2,122 research outputs found

    Virtual amplitudes and threshold behaviour of hadronic top-quark pair-production cross sections

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    We present the two-loop virtual amplitudes for the production of a top-quark pair in gluon fusion. The evaluation method is based on a numerical solution of differential equations for master integrals in function of the quark velocity and scattering angle starting from a boundary at high-energy. The results are given for the renormalized infrared finite remainders on a large grid and have recently been used in the calculation of the total cross sections at the next-to-next-to-leading order. For convenience, we also give the known results for the quark annihilation case on the same grid. Outside of the kinematical range covered by the grid, we provide threshold and high-energy expansions

    The soft function for color octet production at threshold

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    We evaluate the next-to-next-to-leading order soft function for the production of a massive color octet state at rest in the collision of two massless colored partons in either the fundamental or the adjoint representation. The main application of our result is the determination of the threshold expansion of the heavy-quark pair-production cross sections in the quark annihilation and gluon fusion channels. We discuss the factorization necessary for this purpose and explain the relationship between hard functions and virtual amplitudes

    Matching the Nagy-Soper parton shower at next-to-leading order

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    We present an Mc@Nlo-like matching of next-to-leading order QCD calculations with the Nagy-Soper parton shower. An implementation of the algorithm within the Helac-Dipoles Monte Carlo generator is used to address the uncertainties and ambiguities of the matching scheme. First results obtained using the Nagy-Soper parton shower implementation in Deductor in conjunction with the Helac-Nlo framework are given for the pp → t t ¯ j + X ppttj+X pp\to t\overline{t}j+X process at the LHC with s = 8 s=8 \sqrt{s}=8 TeV. Effects of resummation are discussed for various observables

    Higgs boson to di-tau channel in chargino-neutralino searches at the LHC

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    We consider chargino-neutralino production, χ ˜ 2 0 χ ˜ 1 ± → h χ ˜ 1 0 W ± χ ˜ 1 0 χ~20χ~1±(hχ~10)(W±χ~10) {\tilde{\chi}}_2^0{\tilde{\chi}}_1^{\pm}\to \left(h{\tilde{\chi}}_1^0\right)\left({W}^{\pm }{\tilde{\chi}}_1^0\right) , which results in Higgs boson final states that subsequently decay (inclusively) to leptons (either h → τ + τ − or h → W + W − → ( e + e − ,μ + μ − ,τ + τ − )+ T ). Such channels are dominant in large regions of the allowed supersymmetric parameter space for many concrete supersymmetric models. The existence of leptons allows for good control over the backgrounds, rendering this channel competitive to the conventional h → b b ¯ bb b\overline{b} channel. We include hadronic decays of the τ leptons in our analysis through a τ -identification algorithm. We consider integrated luminosities of 100 fb −1 , 300 fb −1 and 3000 fb −1 , for an LHC running at pp centre-of-mass energy of 14 TeV and provide the expected constraints on the M 2 - M 1 plane

    Comparing EFT and exact one-loop analyses of non-degenerate stops

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    We develop a universal approach to the one-loop effective field theory (EFT) using the Covariant Derivative Expansion (CDE) method. We generalise previous results to include broader classes of UV models, showing how expressions previously obtained assuming degenerate heavy-particle masses can be extended to non-degenerate cases. We apply our method to the general MSSM with non-degenerate stop squarks, illustrating our approach with calculations of the coefficients of dimension-6 operators contributing to the hgg and hγγ couplings, and comparing with exact calculations of one-loop Feynman diagrams. We then use present and projected future sensitivities to these operator coefficients to obtain present and possible future indirect constraints on stop masses. The current sensitivity is already comparable to that of direct LHC searches, and future FCC-ee measurements could be sensitive to stop masses above a TeV. The universality of our one-loop EFT approach facilitates extending these constraints to a broader class of UV models

    Lattice QCD

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    A general introduction to lattice QCD suitable for graduate students in experimental and theoretical particle physics. Aimed at those who want to know how lattice calculations are done, and what the pitfalls are, without having to do the calculations themselves.Comment: Lectures given at 55th Scottish Universities Summer School, St Andrews, August 200

    Physics of Binary Information

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    Basic concepts of theoretical particle physics, including quantum mechanics and Poincar\'e invariance, the leptonic mass spectrum and the proton mass, can be derived, without reference to first principles, from intrinsic properties of the simplest elements of information represented by binary data. What we comprehend as physical reality is, therefore, a reflection of mathematically determined logical structures, built from elements of binary data.Comment: 8 page

    The Charm of Theoretical Physics (1958-1993)

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    Personal recollections on theoretical particle physics in the years when the Standard Theory was formed. In the background, the remarkable development of Italian theoretical physics in the second part of the last century, with great personalities like Bruno Touschek, Raoul Gatto, Nicola Cabibbo and their schools.Comment: 53 pages, 12 figures, to be published in The European Physical Journal H. New version with added text and figure

    The Future of U.S. Particle Theory: Report of the DPF Theory Panel

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    This report summarizes the findings of the DPF Theory Panel which was formed with a goal of understanding the scientific problems and opportunities of the next decade, as well as the challenges involved in sustaining a first-class program in theoretical particle physics research in the United States.Comment: 23 pages, LaTeX, Chapter 5 of the report "Planning the Future of U.S. Particle Physics (Snowmass 2013)

    Computer Algebra in Particle Physics

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    These lectures given to graduate students in theoretical particle physics, provide an introduction to the ``inner workings'' of computer algebra systems. Computer algebra has become an indispensable tool for precision calculations in particle physics. A good knowledge of the basics of computer algebra systems allows one to exploit these systems more efficiently.Comment: 56 pages, lectures given at the "Seminario Nazionale di Fisica Teorica", Parma, September 200
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