823 research outputs found
Unitarity constraints on top quark signatures of Higgsless models
We use conditions for unitarity cancellations to constrain the couplings of
the top and bottom quarks to Kaluza-Klein modes in Higgsless models of
electroweak symmetry breaking. An example for the mass spectrum of quark
resonances in a theory space model is given and the implications for the
collider phenomenology in the top sector are discussed, comparing to signatures
of Little Higgs and strong electroweak symmetry breaking models.Comment: 19 pages LaTeX, 4 figures; published versio
Off-the-Wall Higgs in the Universal Randall-Sundrum Model
We outline a consistent Randall-Sundrum (RS) framework in which a fundamental
5-dimensional Higgs doublet induces electroweak symmetry breaking (EWSB). In
this framework of a warped Universal Extra Dimension, the lightest Kaluza-Klein
(KK) mode of the bulk Higgs is tachyonic leading to a vacuum expectation value
(vev) at the TeV scale. The consistency of this picture imposes a set of
constraints on the parameters in the Higgs sector. A novel feature of our
scenario is the emergence of an adjustable bulk profile for the Higgs vev. We
also find a tower of non-tachyonic Higgs KK modes at the weak scale. We
consider an interesting implementation of this ``Off-the-Wall Higgs'' mechanism
where the 5-dimensional curvature-scalar coupling alone generates the tachyonic
mode responsible for EWSB. In this case, additional relations among the
parameters of the Higgs and gravitational sectors are established. We discuss
the experimental signatures of the bulk Higgs in general, and those of the
``Gravity-Induced'' EWSB in particular.Comment: 27 pages, 4 figure
Quark mixings and flavor changing interactions with singlet quarks
Aspects of the quark mixings and flavor changing interactions are
investigated in electroweak models with singlet quarks. The effects on the
ordinary quark mixing are determined in terms of the quark masses and the
parameters describing the mixing between the ordinary quarks q and the singlet
quarks Q (q-Q mixing). Some salient features arise in the flavor changing
interactions through the q-Q mixing. The unitarity of the
Cabibbo-Kobayashi-Maskawa (CKM) matrix within the ordinary quark sector is
violated, and the flavor changing neutral currents (FCNC's) appear both in the
gauge and scalar couplings. The flavor changing interactions are calculated
appropriately in terms of the q-Q mixing parameters and the quark masses, which
really exhibit specific flavor structures. It is found that there are
reasonable ranges of the model parameters to reproduce the ordinary quark mass
hierarchy and the actual CKM structure even in the presence of q-Q mixing. Some
phenomenological effects of the singlet quarks are also discussed. In
particular, the scalar FCNC's may be more important in some cases, if the
singlet quarks as well as the extra scalar particles from the singlet Higgs
fields have masses 100 GeV -- 1 TeV.Comment: 32 pages, 7 figures, added reference
Event-triggered distributed Hâ state estimation with packet dropouts through sensor networks
This study is concerned with the event-triggered distributed Hâ state estimation problem for a class of discrete-time stochastic non-linear systems with packet dropouts in a sensor network. An event-triggered communication mechanism is adopted over the sensor network with hope to reduce the communication burden and the energy consumption, where the measurements on each sensor are transmitted only when a certain triggering condition is violated. Furthermore, a novel distributed state estimator is designed where the available innovations are not only from the individual sensor, but also from its neighbouring ones according to the given topology. The purpose of the problem under consideration is to design a set of distributed state estimators such that the dynamics of estimation errors is exponentially mean-square stable and also the prespecified Hâ disturbance rejection attenuation level is guaranteed. By utilising the property of the Kronecker product and the stochastic analysis approaches, sufficient conditions are established under which the addressed state estimation problem is recast as a convex optimisation one that can be easily solved via available software packages. Finally, a simulation example is utilised to illustrate the usefulness of the proposed design scheme of event-triggered distributed state estimators.This work was supported in part by Royal Society of the UK, the National Natural Science Foundation of China under Grants 61329301, 61203139, 61473076, 61374127 and 61422301, the Shanghai Rising-Star Program of China under Grant 13QA1400100, the ShuGuang project of Shanghai Municipal Education Commission and Shanghai Education Development Foundation under Grant 13SG34, the Fundamental Research Funds for the Central Universities, DHU Distinguished Young Professor Program, and the Alexander von Humboldt Foundation of Germany
A global pact for the environment: Conceptual foundations
This article introduces the conceptual foundations of the initiative towards the adoption of a Global Pact for the Environment. It first situates the search for a global framework instrument on environmental protection in a long-term perspective and then discusses the main reasons why it is needed. Against this background, the article presents the current expression of this much broader trend, in the form of the initiative for a Global Pact for the Environment and the momentum it has generated in policy circles, first and foremost at the level of the United Nations General Assembly
