Top-quark pair cross-section measurement in the lepton+jets channel

A measurement of the production cross-section for top quark pairs in pp collisions at sqrt{s} = 7 TeV is presented using data recorded with the ATLAS detector. Events are selected in the lepton+jets topology by requiring a single lepton (electron or muon), large missing transverse energy and at least three jets. No explicit identification of secondary vertices inside jets (b-tagging) is performed. A simple multivariate method using three kinematic variables is employed to extract the cross-section measurement.Comment: 4 pages, 4 figures, proceedings contribution for Moriond 2011 EW sessio

De Sitter quantum scalar field and horizon holography

We show explicitly that free quantum field theory in de Sitter background restricted on the cosmological horizon produces another quantum field theory unitarily equivalent with the original one. Symmetry properties descending from the dual theory are also remarked. In the restricted theory the thermal properties, known for de Sitter quantum field theory, can be proved straightforwardly.Comment: 14 pages, 1 figure, minor corrections, added reference

Global Existence of Solutions of the Semiclassical Einstein Equation for Cosmological Spacetimes

We study the solutions of the semiclassical Einstein equation in flat cosmological spacetimes driven by a massive conformally coupled scalar field. In particular, we show that it is possible to give initial conditions at finite time to get a state for the quantum field which gives finite expectation values for the stress-energy tensor. Furthermore, it is possible to control this expectation value by means of a global estimate on regular cosmological spacetimes. The obtained estimates permit to write a theorem about the existence and uniqueness of the local solutions encompassing both the spacetime metric and the matter field simultaneously. Finally, we show that one can always extend local solutions up to a point where the scale factor becomes singular or the Hubble function reaches a critical value $H_c = 180\pi/G$, which both correspond to a divergence of the scalar curvature, namely a spacetime singularity.Comment: 20 pages; corrected reference

Influence of quantum matter fluctuations on geodesic deviation

We study the passive influence of quantum matter fluctuations on the expansion parameter of a congruence of timelike geodesics in a semiclassical regime. In particular, we show that, the perturbations of this parameter can be considered to be elements of the algebra of matter fields at all perturbative order. Hence, once a quantum state for matter is chosen, it is possible to explicitly evaluate the behavior of geometric fluctuations. After introducing the formalism necessary to treat similar problems, in the last part of the paper, we estimate the approximated probability of having a geodesic collapse in a flat spacetime due to those fluctuations.Comment: 21 pages, published version, J. Phys. A: Math. Theor. 47 (2014) 37520

QFT holography near the horizon of Schwarzschild-like spacetimes

It is argued that free QFT can be defined on the event horizon of a Schwarzschild-like spacetime and that this theory is unitarily and algebraically equivalent to QFT in the bulk (near the horizon). Under that unitary equivalence the bulk hidden SL(2,R) symmetry found in a previous work becomes manifest on the event horizon, it being induced by a group of horizon diffeomorphisms. The class of generators of that group can be enlarged to include a full Virasoro algebra of fields which are defined on the event horizon. These generators have a quantum representation in QFT on the event horizon and thus in the bulk.Comment: 8 pages, 1 figure, latex 2e, Relevant references adde