11 research outputs found
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
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
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
W mass and Leptonic Z-decays in the NMSSM
We study a subset of electroweak-precision observables consisting of ,
, and
(characterizing leptonic
-decays) in the context of the NMSSM. After a brief review of common
MSSM-NMSSM effects, e.g. for ,
which has been little discussed, even in the MSSM), specific NMSSM scenarios
are studied, with the result that the NMSSM, considering existing constraints
on its spectrum, is essentially consistent with available measurements, given
the current accuracy.Comment: 25 pages, 12 figure
Constrained Supersymmetry after two years of LHC data: a global view with Fittino
We perform global fits to the parameters of the Constrained Minimal
Supersymmetric Standard Model (CMSSM) and to a variant with non-universal Higgs
masses (NUHM1). In addition to constraints from low-energy precision
observables and the cosmological dark matter density, we take into account the
LHC exclusions from searches in jets plus missing transverse energy signatures
with about 5\,fb of integrated luminosity. We also include the most
recent upper bound on the branching ratio from LHCb.
Furthermore, constraints from and implications for direct and indirect dark
matter searches are discussed. The best fit of the CMSSM prefers a light Higgs
boson just above the experimentally excluded mass. We find that the description
of the low-energy observables, in particular, and the
non-observation of SUSY at the LHC become more and more incompatible within the
CMSSM. A potential SM-like Higgs boson with mass around 126 GeV can barely be
accommodated. Values for just around the Standard
Model prediction are naturally expected in the best fit region. The
most-preferred region is not yet affected by limits on direct WIMP searches,
but the next generation of experiments will probe this region. Finally, we
discuss implications from fine-tuning for the best fit regions.Comment: 49 pages, 24 figures, to be submitted to JHE