Charalampos Anastasiou

ETH Zurich, Zürich, Zurich, Switzerland

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Publications (55)229.3 Total impact

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    ABSTRACT: We compute the NNLO QCD corrections for the hadroproduction of a pair of off-shell photons in the limit of a large number of quark flavors. We perform a reduction of the two-loop amplitude to master integrals and calculate the latter analytically as a Laurent series in the dimensional regulator using modern integration methods. Real radiation corrections are evaluated numerically with a direct subtraction of infrared limits which we cast in a simple factorized form. The results presented here constitute a gauge invariant part of the full NNLO corrections but are not necessarily dominant. We view this calculation as a step towards a complete computation. Our partial corrections to the total cross-section are about $1\%-3\%$ and vary with the virtuality of the two off-shell photons.
    08/2014;
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    ABSTRACT: We present the cross-section for the threshold production of the Higgs boson at hadron-colliders at next-to-next-to-next-to-leading order (N3LO) in perturbative QCD. We present an analytic expression for the partonic cross-section at threshold and the impact of these corrections on the numerical estimates for the hadronic cross-section at the LHC. With this result we achieve a major milestone towards a complete evaluation of the cross-section at N3LO which will reduce the theoretical uncertainty in the determination of the strengths of the Higgs boson interactions.
    Physics Letters B 03/2014; 737. · 4.57 Impact Factor
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    ABSTRACT: We compute the contributions to the N3LO inclusive Higgs boson cross-section from the square of one-loop amplitudes with a Higgs boson and three QCD partons as external states. Our result is a Taylor expansion in the dimensional regulator epsilon, where the coefficients of the expansion are analytic functions of the ratio of the Higgs boson mass and the partonic center of mass energy and they are valid for arbitrary values of this ratio. We also perform a threshold expansion around the limit of soft-parton radiation in the final state. The expressions for the coefficients of the threshold expansion are valid for arbitrary values of the dimension. As a by-product of the threshold expansion calculation, we have developed a soft expansion method at the integrand level by identifying the relevant soft and collinear regions for the loop-momentum.
    Journal of High Energy Physics 11/2013; 2013(12). · 5.62 Impact Factor
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    Charalampos Anastasiou, Claude Duhr, Falko Dulat, Bernhard Mistlberger
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    ABSTRACT: We present the two first terms in the threshold expansion of Higgs production partonic cross-sections at hadron colliders for processes with three partons in the final state. These are contributions to the inclusive Higgs cross-section in gluon fusion at N3LO. We have developed a new technique for the expansion of the squared matrix-elements around the soft limit and for the reduction of the required phase-space integrals to only ten single-scale master integrals. We compute the master integrals building upon modern techniques for the integration of multidimensional integrals in dimensional regularization. Our results constitute an important step towards a systematic computation of the Higgs boson cross-section as an expansion around the threshold limit.
    Journal of High Energy Physics 02/2013; 2013(7). · 5.62 Impact Factor
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    Charalampos Anastasiou, Stephan Buehler, Claude Duhr, Franz Herzog
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    ABSTRACT: We evaluate all phase space master integrals which are required for the total cross section of generic 2 -> 1 processes at NNLO as a series expansion in the dimensional regulator epsilon. Away from the limit of threshold production, our expansion includes one order higher than what has been available in the literature. At threshold, we provide expressions which are valid to all orders in terms of Gamma functions and hypergeometric functions. These results are a necessary ingredient for the renormalization and mass factorization of singularities in 2 -> 1 inclusive cross sections at NNNLO in QCD.
    Journal of High Energy Physics 08/2012; 2012(11). · 5.62 Impact Factor
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    ABSTRACT: We present the inclusive Higgs boson cross-section at the LHC with collision energy of 8 TeV. Our predictions are obtained using our publicly available program iHixs which incorporates NNLO QCD corrections and electroweak corrections. We review the convergence of the QCD perturbative expansion at this new energy and examine the impact of finite Higgs width effects. We also study the impact of different parton distribution functions on the cross-section. We present tables with the cross-section values and estimates for their uncertainty due to uncalculated higher orders in the perturbative expansion and parton densities.
    Journal of High Energy Physics 02/2012; 2012(4). · 5.62 Impact Factor
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    Charalampos Anastasiou, Franz Herzog, Achilleas Lazopoulos
