155 research outputs found
Minimal Walking Technicolor: Set Up for Collider Physics
Different theoretical and phenomenological aspects of the Minimal and
Nonminimal Walking Technicolor theories have recently been studied. The goal
here is to make the models ready for collider phenomenology. We do this by
constructing the low energy effective theory containing scalars, pseudoscalars,
vector mesons and other fields predicted by the minimal walking theory. We
construct their self-interactions and interactions with standard model fields.
Using the Weinberg sum rules, opportunely modified to take into account the
walking behavior of the underlying gauge theory, we find interesting relations
for the spin-one spectrum. We derive the electroweak parameters using the newly
constructed effective theory and compare the results with the underlying gauge
theory. Our analysis is sufficiently general such that the resulting model can
be used to represent a generic walking technicolor theory not at odds with
precision data.Comment: 42 pages, 3 figures. RevTex forma
The Three Site Model at One-Loop
In this paper we compute the one-loop chiral logarithmic corrections to all
O(p^4) counterterms in the three site Higgsless model. The calculation is
performed using the background field method for both the chiral- and
gauge-fields, and using Landau gauge for the quantum fluctuations of the gauge
fields. The results agree with our previous calculations of the
chiral-logarithmic corrections to the S and T parameters in 't Hooft-Feynman
gauge. The work reported here includes a complete evaluation of all one-loop
divergences in an SU(2) x U(1) nonlinear sigma model, corresponding to an
electroweak effective Lagrangian in the absence of custodial symmetry.Comment: 40 pages, nine included eps figures. Minor corrections mad
The Status of Human Rights Protection in Europe: It’s complicated
The UK has voted to leave the European Union and Prime Minister Theresa May has expressed her aversion to the European Convention on Human Rights, but confusion abounds as to what the current architecture of Europe is, let alone what it might look like in the future. This article seeks to provide a comprehensive overview of the development of supranational human rights protections in Europe and the status of the current quest for greater integration. In particular, the stalled movement towards the accession of the EU to the ECHR is examined and likened to a riddle: to avoid subjecting Member States to conflicting obligations, the ECHR must be granted ultimate authority in the field of human rights, but without compromising the autonomy of EU law. The article concludes with a conversation with Dr Sonia Morano-Foadi, whose extensive research into the European human rights institutions enables her to shed some light on the likelihood of the accession riddle ever being solved and to provide a prognosis for European rights protections in the future
Top quark effects in composite vector pair production at the LHC
In the context of a strongly coupled Electroweak Symmetry Breaking, composite
light scalar singlet and composite triplet of heavy vectors may arise from an
unspecified strong dynamics and the interactions among themselves and with the
Standard Model gauge bosons and fermions can be described by a Effective Chiral Lagrangian. In this framework, the
production of the and final states at the LHC by
gluon fusion mechanism is studied in the region of parameter space consistent
with the unitarity constraints in the elastic channel of longitudinal gauge
boson scattering and in the inelastic scattering of two longitudinal Standard
Model gauge bosons into Standard Model fermions pairs. The expected rates of
same-sign di-lepton and tri-lepton events from the decay of the
final state are computed and their corresponding backgrounds are estimated. It
is of remarkable relevance that the final state can only be
produced at the LHC via gluon fusion mechanism since this state is absent in
the Drell-Yan process. It is also found that the final state
production cross section via gluon fusion mechanism is comparable with the
Drell-Yan production cross section. The comparison of the
and total cross sections will be crucial for
distinguishing the different models since the vector pair production is
sensitive to many couplings. This will also be useful to determine if the heavy
vectors are only composite vectors or are gauge vectors of a spontaneously
broken gauge symmetry.Comment: 18 pages, 5 tables, 6 figures. Missing figures added. Matches
published versio
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
Electroweak Corrections and Unitarity in Linear Moose Models
We calculate the form of the corrections to the electroweak interactions in
the class of Higgsless models which can be "deconstructed'' to a chain of SU(2)
gauge groups adjacent to a chain of U(1) gauge groups, and with the fermions
coupled to any single SU(2) group and to any single U(1) group along the chain.
