Renormalization-group improved fully differential cross sections for top pair production

We extend approximate next-to-next-to-leading order results for top-pair production to include the semi-leptonic decays of top quarks in the narrow-width approximation. The new hard-scattering kernels are implemented in a fully differential parton-level Monte Carlo that allows for the study of any IR-safe observable constructed from the momenta of the decay products of the top. Our best predictions are given by approximate NNLO corrections in the production matched to a fixed order calculation with NLO corrections in both the production and decay subprocesses. Being fully differential enables us to make comparisons between approximate results derived via different (PIM and 1PI) kinematics for arbitrary distributions. These comparisons reveal that the renormalization-group framework, from which the approximate results are derived, is rather robust in the sense that applying a realistic error estimate allows us to obtain a reliable prediction with a reduced theoretical error for generic observables and analysis cuts

NNLL resummation for the associated production of a top pair with a heavy boson at the LHC

In this presentation we review recent results on the resummation of soft gluon emission corrections for the associated production of a top-quark pair with a heavy boson (Higgs/W/Z) at the Large Hadron Collider (LHC). We develop a parton level Monte Carlo based on a soft-gluon resummation formula valid up to next-to-next-to-leading logarithmic (NNLL) accuracy. With this tool we study the impact of the newly computed corrections to the total cross sections and some important differential distributions.Comment: 9 pages, 3 figures, 1 table. Proceedings of the 13th International Symposium on Radiative Corrections (RADCOR 2017), 24-29 September 2017, St. Gilgen, Austria. Based in part on arXiv:1611.00049 and arXiv:1702.0080

Master Integrals for double real radiation emission in heavy-to-light quark decay

We evaluate analytically the master integrals for double real radiation emission in the b --> u W* decay, where b and u are a massive and massless quark, respectively, while W* is an off-shell charged weak boson. Since the W boson can subsequently decay in a lepton anti-neutrino pair, the results of the present paper constitute a further step toward a fully analytic computation of differential distributions for the semileptonic decay of a b quark at NNLO in QCD. The latter partonic process plays a crucial role in the study of inclusive semileptonic charmless decays of B mesons. Our results are expressed in terms of multiple polylogarithms of maximum weight four.Comment: 21 pages, 6 figures, 2 table

Computation of H→ggH\to gg in FDH and DRED: renormalization, operator mixing, and explicit two-loop results

The $H\to gg$ amplitude relevant for Higgs production via gluon fusion is computed in the four-dimensional helicity scheme (FDH) and in dimensional reduction (DRED) at the two-loop level. The required renormalization is developed and described in detail, including the treatment of evanescent $\epsilon$-scalar contributions. In FDH and DRED there are additional dimension-5 operators generating the $H g g$ vertices, where $g$ can either be a gluon or an $\epsilon$-scalar. An appropriate operator basis is given and the operator mixing through renormalization is described. The results of the present paper provide building blocks for further computations, and they allow to complete the study of the infrared divergence structure of two-loop amplitudes in FDH and DRED

SCET approach to regularization-scheme dependence of QCD amplitudes

We investigate the regularization-scheme dependence of scattering amplitudes in massless QCD and find that the four-dimensional helicity scheme (FDH) and dimensional reduction (DRED) are consistent at least up to NNLO in the perturbative expansion if renormalization is done appropriately. Scheme dependence is shown to be deeply linked to the structure of UV and IR singularities. We use jet and soft functions defined in soft-collinear effective theory (SCET) to efficiently extract the relevant anomalous dimensions in the different schemes. This result allows us to construct transition rules for scattering amplitudes between different schemes (CDR, HV, FDH, DRED) up to NNLO in massless QCD. We also show by explicit calculation that the hard, soft and jet functions in SCET are regularization-scheme independent.Comment: 46 pages, 6 figure

La Geografía profesional en Francia : del geógrafo universitario al geógrafo profesional

