36 research outputs found
Electroweak parameters of the Z° resonance and the standard model
The four LEP experiments have each performed precision measurements of Z ° parameters. A method is described for combin- ing the results of the four experiments, which takes into account the experimental and theoretical systematic errors and their correlations. We apply this method to the 1989 and 1990 LEP data, corresponding to approximately 650 000 Z ° decays into hadrons and charged leptons, to obtain precision values for the Z ° parameters. We use these results to test the standard model and to constrain its parameters.Facultad de Ciencias Exacta
Electroweak parameters of the Z° resonance and the standard model
The four LEP experiments have each performed precision measurements of Z ° parameters. A method is described for combin- ing the results of the four experiments, which takes into account the experimental and theoretical systematic errors and their correlations. We apply this method to the 1989 and 1990 LEP data, corresponding to approximately 650 000 Z ° decays into hadrons and charged leptons, to obtain precision values for the Z ° parameters. We use these results to test the standard model and to constrain its parameters.Facultad de Ciencias Exacta
Electroweak Physics at LHC
The prospects for electroweak physics at the LHC are reviewed focusing mainly on precision studies. This includes projections for measurements of the effective Z pole weak mixing angle, of top quark, W boson, and Higgs scalar properties, and new physics searches
Re-evaluation of the LHC potential for the measurement of Mw
We present a study of the LHC sensitivity to the W boson mass based on
simulation studies. We find that both experimental and phenomenological sources
of systematic uncertainties can be strongly constrained with Z measurements:
the lineshape is robustly predicted, and its analysis provides an accurate
measurement of the detector resolution and absolute scale, while the
differential cross-section analysis absorbs most of the strong interaction
uncertainties. A sensitivity \delta Mw \sim 7 \MeV for each decay channel (W
--> e nu, W --> mu nu), and for an integrated luminosity of 10 fb-1, appears as
a reasonable goal
General analysis of signals with two leptons and missing energy at the Large Hadron Collider
A signal of two leptons and missing energy is challenging to analyze at the
Large Hadron Collider (LHC) since it offers only few kinematical handles. This
signature generally arises from pair production of heavy charged particles
which each decay into a lepton and a weakly interacting stable particle. Here
this class of processes is analyzed with minimal model assumptions by
considering all possible combinations of spin 0, 1/2 or 1, and of weak
iso-singlets, -doublets or -triplets for the new particles. Adding to existing
work on mass and spin measurements, two new variables for spin determination
and an asymmetry for the determination of the couplings of the new particles
are introduced. It is shown that these observables allow one to independently
determine the spin and the couplings of the new particles, except for a few
cases that turn out to be indistinguishable at the LHC. These findings are
corroborated by results of an alternative analysis strategy based on an
automated likelihood test.Comment: 18 pages, 3 figures, LaTe
The Algebra of Physical Observables in Nonlinearly Realized Gauge Theories
We classify the physical observables in spontaneously broken nonlinearly
realized gauge theories in the recently proposed loopwise expansion governed by
the Weak Power-Counting (WPC) and the Local Functional Equation. The latter
controls the non-trivial quantum deformation of the classical nonlinearly
realized gauge symmetry, to all orders in the loop expansion. The
Batalin-Vilkovisky (BV) formalism is used. We show that the dependence of the
vertex functional on the Goldstone fields is obtained via a canonical
transformation w.r.t. the BV bracket associated with the BRST symmetry of the
model. We also compare the WPC with strict power-counting renormalizability in
linearly realized gauge theories. In the case of the electroweak group we find
that the tree-level Weinberg relation still holds if power-counting
renormalizability is weakened to the WPC condition.Comment: 20 pages, 1 figur
Low-mass fermiophobic charged Higgs phenomenology in two-Higgs-doublet models
After the recent discovery of a Higgs-like boson, the possibility of an enlarged scalar sector arises as a natural question. Experimental searches for charged scalars have been already performed with negative results. We analyze the phenomenology associated with a fermiophobic charged Higgs (it does not couple to fermions at tree level), in two-Higgs-doublet models. All present experimental bounds are evaded trivially in this case, and one needs to consider other decay and production channels. We study the associated production of a charged Higgs with either a W or a neutral scalar boson, and the relevant decays for a light fermiophobic charged Higgs. The interesting features of this scenario should result encouraging for the LHC collaborations to perform searches for such a particle
T-parity, its problems and their solution
We point out a basic difficulty in the construction of little-Higgs models
with T-parity which is overlooked by large part of the present literature.
Almost all models proposed so far fail to achieve their goal: they either
suffer from sizable electroweak corrections or from a breakdown of collective
breaking. We provide a model building recipe to bypass the above problem and
apply it to build the simplest T-invariant extension of the Littlest Higgs. Our
model predicts additional T-odd pseudo-Goldstone bosons with weak scale masses.Comment: 25 pages, 2 appendice
Unnatural Origin of Fermion Masses for Technicolor
We explore the scenario in which the breaking of the electroweak symmetry is
due to the simultaneous presence and interplay of a dynamical sector and an
unnatural elementary Higgs. We introduce a low energy effective Lagrangian and
constrain the various couplings via direct search limits and electroweak and
flavor precision tests. We find that the model we study is a viable model of
dynamical breaking of the electroweak symmetry.Comment: 20 pages, 7 eps figure
Leptons in Holographic Composite Higgs Models with Non-Abelian Discrete Symmetries
We study leptons in holographic composite Higgs models, namely in models
possibly admitting a weakly coupled description in terms of five-dimensional
(5D) theories. We introduce two scenarios leading to Majorana or Dirac
neutrinos, based on the non-abelian discrete group which is
responsible for nearly tri-bimaximal lepton mixing. The smallness of neutrino
masses is naturally explained and normal/inverted mass ordering can be
accommodated. We analyze two specific 5D gauge-Higgs unification models in
warped space as concrete examples of our framework. Both models pass the
current bounds on Lepton Flavour Violation (LFV) processes. We pay special
attention to the effect of so called boundary kinetic terms that are the
dominant source of LFV. The model with Majorana neutrinos is compatible with a
Kaluza-Klein vector mass scale TeV, which is roughly the
lowest scale allowed by electroweak considerations. The model with Dirac
neutrinos, although not considerably constrained by LFV processes and data on
lepton mixing, suffers from a too large deviation of the neutrino coupling to
the boson from its Standard Model value, pushing TeV.Comment: 37 pages, 4 figures; v2: Note added in light of recent T2K and MINOS
results, figures updated with new limit from MEG, references added, various
minor improvements, matches JHEP published versio