3,208 research outputs found
Limits on Fourth Generation Fermions
We present recent results on searches for the fourth generation quarks
performed at the CMS and ATLAS experiments at LHC.Comment: Presented at the 2013 Flavor Physics and CP Violation (FPCP-2013),
Buzios, Rio de Janeiro, Brazil, May 19-24 2013, 8 pages, 7 figures, updated
reference
Search for Pair Production of Supersymmetric Top Quarks Mimicking Standard Model Top Event Signatures at CDF
We present results of the search for the super-symmetric partner of the top
quark, the stop quark, decaying to a b-quark and chargino with the subsequent
chargino decay into a neutralino, lepton and neutrino. Using the data sample
corresponding to 2.7 inv fb of integrated luminosity, collected with the CDF
Detector of the Tevatron collider, we reconstruct the stop mass of candidate
events and set 95% C. L. upper limits on masses of the stop quark, chargino and
neutralino and the branching ratio of chargino to neutralino+lepton+neutrino.Comment: ICHEP08 poster, Philadelphia, USA, July 2008. 3 pages, LaTeX, 3
figure
Top Quark Properties from Top Pair Events and Decays
Over a decade since the discovery of the top quark we are still trying to
unravel mysteries of the heaviest observed particle and learn more about its
nature. The continuously accumulating statistics of CDF and Dzero data provide
the means for measuring top quark properties with ever greater precision and
the opportunity to search for signs of new physics that could be manifested
through subtle deviations from the standard model in the production and decays
of top quarks. In the following we present a slice of the rich program in top
quark physics at the Fermilab Tevatron: measurements of the properties of top
quark decays and searches for unusual phenomena in events with pair produced
tops. In particular, we discuss the most recent and precise CDF and Dzero
measurements of the transverse polarization of W bosons from top decays,
branching ratios and searches for flavor-changing neutral current decays,
decays into charged Higgs and invisible decays. These analyses correspond to
integrated luminosities ranging from 0.9 to 2.7 inv. fb.Comment: Parallel talk at ICHEP08, Philadelphia, USA, July 2008. 4 pages,
LaTeX, 8 figure
Cutting and Pasting in the Torelli Group
We introduce machinery to allow ``cut-and-paste''-style inductive arguments
in the Torelli subgroup of the mapping class group. In the past these arguments
have been problematic because restricting the Torelli group to subsurfaces
gives different groups depending on how the subsurfaces are embedded. We define
a category \TSur whose objects are surfaces together with a decoration
restricting how they can be embedded into larger surfaces and whose morphisms
are embeddings which respect the decoration. There is a natural ``Torelli
functor'' on this category which extends the usual definition of the Torelli
group on a closed surface. Additionally, we prove an analogue of the Birman
exact sequence for the Torelli groups of surfaces with boundary and use the
action of the Torelli group on the complex of curves to find generators for the
Torelli group. For genus only twists about (certain) separating
curves and bounding pairs are needed, while for genus a new type of
generator (a ``commutator of a simply intersecting pair'') is needed. As a
special case, our methods provide a new, more conceptual proof of the classical
result of Birman-Powell which says that the Torelli group on a closed surface
is generated by twists about separating curves and bounding pairs.Comment: 33 pages, 8 figures, some stylistic improvements; to appear in
Geometry and Topolog
Cosmological Constraints from Primordial Black Holes
Primordial black holes may form in the early Universe, for example from the
collapse of large amplitude density perturbations predicted in some
inflationary models. Light black holes undergo Hawking evaporation, the energy
injection from which is constrained both at the epoch of nucleosynthesis and at
the present. The failure as yet to unambiguously detect primordial black holes
places important constraints. In this article, we are particularly concerned
with the dependence of these constraints on the model for the complete
cosmological history, from the time of formation to the present. Black holes
presently give the strongest constraint on the spectral index of density
perturbations, though this constraint does require to be constant over a
very wide range of scales.Comment: 8 pages LaTeX file, using elsart.sty, with three figures incorporated
using epsf. To appear, proceedings of DM98, Los Angeles (ed D Cline,
Elsevier
The rational cohomology of the mapping class group vanishes in its virtual cohomological dimension
Let Mod_g be the mapping class group of a genus g >= 2 surface. The group
Mod_g has virtual cohomological dimension 4g-5. In this note we use a theorem
of Broaddus and the combinatorics of chord diagrams to prove that
H^{4g-5}(Mod_g; Q) = 0.Comment: 4 pages. Final version, to appear in IMR
Superconformal symmetry and hyperKaehler manifolds with torsion
The geometry arising from Michelson & Strominger's study of N=4B
supersymmetric quantum mechanics with superconformal D(2,1;alpha)-symmetry is a
hyperKaehler manifold with torsion (HKT) together with a special homothety. It
is shown that different parameters alpha are related via changes in potentials
for the HKT target spaces. For alpha not 0 or -1, we describe how each such HKT
4m-manifold M is derived from a space N of dimension 4m-4 which is quaternionic
Kaehler with torsion and carries an Abelian instanton.Comment: 16 page
t-kvarkovski i elektroslabi rezultati na Tevatronu
Recent results from CDF and DĂ experiments on W and Z bosons and top quark properties are presented.Predstavljamo nove ishode CDF i DĂ mjerenja o svojstvima W i Z bosona te t-kvarka
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