizing their results, and focusing on classifying and detecting traffic sign datasets based on color, shape, and deep learning spaces using various methods and applications. Furthermore, it covers the main challenges facing road designers and planners considering changes to road safety infrastructure. It will be argued that compiling and standardizing a comprehensive global database of traffic signs is very difficult because it is costly and complex in application. However, it is still one of the possible solutions for the coming decades. Recommendations for future developments are also presented in this study
Ageing as a price of cooperation and complexity: Self-organization of complex systems causes the ageing of constituent networks
The analysis of network topology and dynamics is increasingly used for the description of the structure, function and evolution of complex systems. Here we summarize key aspects of the evolvability and robustness of the hierarchical network-set of macromolecules, cells, organisms, and ecosystems. Listing the costs and benefits of cooperation as a necessary behaviour to build this network hierarchy, we outline the major hypothesis of the paper: the emergence of hierarchical complexity needs cooperation leading to the ageing of the constituent networks. Local cooperation in a stable environment may lead to over-optimization developing an ‘always-old’ network, which ages slowly, and dies in an apoptosis-like process. Global cooperation by exploring a rapidly changing environment may cause an occasional over-perturbation exhausting system-resources, causing rapid degradation, ageing and death of an otherwise ‘forever-young’ network in a necrosis-like process. Giving a number of examples we explain how local and global cooperation can both evoke and help successful ageing. Finally, we show how various forms of cooperation and consequent ageing emerge as key elements in all major steps of evolution from the formation of protocells to the establishment of the globalized, modern human society. Thus, ageing emerges as a price of complexity, which is going hand-in-hand with cooperation enhancing each other in a successful community
Quasi-Localization of Gravity by Resonant Modes
We examine the behaviour of gravity in brane theories with extra dimensions
in a non-factorizable geometry. We find that for metrics which are
asymptotically flat far from the brane there is a resonant graviton mode at
zero energy. The presence of this resonance ensures quasi-localization of
gravity, whereby at intermediate scales the gravitational laws on the brane are
approximately four dimensional. However, for scales larger than the lifetime of
the graviton resonance the five dimensional laws of gravity will be reproduced
due to the decay of the four dimensional graviton. We also present a simple
classification of the possible types of effective gravity theories on the brane
that can appear for general non-factorizable background theories.Comment: 8 pages, 3 figures included. Requires JHEP.cls. Typos fixed, note and
references added. Added expression for width of resonanc
Oblique Corrections from Higgsless Models in Warped Space
We calculate the tree-level oblique corrections to electroweak precision
observables generated in higgless models of electroweak symmetry breaking with
a 5D SU(2)_L x SU(2)_R x U(1)_{B-L} gauge group on a warped background. In the
absence of brane induced kinetic terms (and equal left and right gauge
couplings) we find the S parameter to be ~1.15, while T,U~0, as in technicolor
theories. Planck brane induced kinetic terms and unequal left-right couplings
can lower S, however for sufficiently low values of S tree-level unitarity will
be lost. A kinetic term localized on the TeV brane for SU(2)_D will generically
increase S, however an induced kinetic term for U(1)_{B-L} on the TeV brane
will lower S. With an appropriate choice of the value of this induced kinetic
term S~0 can be achieved. In this case the mass of the lowest Z' mode will be
lowered to about ~300 GeV.Comment: 18 pages, LaTeX, 2 figures include
Curing the Ills of Higgsless Models: the S Parameter and Unitarity
We consider various constraints on Higgsless models of electroweak symmetry
breaking based on a bulk SU(2)_L x SU(2)_R x U(1)_{B-L} gauge group in warped
space. First we show that the S parameter which is positive if fermions are
localized on the Planck brane can be lowered (or made vanishing) by changing
the localization of the light fermions. If the wave function of the light
fermions is almost flat their coupling to the gauge boson KK modes will be
close to vanishing, and therefore contributions to the S parameter will be
suppressed. At the same time the experimental bounds on such Z' and W' gauge
bosons become very weak, and their masses can be lowered to make sure that
perturbative unitarity is not violated in this theory before reaching energies
of several TeV. The biggest difficulty of these models is to incorporate a
heavy top quark mass without violating any of the experimental bounds on bottom
quark gauge couplings. In the simplest models of fermion masses a sufficiently
heavy top quark also implies an unacceptably large correction to the Zb\bar{b}
vertex and a large splitting between the KK modes of the top and bottom quarks,
yielding large loop corrections to the T-parameter. We present possible
directions for model building where perhaps these constraints could be obeyed
as well.Comment: 21 pages, LaTeX, 5 figures. References and acknowledgements adde
A Rewriting-Logic-Based Technique for Modeling Thermal Systems
This paper presents a rewriting-logic-based modeling and analysis technique
for physical systems, with focus on thermal systems. The contributions of this
paper can be summarized as follows: (i) providing a framework for modeling and
executing physical systems, where both the physical components and their
physical interactions are treated as first-class citizens; (ii) showing how
heat transfer problems in thermal systems can be modeled in Real-Time Maude;
(iii) giving the implementation in Real-Time Maude of a basic numerical
technique for executing continuous behaviors in object-oriented hybrid systems;
and (iv) illustrating these techniques with a set of incremental case studies
using realistic physical parameters, with examples of simulation and model
checking analyses.Comment: In Proceedings RTRTS 2010, arXiv:1009.398
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