5,836 research outputs found
Searching for t-bar t Resonances at the Large Hadron Collider
Many new physics models predict resonances with masses in the TeV range which
decay into a pair of top quarks. With its large cross section, t-bar t
production at the Large Hadron Collider (LHC) offers an excellent opportunity
to search for such particles. We present a detailed study of the discovery
potential of the CERN Large Hadron Collider for Kaluza-Klein (KK) excitations
of the gluon in bulk Randall-Sundrum (RS) models in the t-bar t -> ell^+/- nu
b-bar bq-bar q' (ell=e, mu) final state. We utilize final states with one or
two tagged b-quarks, and two, three or four jets (including b-jets). Our
calculations take into account the finite resolution of detectors, the energy
loss due to b-quark decays, the expected reduced b-tagging efficiency at large
t-bar t invariant masses, and include the background originating from Wb-bar
b+jets, (Wb+W-bar b)+jets, W+jets, and single top + jets production. We derive
semi-realistic 5 sigma discovery limits for nine different KK gluon scenarios,
and compare them with those for KK gravitons, and a Z_H boson in the Littlest
Higgs model. We also analyze the capabilities of the LHC experiments to
differentiate between individual KK gluon models and measure the couplings of
KK gluons to quarks. We find that, for the parameters and models chosen, KK
gluons with masses up to about 4 TeV can be discovered at the LHC. The ability
of the LHC to discriminate between different bulk RS models, and to measure the
couplings of the KK gluons is found to be highly model dependent.Comment: revtex3, 27 pages, 5 tables, 6 figure
Probing Electroweak Top Quark Couplings at Hadron Colliders
We consider QCD t\bar{t}\gamma and t\bar{t}Z production at hadron colliders
as a tool to measure the tt\gamma and ttZ couplings. At the Tevatron it may be
possible to perform a first, albeit not very precise, test of the tt\gamma
vector and axial vector couplings in t\bar{t}\gamma production, provided that
more than 5 fb^{-1} of integrated luminosity are accumulated. The t\bar{t}Z
cross section at the Tevatron is too small to be observable. At the CERN Large
Hadron Collider (LHC) it will be possible to probe the tt\gamma couplings at
the few percent level, which approaches the precision which one hopes to
achieve with a next-generation e^+e^- linear collider. The LHC's capability of
associated QCD t\bar{t}V (V=\gamma, Z) production has the added advantage that
the tt\gamma and ttZ couplings are not entangled. For an integrated luminosity
of 300 fb^{-1}, the ttZ vector (axial vector) coupling can be determined with
an uncertainty of 45-85% (15-20%), whereas the dimension-five dipole form
factors can be measured with a precision of 50-55%. The achievable limits
improve typically by a factor of 2-3 for the luminosity-upgraded (3 ab^{-1})
LHC.Comment: Revtex3, 30 pages, 9 Figures, 6 Table
Improved Measurement of ttZ Couplings at the LHC
We consider QCD tt~Z production at the LHC with Z->\bar\nu\nu and
all-hadronic tt~ decays, i.e. pp -> p_T(miss)bb~+4 jets, as a tool to measure
ttZ couplings. This channel has a significantly larger cross section than those
where the Z boson decays leptonically. However, tt~, bb~+4 jet, tt~j and tt~jj
production give rise to potentially large backgrounds. We show that these
processes can be suppressed to an acceptable level with suitable cuts, and find
that adding the p_T(miss)bb~+4 jet channel to the final states used in previous
ttZ couplings analyses will improve the sensitivity by 10-60%. We also discuss
how the measurement of the ttZ couplings may constrain Little Higgs models.Comment: revtex4, 16 pages, 4 figures, 1 tabl
Vector Boson Pair Production in Hadronic Collisions at Order : Lepton Correlations and Anomalous Couplings
We present cross sections for production of electroweak vector boson pairs,
, and , in and collisions, at next-to-leading
order in . We treat the leptonic decays of the bosons in the
narrow-width approximation, but retain all spin information via decay angle
correlations. We also include the effects of and anomalous
couplings.Comment: 23 pages, 8 figures, 3 table
Probing Trilinear Gauge Boson Interactions via Single Electroweak Gauge Boson Production at the LHC
We analyze the potential of the CERN Large Hadron Collider (LHC) to study
anomalous trilinear vector-boson interactions W^+ W^- \gamma and W^+ W^- Z
through the single production of electroweak gauge bosons via the weak boson
fusion processes q q -> q q W (-> \ell^\pm \nu) and q q -> q q Z(-> \ell^+
\ell^-) with \ell = e or \mu. After a careful study of the standard model
backgrounds, we show that the single production of electroweak bosons at the
LHC can provide stringent tests on deviations of these vertices from the
standard model prediction. In particular, we show that single gauge boson
production exhibits a sensitivity to the couplings \Delta \kappa_{Z,\gamma}
similar to that attainable from the analysis of electroweak boson pair
production.Comment: 20 pages, 6 figure
On the dimensions of secant varieties of Segre-Veronese varieties
This paper explores the dimensions of higher secant varieties to
Segre-Veronese varieties. The main goal of this paper is to introduce two
different inductive techniques. These techniques enable one to reduce the
computation of the dimension of the secant variety in a high dimensional case
to the computation of the dimensions of secant varieties in low dimensional
cases. As an application of these inductive approaches, we will prove
non-defectivity of secant varieties of certain two-factor Segre-Veronese
varieties. We also use these methods to give a complete classification of
defective s-th Segre-Veronese varieties for small s. In the final section, we
propose a conjecture about defective two-factor Segre-Veronese varieties.Comment: Revised version. To appear in Annali di Matematica Pura e Applicat
On the Corrections to Dashen's Theorem
The electromagnetic corrections to the masses of the pseudoscalar mesons
and are considered. We calculate in chiral perturbation theory the
contributions which arise from resonances within a photon loop at order . Within this approach we find rather moderate deviations to Dashen's
theorem.Comment: 14 pages, sligthly enlarged version; a numerical error is corrected
and the embedding of the figures is improved. The complete paper, including
figures, is also available via anonymous ftp at
ftp://www-ttp.physik.uni-karlsruhe.de/ , or via www at
http://www-ttp.physik.uni-karlsruhe.de/cgi-bin/preprints/; to be published in
Phys.Rev.
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