The primary advantage of our technique is that the size of corrections to
electroweak processes can be directly related to the spectrum of vector bosons
("KK modes"). In Higgsless models, this spectrum is constrained by unitarity.
Our methods also allow for arbitrary background 5-D geometry, spatially
dependent gauge-couplings, and brane kinetic energy terms. We find that, due to
the size of corrections to electroweak processes in any unitary theory,
Higgsless models with localized fermions are disfavored by precision
electroweak data. Although we stress our results as they apply to continuum
Higgsless 5-D models, they apply to any linear moose model including those with
only a few extra vector bosons. Our calculations of electroweak corrections
also apply directly to the electroweak gauge sector of 5-D theories with a bulk
scalar Higgs boson; the constraints arising from unitarity do not apply in this
case.Comment: 50 pages, 11 eps figures, typos correcte
The S-parameter in Holographic Technicolor Models
We study the S parameter, considering especially its sign, in models of
electroweak symmetry breaking (EWSB) in extra dimensions, with fermions
localized near the UV brane. Such models are conjectured to be dual to 4D
strong dynamics triggering EWSB. The motivation for such a study is that a
negative value of S can significantly ameliorate the constraints from
electroweak precision data on these models, allowing lower mass scales (TeV or
below) for the new particles and leading to easier discovery at the LHC. We
first extend an earlier proof of S>0 for EWSB by boundary conditions in
arbitrary metric to the case of general kinetic functions for the gauge fields
or arbitrary kinetic mixing. We then consider EWSB in the bulk by a Higgs VEV
showing that S is positive for arbitrary metric and Higgs profile, assuming
that the effects from higher-dimensional operators in the 5D theory are
sub-leading and can therefore be neglected. For the specific case of AdS_5 with
a power law Higgs profile, we also show that S ~ + O(1), including effects of
possible kinetic mixing from higher-dimensional operator (of NDA size) in the
theory. Therefore, our work strongly suggests that S is positive in
calculable models in extra dimensions.Comment: 21 pages, 2 figures. v2: references adde
Invisible Higgs and Dark Matter
We investigate the possibility that a massive weakly interacting fermion
simultaneously provides for a dominant component of the dark matter relic
density and an invisible decay width of the Higgs boson at the LHC. As a
concrete model realizing such dynamics we consider the minimal walking
technicolor, although our results apply more generally. Taking into account the
constraints from the electroweak precision measurements and current direct
searches for dark matter particles, we find that such scenario is heavily
constrained, and large portions of the parameter space are excluded.Comment: arXiv admin note: text overlap with arXiv:0912.229
Generalized Weinberg Sum Rules in Deconstructed QCD
Recently, Son and Stephanov have considered an "open moose" as a possible
dual model of a QCD-like theory of chiral symmetry breaking. In this note we
demonstrate that although the Weinberg sum rules are satisfied in any such
model, the relevant sums converge very slowly and in a manner unlike QCD.
Further, we show that such a model satisfies a set of generalized sum rules.
These sum rules can be understood by looking at the operator product expansion
for the correlation function of chiral currents, and correspond to the absence
of low-dimension gauge-invariant chiral symmetry breaking condensates. These
results imply that, regardless of the couplings and F-constants chosen, the
open moose is not the dual of any QCD-like theory of chiral symmetry breaking.
We also show that the generalized sum rules can be "solved", leading to a
compact expression for the difference of vector- and axial-current correlation
functions. This expression allows for a simple formula for the S parameter
(L_10), which implies that S is always positive and of order one in any
(unitary) open linear moose model. Therefore the S parameter is positive and
order one in any "Higgsless model" based on the continuum limit of a linear
moose regardless of the warping or position-dependent gauge-coupling chosen.Comment: 12 pages, 5 eps figures; reference to overlapping work adde
- …