3,141 research outputs found

    Perspectives for t¯t cross-section measurement at ATLAS

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    The top-antitop pair production is one of the dominant processes in proton-proton collisions at multi-TeV energies. Here are presented the prospects for measuring the total top pair cross-section with the ATLAS detector using 200 pb−1 of data taken at 10TeV. The cross-section is determined in the single-lepton channel, and in the dilepton channel. Data-driven methods are studied to estimate the main background in both channels

    On localization and position operators in Moebius-covariant theories

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    Some years ago it was shown that, in some cases, a notion of locality can arise from the group of symmetry enjoyed by the theory, thus in an intrinsic way. In particular, when Moebius covariance is present, it is possible to associate some particular transformations to the Tomita Takesaki modular operator and conjugation of a specific interval of an abstract circle. In this context we propose a way to define an operator representing the coordinate conjugated with the modular transformations. Remarkably this coordinate turns out to be compatible with the abstract notion of locality. Finally a concrete example concerning a quantum particle on a line is also given.Comment: 19 pages, UTM 705, version to appear in RM

    Top physic results from ATLAS and CMS

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    In this paper a summary of some of the latest and most precise measurements in the top quark physics field performed by the ATLAS and CMS experiments are presented. These include the most precise measurements for t¯t and single top cross-section as well as for the top mass, but also various measurements of top production and decay. Higgs and New Physics searches in the top quark Sector are not reported here

    Stringent limits on top-quark compositeness from top anti-top production at the Tevatron and the LHC

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    If the top quark is a composite state made out of some constituents, its interaction with the gluon will be modified. We introduce the leading effective operators that contribute to the radius and anomalous magnetic moment of the top quark and study their effect on the cross section for top anti-top production at the Tevatron and the LHC. Current measurements of the cross sections set a stringent limit on the scale of compositeness. This limit is comparable to similar limits obtained for light quarks and those from electroweak precision measurements. It can be used to constrain the parameter space of some composite Higgs models.Comment: 18 pages, 9 figures, 1 table. Analysis extended to quadratic contributions of the effective couplings. Study of top spin polarizations added. New confidence intervals obtained. Figures of the bounds replaced. Bounds on C2 result weaker. Version accepted for publication in PR

    Bose-Einstein condensate and Spontaneous Breaking of Conformal Symmetry on Killing Horizons

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    Local scalar QFT (in Weyl algebraic approach) is constructed on degenerate semi-Riemannian manifolds corresponding to Killing horizons in spacetime. Covariance properties of the C∗C^*-algebra of observables with respect to the conformal group PSL(2,\bR) are studied.It is shown that, in addition to the state studied by Guido, Longo, Roberts and Verch for bifurcated Killing horizons, which is conformally invariant and KMS at Hawking temperature with respect to the Killing flow and defines a conformal net of von Neumann algebras, there is a further wide class of algebraic (coherent) states representing spontaneous breaking of PSL(2,\bR) symmetry. This class is labeled by functions in a suitable Hilbert space and their GNS representations enjoy remarkable properties. The states are non equivalent extremal KMS states at Hawking temperature with respect to the residual one-parameter subgroup of PSL(2,\bR) associated with the Killing flow. The KMS property is valid for the two local sub algebras of observables uniquely determined by covariance and invariance under the residual symmetry unitarily represented. These algebras rely on the physical region of the manifold corresponding to a Killing horizon cleaned up by removing the unphysical points at infinity (necessary to describe the whole PSL(2,\bR) action).Each of the found states can be interpreted as a different thermodynamic phase, containing Bose-Einstein condensate,for the considered quantum field. It is finally suggested that the found states could describe different black holes.Comment: 36 pages, 1 figure. Formula of condensate energy density modified. Accepted for pubblication in Journal of Mathematical Physic

    Evaluation of gas turbines as alternative energy production systems for a large cruise ship to meet new maritime regulations

