80 research outputs found
Anomalous quartic WWgammagamma and WWZgamma couplings through WWZ production in gamma gamma colliders
We find 95% confidence level limits on the anomalous coupling parameters
, and with an integrated luminosity of and and 1.5 TeV energies. We take into account incoming beam
polarizations and also the final state polarizations of the gauge bosons in the
cross-section calculations to improve the bounds. We show that polarization
leads to a significant amount of improvement in the sensitivity limits.Comment: 16 pages, 6 figures, 3 table
Single-top production at future ep colliders
The production of top quarks in single mode at future ep colliders is
studied, the attention being mainly focused to the case of the proposed LEPXLHC
collider. We are motivated to reanalyse such a process following the discovery
of the top quark at Fermilab. Thanks to the measurement of its mass one is now
able to establish more accurately the relevance of single top production for
itself and for many other processes to which it may act as a background. In
addition, the recent improvement of our knowledge of the quark and gluon
dynamics inside the proton now allows one to pin down the dependence of single
top production on the partonic structure functions. Both the leptonic and
hadronic decay channels of the top quark are studied and compared to the yield
of the corresponding irreducible background in presence of b-taggingComment: 28 pages, latex, epsfig, 10 postscript figures, complete paper
available at ftp://axpa.hep.phy.cam.ac.uk/moretti/cavendish_9704 and at
http://www.hep.phy.cam.ac.uk/theory/papers
Constraints on Quartic Vector-Boson Interactions from Z Physics
We obtain the constraints on possible anomalous quartic vector-boson vertices
arising from the precision measurements at the pole. In the framework of
chiral Lagrangians, we examine all effective operators
of order that lead to four-gauge-boson interactions but do not induce
anomalous trilinear vertices. We constrain the anomalous quartic interactions
by evaluating their one-loop corrections to the pole physics. Our analysis
is performed in a generic gauge and it shows that only the operators
that break the custodial symmetry get limits close to the theoretical
expectations. Our results also indicate that these anomalous couplings are
already out of reach of the Next Linear Collider, while the Large
Hadron Collider could be able to further extend the bounds on some of these
couplings.Comment: 16 pages, 1 Postscript figures, uses RevTex and eps.st
Probing Anomalous Quartic Couplings in e-gamma and gamma-gamma Colliders
We analyze the potential of the e+e- Linear Colliders, operating in the
e-gamma and gamma-gamma modes, to probe anomalous quartic vector--boson
interactions through the multiple production of W's and Z's. We examine all
chiral operators of order p^4 that lead to new
four--gauge--boson interactions but do not alter trilinear vertices. We show
that the e-gamma and gamma-gamma modes are able not only to establish the
existence of a strongly interacting symmetry breaking sector but also to probe
for anomalous quartic couplings of the order of 10^{-2} at 90% CL. Moreover,
the information gathered in the e-gamma mode can be used to reduced the
ambiguities of the e+e- mode.Comment: Revtex, 18 pages, 6 figure
Tests of Anomalous Quartic Couplings at the NLC
We analyze the potential of the Next Linear Collider to study
anomalous quartic vector-boson interactions through the processes and . In the framework of chiral
Lagrangians, we examine all effective operators of order that lead to
four-gauge-boson interactions but do not induce anomalous trilinear vertices.
In our analysis, we take into account the decay of the vector bosons to
fermions and evaluate the efficiency in their reconstruction. We obtain the
bounds that can be placed on the anomalous quartic interactions and we study
the strategies to distinguish the possible couplings.Comment: 18 pages, ReVTeX, 3 figures, typos corrected and references adde
Anomalous Couplings in e^+ e^- --> W^+ W^- gamma at LEP2 and NLC
We present sensitivity limits on the coefficients of a dimension-6 effective
Lagrangian that parametrizes the possible effects of new physics beyond the
Standard Model. Our results are based on the study of the process at LEP2 and NLC energies. In our calculations, we include all
the new anomalous interactions, involving vector and Higgs bosons, and take
into account the Standard Model irreducible background. We analyse the impact
of these new interactions on the total cross section, including the effects of
the initial electron and final W polarizations. We then focus on the operators
that will not be constrained by the process, obtaining
limits based on the photon energy distribution.Comment: 20 pages + 12 figures, RevTex. Version to be published in Phys. Rev.
ERK2 Suppresses Self-Renewal Capacity of Embryonic Stem Cells, but Is Not Required for Multi-Lineage Commitment
Activation of the FGF-ERK pathway is necessary for naïve mouse embryonic stem (ES) cells to exit self-renewal and commit to early differentiated lineages. Here we show that genetic ablation of Erk2, the predominant ERK isozyme expressed in ES cells, results in hyper-phosphorylation of ERK1, but an overall decrease in total ERK activity as judged by substrate phosphorylation and immediate-early gene (IEG) induction. Normal induction of this subset of canonical ERK targets, as well as p90RSK phosphorylation, was rescued by transgenic expression of either ERK1 or ERK2 indicating a degree of functional redundancy. In contrast to previously published work, Erk2-null ES cells exhibited no detectable defect in lineage specification to any of the three germ layers when induced to differentiate in either embryoid bodies or in defined neural induction conditions. However, under self-renewing conditions Erk2-null ES cells express increased levels of the pluripotency-associated transcripts, Nanog and Tbx3, a decrease in Nanog-GFP heterogeneity, and exhibit enhanced self-renewal in colony forming assays. Transgenic add-back of ERK2 is capable of restoring normal pluripotent gene expression and self-renewal capacity. We show that ERK2 contributes to the destabilization of ES cell self-renewal by reducing expression of pluripotency genes, such as Nanog, but is not specifically required for the early stages of germ layer specification
Intermediate mass standard model Higgs boson at the proposed CERN LEPLHC collider
The production of the \sm\ Higgs with intermediate mass at the
proposed CERN LEPLHC collider in , and
events is studied. This is done for all
possible (massive) flavours of the quarks and using photons generated
via Compton back--scattering of laser light. We study signatures in which the
Higgs decays to --pairs and the electroweak vector bosons and
decay either hadronically or leptonically. All possible backgrounds to
these signals are also computed. Flavour identification on --jets is
assumed. Explicit formulae for the helicity amplitudes of the above processes
are given.Comment: 31 pages, Latex, 8 figures uuencoded, revised version, significant
changes in the discussion of the results, in tables and figure
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