235 research outputs found
Indirect Sensitivity to Heavy Z' Bosons at a Multi-TeV e+e- Collider
We compare the phenomenology of two models, the so-called minimal Z' and an
effective model for a SM-like Higgs realised as a composite state of a new
strong interaction, at a multi-TeV linear collider in the hypothesis that the
new physics is at a scale beyond the direct reach of the machine.Comment: 6 pages, 5 figures, to appear in the Proceedings of the International
Workshop on Future Linear Colliders LCWS201
Future Electron-Positron Colliders and the 4-Dimensional Composite Higgs Model
In this note we analyse the prospects of a future electron-positron collider
in testing a particular realisation of a composite Higgs model encompassing
partial compositeness, namely, the 4-Dimensional Composite Higgs Model. We
study the main Higgs production channels for three possible energy stages and
different luminosity options of such a machine and confront our results to the
expected experimental accuracies in the various Higgs decay channels accessible
herein and, for comparison, also at the Large Hadron Collider.Comment: 24 pages, 10 figures, minor corrections for publication in JHE
Top pair production at a future machine in a composite Higgs scenario
The top quark plays a central role in many New Physics scenarios and in
understanding the details of Electro-Weak Symmetry Breaking. In the short- and
mid-term future, top-quark studies will mainly be driven by the experiments at
the Large Hadron Collider. Exploration of top quarks will, however, be an
integral part of particle physics studies at any future facility and an collider will have a very comprehensive top-quark physics program. We
discuss the possibilities of testing NP in the top-quark sector within a
composite Higgs scenario through deviations from the Standard Model in top pair
production for different Centre-of-Mass energy options of a future
machine. In particular, we focus on precision studies of the top-quark sector
at a CM energy ranging from 370 GeV up to 3 TeV.Comment: 23 pages, 10 figures; v2: minor corrections, published on JHE
Improved analysis of the bounds from the electroweak precision tests on the 4-site model
We present a new complete analysis of the electroweak precision observables
within the recently proposed 4-site Higgsless model, which is based on the
SU(2)_L x SU(2)_1 x SU(2)_2 x U(1)_Y gauge symmetry and predicts six extra
gauge bosons, W_{1,2} and Z_{1,2}. Within the epsilon_i (i=1,2,3,b)
parametrization, we compute for the first time the EWPT bounds via a complete
numerical algorithm going beyond commonly used approximations. Both
epsilon_{1,3} impose strong constraints. Hence, it is mandatory to consider
them jointly when extracting EWPT bounds and to fully take in to account the
correlations among the electroweak precison measurements. The phenomenological
consequence is that the extra gauge bosons must be heavier than 250 GeV. Their
couplings to SM fermions, even if bounded, might be of the same order of
magnitude than the SM ones. In contrast to other Higgsless models, the 4-site
model is not fermiophobic. The new gauge bosons could thus be discovered in the
favoured Drell-Yan channel already during the present run of the LHC
experiment.Comment: Latex file, 35 pages, 10 figures, corrected typos, published versio
Exclusion and discovery via Drell-Yan in the 4DCHM
Searches for Z' bosons are most sensitive in the dilepton channels at hadron
colliders. Whilst finite width and interference effects do affect the
modifications the presence of BSM physics makes to Standard Model (SM)
contributions, generic searches are often designed to minimize these. The
experimental approach adopted works well in the case of popular models that
predict a single and narrow Z' boson allowing these effects to effectively be
neglected. Conversely, finite width and interference effects may have to be
taken into account in experimental analyses when such Z' states are wide or
where several states are predicted. We explore the consequences of these
effects in the 4-Dimensional Composite Higgs Model (4DCHM) which includes
multiple new Z' bosons and where the decays of these resonances to non-SM
fermions can result in large widths
Interference effects in heavy W'-boson searches at the LHC
Interference effects are widely neglected in searches for new physics. This
is the case in recent publications on searches for W'-bosons using leptonic
final states.
We examine the effects of interference on distributions frequently used to
determine mass limits for possible W'-bosons and show that there are important
qualitative effects on the behaviour of the new physics signal.
There are two main consequences. Firstly, exclusion limits where
interferences effects have not been considered are likely to have been
overestimated. Secondly, presenting experimental results as a function of a
transverse mass cut rather than in terms of the contribution of new physics to
the total cross-section would be more informative.Comment: 31 pages, 8 figures. Published versio
Drell-Yan production of multi Z'-bosons at the LHC within Non-Universal ED and 4D Composite Higgs Models
The Drell-Yan di-lepton production at hadron colliders is by far the
preferred channel to search for new heavy spin-1 particles. Traditionally, such
searches have exploited the Narrow Width Approximation (NWA) for the signal,
thereby neglecting the effect of the interference between the additional
Z'-bosons and the Standard Model Z and {\gamma}. Recently, it has been
established that both finite width and interference effects can be dealt with
in experimental searches while still retaining the model independent approach
ensured by the NWA. This assessment has been made for the case of popular
single Z'-boson models currently probed at the CERN Large Hadron Collider
(LHC). In this paper, we test the scope of the CERN machine in relation to the
above issues for some benchmark multi Z'-boson models. In particular, we
consider Non-Universal Extra Dimensional (NUED) scenarios and the 4-Dimensional
Composite Higgs Model (4DCHM), both predicting a multi-Z' peaking structure. We
conclude that in a variety of cases, specifically those in which the leptonic
decays modes of one or more of the heavy neutral gauge bosons are suppressed
and/or significant interference effects exist between these or with the
background, especially present when their decay widths are significant,
traditional search approaches based on the assumption of rather narrow and
isolated objects might require suitable modifications to extract the underlying
dynamics
From hidden symmetry to extra dimensions: a five dimensional formulation of the Degenerate BESS model
We consider the continuum limit of a moose model corresponding to a
generalization to N sites of the Degenerate BESS model. The five dimensional
formulation emerging in this limit is a realization of a RS1 type model with
SU(2)_L x SU(2)_R in the bulk, broken by boundary conditions and a vacuum
expectation value on the infrared brane. A low energy effective Lagrangian is
derived by means of the holographic technique and corresponding bounds on the
model parameters are obtained.Comment: Latex file, 40 pages and 5 figure
BSM Physics: What the Higgs Can Tell Us
This discovery of the Higgs boson last year has created new possibilities for
testing candidate theories for explaining physics beyond the Standard Model.
Here we explain the ways in which new physics can leave its marks in the
experimental Higgs data, and how we can use the data to constrain and compare
different models. In this proceedings paper we use two models, Minimal
Universal Extra Dimensions and the 4D Composite Higgs model, as examples to
demonstrate the technique.Comment: V2 corrected typo in author name. Submitted to the proceedings of the
41st ITEP Winter School, Mosco
The equivalence theorem for gauge boson scattering in a five-dimensional Standard Model
We present an equivalence theorem for the longitudinal components of the gauge bosons in a compactified five-dimensional extension of the Standard Model, whose spontaneous symmetry breaking is driven either by one Higgs in the bulk or by one on a brane or by both together. We also show some implications for the unitarity bounds on Higgs masses
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