178 research outputs found
Little Higgs Models: New Approaches to the Hierarchy Problem
In this note we present a review of the little Higgs models that stabilize
the electroweak by realizing the Standard Model Higgs as a pseudo-Goldstone
boson.Comment: Proceedings for ICHEP02, 3 pages, 2 figure
Measuring International Productivity: A Comparison of Sixteen Countries
During the last several decades productivity improvement measures have received increased recognition as important performance measures. This study analyzes and empirically estimates traditional productivity measures. Using data from sixteen countries, the results of this study indicate that the Hayes and Clark total factor productivity measure [2] is weakly associated with labor and investment in equipment, but more strongly associated with material productivity
A "Littlest Higgs" Model with Custodial SU(2) Symmetry
In this note, a ``littlest higgs'' model is presented which has an
approximate custodial SU(2) symmetry. The model is based on the coset space
. The light pseudo-goldstone bosons of the theory
include a {\it single} higgs doublet below a TeV and a set of three
triplets and an electroweak singlet in the TeV range. All of these scalars
obtain approximately custodial SU(2) preserving vacuum expectation values. This
model addresses a defect in the earlier moose
model, with the only extra complication being an extended top sector. Some of
the precision electroweak observables are computed and do not deviate
appreciably from Standard Model predictions. In an S-T oblique analysis, the
dominant non-Standard Model contributions are the extended top sector and higgs
doublet contributions. In conclusion, a wide range of higgs masses is allowed
in a large region of parameter space consistent with naturalness, where large
higgs masses requires some mild custodial SU(2) violation from the extended top
sector.Comment: 22 pages + 8 figures; JHEP style, added references and extra
discussion on size of T contributions, as well as some other minor
clarifications. Version to appear in JHE
Scalar Loops in Little Higgs Models
Loops of the scalar particles present in Little Higgs models generate
radiatively scalar operators that have been overlooked before in Little Higgs
analyses. We compute them using a technique, recently proposed to deal with
scalar fluctuations in non-linear sigma models, that greatly simplifies the
calculation. In particular models some of these operators are not induced by
loops of gauge bosons or fermions, are consistent with the Little Higgs
symmetries that protect the Higgs boson mass, and must also be included in the
Lagrangian. In general, scalar loops multiplicatively renormalize the
tree-level scalar operators, O_S -> O_S [1- N \Lambda^2/(4\pi f)^2] with large
N (e.g. N ~ 20 for the Littlest Higgs), suggesting a true UV cutoff \Lambda < 4
\pi f/\sqrt{N} significantly below the estimate 4\pi f of naive dimensional
analysis. This can have important implications for the phenomenology and
viability of Little Higgs models.Comment: 28 pages, LaTe
The littlest Higgs model and Higgs boson associated production with top quark pair at high energy linear collider
In the parameter space allowed by the electroweak precision measurement data,
we consider the contributions of the new particles predicted by the littlest
Higgs() model to the Higgs boson associated production with top quark pair
in the future high energy linear collider(). We find that the
contributions mainly come from the new gauge bosons and . For
reasonable values of the free parameters, the absolute value of the relative
correction parameter can be significanly large,
which might be observed in the future experiment with .Comment: latex files, 13 pages, 3 figure
Precision Electroweak Observables in the Minimal Moose Little Higgs Model
Little Higgs theories, in which the Higgs particle is realized as the
pseudo-Goldstone boson of an approximate global chiral symmetry have generated
much interest as possible alternatives to weak scale supersymmetry. In this
paper we analyze precision electroweak observables in the Minimal Moose model
and find that in order to be consistent with current experimental bounds, the
gauge structure of this theory needs to be modified. We then look for viable
regions of parameter space in the modified theory by calculating the various
contributions to the S and T parameters.Comment: v2: 17 pages, 9 figures. Typeset in JHEP style. Added a references
and two figures showing parameter space for each of two reference points.
Corrected typo
Studies of New Vector Resonances at the CLIC Multi-TeV e+e- Collider
Several models predict the existence of new vector resonances in the
multi-TeV region, which can be produced in high energy e+e- collisions in the
s-channel. In this paper we review the existing limits on the masses of these
resonances from LEP/SLC and TEVATRON data and from atomic parity violation in
some specific models. We study the potential of a multi-TeV e+e- collider, such
as CLIC, for the determination of their properties and nature.Comment: 17 pages, 16 EPS figures, uses JHEP3.cl
VEGAS as a Platform for Facile Directed Evolution in Mammalian Cells
Directed evolution, artificial selection toward designed objectives, is routinely used to develop new molecular tools and therapeutics. Successful directed molecular evolution campaigns repeatedly test diverse sequences with a designed selective pressure. Unicellular organisms and their viral pathogens are exceptional for this purpose and have been used for decades. However, many desirable targets of directed evolution perform poorly or unnaturally in unicellular backgrounds. Here, we present a system for facile directed evolution in mammalian cells. Using the RNA alphavirus Sindbis as a vector for heredity and diversity, we achieved 24-h selection cycles surpassing 10−3 mutations per base. Selection is achieved through genetically actuated sequences internal to the host cell, thus the system's name: viral evolution of genetically actuating sequences, or “VEGAS.” Using VEGAS, we evolve transcription factors, GPCRs, and allosteric nanobodies toward functional signaling endpoints each in less than 1 weeks’ time. © 2019 Elsevier Inc.The VEGAS system is a platform for directed evolution, a method for engineering DNA sequences, in mammalian cells. The system is highly mutagenic, facile, and self-contained, requiring no in vitro handling during evolution cycles. As a result, robust evolution campaigns can be run within the context of a mammalian cell signaling environment. We perform three such campaigns as a proof-of-concept: evolving a transcription factor, a G-protein coupled receptor, and llama-derived nanobodies toward specific in vivo activities. © 2019 Elsevier Inc
Erratum: VEGAS as a Platform for Facile Directed Evolution in Mammalian Cells (Cell (2019) 178(3) (748–761.e17), (S0092867419306221), (10.1016/j.cell.2019.05.051))
(Cell 178, 748–761.e1–e17; July 25, 2019) In our recent article reporting a platform for directed evolution in mammalian cells, we inadvertently failed to cite a paper that also reports a method for evolving biomolecules in mammalian cells (Berman et al., 2018). We have corrected the online version of our paper to cite this work, and we apologize for the omission. © 2019 Elsevier Inc
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