A clean signal for a top-like isosinglet fermion at the Large Hadron Collider
We predict a clean signal at the Large Hadron Collider (=14 TeV for
a scenario where there is a top-like, charge +2/3 vectorlike isosinglet
fermion. Such a quark, via mixing with the standard model top, can undergo
decays via both flavour-changing Z-boson coupling and flavour-changing Yukawa
interactions. We concentrate on the latter channel, and study the situation
where, following its pair-production, the heavy quark pair gives rise to two
tops and two Higgs boson. We show that the case where each Higgs decays in the
channel, there can be a rather distinct and background-free signal
that can unveil the existence of the vectorlike isosinglet quark of this kind.Comment: 14 pages, 5 figures, 4 table
Brane-localized Kinetic Terms in the Randall-Sundrum Model
We examine the effects of boundary kinetic terms in the Randall-Sundrum model
with gauge fields in the bulk. We derive the resulting gauge Kaluza-Klein (KK)
state wavefunctions and their corresponding masses, as well as the KK gauge
field couplings to boundary fermions, and find that they are modified in the
presence of the boundary terms. In particular, for natural choices of the
parameters, these fermionic couplings can be substantially suppressed compared
to those in the conventional Randall-Sundrum scenario. This results in a
significant relaxation of the bound on the lightest gauge KK mass obtained from
precision electroweak data; we demonstrate that this bound can be as low as a
few hundred GeV. Due to the relationship between the lightest gauge KK state
and the electroweak scale in this model, this weakened constraint allows for
the electroweak scale to be near a TeV in this minimal extension of the
Randall-Sundrum model with bulk gauge fields, as opposed to the conventional
scenario.Comment: 24 pages, 8 figures, LaTex. Discussion and figure added addressing
the effects of this analysis on the hierarch
Signals from extra dimensions decoupled from the compactification scale
Multilocalization provides a simple way of decoupling the mass scale of new
physics from the compactification scale of extra dimensions. It naturally
appears, for example, when localization of fermion zero modes is used to
explain the observed fermion spectrum, leaving low energy remnants of the
geometrical origin of the fermion mass hierarchy. We study the phenomenology of
the simplest five dimensional model with order one Yukawa couplings reproducing
the standard fermion masses and mixing angles and with a light Kaluza-Klein
quark Q_{2/3} saturating experimental limits on V_{tb} and m_Q, and then with
observable new effects at Tevatron.Comment: 18 pages, 7 figs; v2 reference and comments added to match the
published version. A discussion of the limits from precision electroweak data
is included. Conclusions are unchange
Tree-level FCNC in the B system: from CP asymmetries to rare decays
Tree-level Flavor-Changing Neutral Currents (FCNC) are characteristic of
models with extra vector-like quarks. These new couplings can strongly modify
the B^0 CP asymmetries without conflicting with low--energy constraints. In the
light of a low CP asymmetry in B --> J/\psi K_{S}, we discuss the implications
of these contributions. We find that even these low values can be easily
accommodated in these models. Furthermore, we show that the new data from B
factories tend to favor an O(20) enhancement of the b --> d l \bar{l}
transition over the SM expectation.Comment: 5 pages, 4 figures. Accepted version in PRD. Updated analysis with
the new results from BaBar and BELLE. Figures enlarged, small typos
corrected. Conclusions essentially unchange
Effective Lagrangian approach to neutrinoless double beta decay and neutrino masses
Neutrinoless double beta () decay can in general produce
electrons of either chirality, in contrast with the minimal Standard Model (SM)
extension with only the addition of the Weinberg operator, which predicts two
left-handed electrons in the final state. We classify the lepton number
violating (LNV) effective operators with two leptons of either chirality but no
quarks, ordered according to the magnitude of their contribution to \znbb
decay. We point out that, for each of the three chirality assignments, and , there is only one LNV operator of the corresponding type
to lowest order, and these have dimensions 5, 7 and 9, respectively. Neutrino
masses are always induced by these extra operators but can be delayed to one or
two loops, depending on the number of RH leptons entering in the operator.
Then, the comparison of the decay rate and neutrino masses
should indicate the effective scenario at work, which confronted with the LHC
searches should also eventually decide on the specific model elected by nature.
We also list the SM additions generating these operators upon integration of
the heavy modes, and discuss simple realistic examples of renormalizable
theories for each case.Comment: Accepted for publication. Few misprints corrected and new references
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