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    As a consequence of the new and up-coming regulations imposed by the International Maritime Organization (IMO), polluting emissions produced by large ships are now under strict control. Moreover, specific areas called \u201cEmission Controlled Area\u201d (ECA), which request even lower pollutant emissions, will be extended. To face up to this issue, ships propelled by Internal Combustion Engines (ICEs) burning Heavy Fuel Oil (HFO) can be equipped with abatement devices such as scrubbers and Selective Catalytic Reactor systems. Along with these solutions, which seem to be the route ship-owners will prefer, other methods can be considered, such as the use of Marine Gas Oil (MGO): a more expensive fuel, but with lower sulphur content. The use of MGO allows users to consider a further and more drastic modification of the power system, namely the use of Gas Turbines (GTs) in place of ICEs. GTs, despite being less efficient, are much lighter, more compact, and can more easily reach low NOx emissions than ICEs. Even if these aspects are theoretically well known, there are still difficulties in finding studies reporting quantitative analysis (weight, dimensions, fuel consumption) that compare GT and ICE power systems employed on board. The present paper aims to provide these data by analyzing different solutions applied to a real case. Unlike other studies, the work is focused on a cruise ship rather than on a cargo ship, because a cruise ship's operation profile is more variable during the trip

    Black hole entropy from classical Liouville theory

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    In this article we compute the black hole entropy by finding a classical central charge of the Virasoro algebra of a Liouville theory using the Cardy formula. This is done by performing a dimensional reduction of the Einstein Hilbert action with the ansatz of spherical symmetry and writing the metric in conformally flat form. We obtain two coupled field equations. Using the near horizon approximation the field equation for the conformal factor decouples. The one concerning the conformal factor is a Liouville equation, it posses the symmetry induced by a Virasoro algebra. We argue that it describes the microstates of the black hole, namely the generators of this symmetry do not change the thermodynamical properties of the black hole.Comment: LaTeX, 11 pages, to appear on JHE

    Search for new physics with top quarks at the ATLAS experiment

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    With the proton-proton collision data collected during 2015 and 2016 at the centre-of-mass energy of 13 TeV, the ATLAS experiment is exceeding the sensitivity reached with the analysis of the 7 and 8 TeV data during LHC Run 1 for many New Physics scenarios involving top quarks and their heavy partners. In this contribution, some of the latest ATLAS results in searching for top-pair resonances, top and bottom vector-like quarks and four-top-quark events are shortly reviewed

    Rigorous steps towards holography in asymptotically flat spacetimes

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    Scalar QFT on the boundary ℑ+\Im^+ at null infinity of a general asymptotically flat 4D spacetime is constructed using the algebraic approach based on Weyl algebra associated to a BMS-invariant symplectic form. The constructed theory is invariant under a suitable unitary representation of the BMS group with manifest meaning when the fields are interpreted as suitable extensions to ℑ+\Im^+ of massless minimally coupled fields propagating in the bulk. The analysis of the found unitary BMS representation proves that such a field on ℑ+\Im^+ coincides with the natural wave function constructed out of the unitary BMS irreducible representation induced from the little group Δ\Delta, the semidirect product between SO(2) and the two dimensional translational group. The result proposes a natural criterion to solve the long standing problem of the topology of BMS group. Indeed the found natural correspondence of quantum field theories holds only if the BMS group is equipped with the nuclear topology rejecting instead the Hilbert one. Eventually some theorems towards a holographic description on ℑ+\Im^+ of QFT in the bulk are established at level of C∗C^* algebras of fields for strongly asymptotically predictable spacetimes. It is proved that preservation of a certain symplectic form implies the existence of an injective ∗*-homomorphism from the Weyl algebra of fields of the bulk into that associated with the boundary ℑ+\Im^+. Those results are, in particular, applied to 4D Minkowski spacetime where a nice interplay between Poincar\'e invariance in the bulk and BMS invariance on the boundary at ℑ+\Im^+ is established at level of QFT. It arises that the ∗*-homomorphism admits unitary implementation and Minkowski vacuum is mapped into the BMS invariant vacuum on ℑ+\Im^+.Comment: 62 pages, amslatex, xy package; revised section 2 and the conclusions; corrected some typos; added some references; accepted for pubblication on Rev. Math. Phy
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