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

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 $g \geq 1$ only twists about (certain) separating curves and bounding pairs are needed, while for genus $g=0$ 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 $n$ of density perturbations, though this constraint does require $n$ 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 DØ experiments on W and Z bosons and top quark properties are presented.Predstavljamo nove ishode CDF i DØ mjerenja o svojstvima W i Z bosona te t-kvarka

Probabilistic Surface Characterization for Safe Landing Hazard Detection and Avoidance (HDA)

Apparatuses, systems, computer programs and methods for performing hazard detection and avoidance for landing vehicles are provided. Hazard assessment takes into consideration the geometry of the lander. Safety probabilities are computed for a plurality of pixels in a digital elevation map. The safety probabilities are combined for pixels associated with one or more aim points and orientations. A worst case probability value is assigned to each of the one or more aim points and orientations