A pesar que la componente práctica de la geografía es tan antigua como la misma disciplina, en los años que van del 1920 al 1960 la geografía se muestra especialmente como una disciplina científica, universitaria y escolar: los universitarios forman casi exclusivamente a profesores de historia y geografía. A partir de 1970, los universitarios, después de participar en trabajos de geografía aplicada, forman cada vez más a un mayor número de «profesionales», a fin de dar respuesta al número creciente de salidas profesionales que aparecen. Se crea de esta manera una variedad de formaciones diferentes, algunas de las cuales se analizan en este artículo. A pesar que las perspectivas son muy amplias, los geógrafos no han de olvidar la formación de los profesores de la enseñanza secundaria, sin los cuales la geografía sería impartida por los historiadores, que la considerarían como una disciplina secundaria en contraposición a la historia.Tot i que la component pràctica de la geografia és tan antiga com la mateixa disciplina, durant el període de temps que va del 1920 al 1960 la geografia es presenta sobretot com una disciplina científica, universitària i escolar: els universitaris formen, quasi exclusivament, professors d'història i de geografia. A partir de 1970, els universitaris, després de participar en treballs de geografia aplicada, formen cada vegada un nombre més elevat de «professionals», en consonància amb el nombre creixent de llocs de treball que apareixen. D'aquesta manera es crea una varietat de formacions diferents, algunes de les quals s'analitzen en aquest article. Malgrat que les perspectives són molt àmplies, els geògrafs no han d'oblidar la formació dels professors de l'ensenyament secundari, sense els quals la geografia seria impartida pels historiadors, que la considerarien com una disciplina secundària en contraposició a la història.Si l'origine des applications de la géographie est aussi ancienne que cette science, de 1920 à 1960 la géographie apparaît surtout comme une discipline scientifique, universitaire et scolaire: les universitaires forment presque uniquement des professeurs d'histoire et de geógraphie. Mais à partir de 1970, les universitaires, après avoir participé à des travaux de géographie appliquée, forment des «professionnels» dont le nombre s'accroît en fonction de débouchés de plus en plus larges. Pour les ouvrir, on adopte des types variés de formations dont quelques exemples sont analysés. Si les perspectives sont très larges, les géographes ne doivent pas négliger la formation des professeurs de l'enseignement du second degré, sans quoi la géographie sera enseignée par les seuls historiens qui la considèreront comme une discipline secondaire par rapport à l'histoire.If the applications of geography are as old as this science itself, from 1920 to 1960, geography appears mainly as a scientific, academic and scholar discipline: universities are training almost exclusively history and geography professors. But since 1970, academics, after taking part in applied geography works, are now training «professional» geographers whose number is growing steadily, owing to a wider range of jobs opportunities; new methods of training for these opportunities are analysed hereafter. If career prospects are important, academic geographers should not neglect the training of hight schools teachers; otherwise geography will be taught only by historians, who will consider it as secondary discipline compared with history

Approximate NNLO Predictions for the Stop-Pair Production Cross Section at the LHC

If the minimal supersymmetric standard model at scales of around 1 TeV is realized in nature, the total top-squark pair production cross section should be measurable at the CERN Large Hadron Collider. In this work we present precise predictions for this observable, which are based upon approximate NNLO formulas obtained using soft-collinear effective theory methods.Comment: 36 pages, 7 figures and 11 tables. Version published in JHEP 1307 (2013) 04

NNLL Momentum-Space Resummation for Stop-Pair Production at the LHC

If supersymmetry near the TeV scale is realized in Nature, the pair production of scalar top squarks is expected to be observable at the Large Hadron Collider. Recently, effective field-theory methods were employed to obtain approximate predictions for the cross section for this process, which include soft-gluon emission effects up to next-to-next-to-leading order (NNLO) in perturbation theory. In this work we employ the same techniques to resum soft-gluon emission effects to all orders in perturbation theory and with next-to-next-to-logarithmic (NNLL) accuracy. We analyze the effects of NNLL resummation on the stop-pair production cross section by obtaining NLO+NNLL predictions in pair invariant mass and one-particle inclusive kinematics. We compare the results of these calculations to the approximate NNLO predictions for the cross sections.Comment: 25 pages, 6 figure