Constraining heavy colored resonances from top-antitop quark events

Recent measurements of the top quark charge asymmetry at Tevatron disfavor the existence of flavor universal axigluons and colorons at 2 sigmas. In this letter we explore the possibility to reconcile the data with these models and use the charge asymmetry and the invariant mass distribution of top-antitop quark pair events to constrain the mass and couplings of massive color-octet gauge bosons decaying to top quarks.Comment: 4 pages, 4 figures. References added, final version to appear in Phys.Rev.

Low energy Yukawa input parameters for Yukawa coupling Unification

I make a short review of the most recent determinations of the quark masses and run them to the $M_Z$ energy scale.Comment: 9 pages, LaTeX, talk given at the International Workshop on Elementary Particle Physics: Present and Future, June 5 to 9, 1995, Valencia, Spain. To appear in the Proceedings, World Scientific. Uses sprocl.st

Massive color-octet bosons and the charge asymmetries of top quarks at hadron colliders

Several models predict the existence of heavy colored resonances decaying to top quarks in the TeV energy range that might be discovered at the LHC. In some of those models, moreover, a sizable charge asymmetry of top versus antitop quarks might be generated. The detection of these exotic resonances, however, requires selecting data samples where the top and the antitop quarks are highly boosted, which is experimentally very challenging. We asses that the measurement of the top quark charge asymmetry at the LHC is very sensitive to the existence of excited states of the gluon with axial-vector couplings to quarks. We use a toy model with general flavour independent couplings, and show that a signal can be detected with relatively not too energetic top and antitop quarks. We also compare the results with the asymmetry predicted by QCD, and show that its highest statistical significance is achieved with data samples of top-antitop quark pairs of low invariant masses.Comment: 20 page

Top Quarks, Axigluons and Charge Asymmetries at Hadron Colliders

Axigluons are colored heavy neutral gauge boson that couple to quarks through an axial vector current and the same strong coupling as gluons. The most important model-independent manifestation of axigluons is the generation of a forward--backward asymmetry in top-antitop quark production at $p\bar{p}$ collisions which originates from the charge asymmetry. We update our previous analysis for the inclusive QCD induced forward--backward asymmetry and define a new observable which is more sensitive to the effect than the forward--backward asymmetry. Furthermore, we find a lower limit of 1.2 TeV at 90% C.L. on the axigluon mass from recent measurements of the asymmetry at Tevatron. Also at LHC, the charge asymmetry is sizable in suitably selected samples. We evaluate this asymmetry in the central region for different selection cuts and show that, like at Tevatron, the charge asymmetry can probe larger values of the axigluon mass than the dijet mass distribution.Comment: 13 pages, 9 figure

Multigluonic scattering amplitudes of heavy quarks

We consider heavy quark and antiquark off-shell spinorial currents with emission of an arbitrary number of gluons of positive helicity. From this results we calculate the corresponding on-shell scattering amplitude and the quark-antiquark vector current. Then, we show that in the heavy top quark effective theory the holomorfic component of the Higgs -> q (q) over tilde + n-gluon amplitude vanish for helicity conserving configurations

Radiative return at NLO and the measurement of the hadronic cross-section

The measurement of the hadronic cross-section in e+e− annihilation at high luminosity factories using the radiative return method is motivated and discussed. A Monte Carlo generator which simulates the radiative process e+e−→γ+hadrons at the next-to-leading order accuracy is presented. The analysis is then extended to the description of events with hard photons radiated at very small angle

Asymptotic expansions through the loop-tree duality

First results towards a general method for asymptotic expansions of Feynman amplitudes in the loop-tree duality (LTD) formalism are presented. The asymptotic expansion takes place at integrand-level in the Euclidean space of the loop three-momentum, where the hierarchies among internal and external scales are well-defined. Additionally, the UV behaviour of the individual contributions to the asymptotic expansion emerges only in the first terms of the expansion and is renormalized locally in four space-time dimensions. These two properties represent an advantage over the method of Expansion by Regions (EbR). We explore different approaches in different kinematical limits, and derive general guidelines with several benchmark examples.Comment: 23 pages, 7 figure

Características morfológicas y sedimentarias de la playa artificial de Poniente (Gijón. Asturias). Evolución 1995-2004

La playa arenosa de Poniente, construida como una playa confinada entre diques artificiales, ha evolucionado como una playa reflejante, caracterizada por el desarrollo de una barra supramareal en los 2/3 centrales de la playa y un frente inter-supraniareal de cierta pendiente, suavizado hacia los extremos laterales, el occidental más protegido. Asimismo, los vientos del NE y NO han generado campos de dunas en ambos extremos de la playa, disminuyendo el espacio original a medida que el oleaje ha removilizado las áreas más interna