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    ABSTRACT: The decay of a light Higgs boson to bottom quarks is dominant and can be exploited for the discovery of the Higgs particle and the measurement of its properties at the LHC and future collider experiments. We perform a first computation of the fully differential decay at next-next-to-leading order in perturbative QCD. We employ a novel method of non-linear mappings for the treatment of singularities in the radiative processes which contribute to the decay width. This constitutes the first physical application of the method.
    Journal of High Energy Physics 10/2011; · 5.62 Impact Factor
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    ABSTRACT: We present a new program (iHixs) which computes the inclusive Higgs boson cross-section at hadron colliders. It incorporates QCD corrections through NNLO, real and virtual electroweak corrections, mixed QCD-electroweak corrections, quark-mass effects through NLO in QCD, and finite width effects for the Higgs boson and heavy quarks. iHixs can be used to obtain the most precise cross-section values in fixed order perturbation theory in the Standard Model. In addition, it allows for a consistent evaluation of the cross-section in modified Higgs boson sectors with anomalous Yukawa and electroweak interactions as required in extensions of the Standard Model. iHixs is interfaced with the LHAPDF library and can be used with all available NNLO sets of parton distribution functions.
    Journal of High Energy Physics 07/2011; · 5.62 Impact Factor
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    ABSTRACT: We present theoretical predictions for the Higgs boson production cross-section via gluon fusion at the LHC in a Standard Model with four generations. We include QCD corrections through NLO retaining the full dependence on the quark masses, and the NNLO corrections in the heavy quark effective theory approximation. We also include electroweak corrections through three loops. Electroweak and bottom-quark contributions are suppressed in comparison to the Standard Model with three generations.
    Physics Letters B 03/2011; 702(4). · 4.57 Impact Factor
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    Charalampos Anastasiou, Andrea Banfi
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    ABSTRACT: {N} = 4 supersymmetric Yang-Mills theory exhibits a rather surprising duality of Wilson-loop vacuum expectation values and scattering amplitudes. In this paper, we investigate this correspondence at the diagram level. We find that one-loop triangles, one-loop boxes, and two-loop diagonal boxes can be cast as simple one-and two-parametric integrals over a single propagator in configuration space. We observe that the two-loop Wilson-loop "hard-diagram" corresponds to a four-loop hexagon Feynman diagram. Guided by the diagrammatic correspondence of the configuration-space propagator and loop Feynman diagrams, we derive Feynman parameterizations of complicated planar and non-planar Feynman diagrams which simplify their evaluation. For illustration, we compute numerically a four-loop hexagon scalar Feynman diagram.
    Journal of High Energy Physics 02/2011; 2. · 5.62 Impact Factor
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    Charalampos Anastasiou, Andrea Banfi
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    ABSTRACT: supersymmetric Yang-Mills theory exhibits a rather surprising duality of Wilson-loop vacuum expectation values and scattering amplitudes. In this paper, we investigate this correspondence at the diagram level. We find that one-loop triangles, one-loop boxes, and two-loop diagonal boxes can be cast as simple one-and two-parametric integrals over a single propagator in configuration space. We observe that the two-loop Wilson-loop “hard-diagram” corresponds to a four-loop hexagon Feynman diagram. Guided by the diagrammatic correspondence of the configuration-space propagator and loop Feynman diagrams, we derive Feynman parameterizations of complicated planar and non-planar Feynman diagrams which simplify their evaluation. For illustration, we compute numerically a four-loop hexagon scalar Feynman diagram.
    Journal of High Energy Physics - J HIGH ENERGY PHYS. 01/2011; 2011(2):1-21.
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    Charalampos Anastasiou, Franz Herzog, Achilleas Lazopoulos
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    ABSTRACT: Real and virtual corrections in NNLO QCD require multi-dimensional integrals with overlapping singularities. We first review ideas and methods which have been proposed for performing such computations. We then present a new method for the factorization of overlapping singularities based on non-linear integral transformations. We apply this method for the evaluation of all integral topologies which appear in double real radiation corrections in cross-section calculations for the production of a heavy system at hadron colliders. Finally, we demonstrate with typical examples that two-loop virtual corrections are amenable to the same method.
    Journal of High Energy Physics 11/2010; 2011(3). · 5.62 Impact Factor
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    ABSTRACT: We compute for the first time the two-loop corrections to arbitrary n-gon lightlike Wilson loops in N = 4 supersymmetric Yang-Mills theory, using efficient numerical methods. The calculation is motivated by the remarkable agreement between the finite part of planar six-point MHV amplitudes and hexagon Wilson loops which has been observed at two loops. At n = 6 we confirm that the ABDK/BDS ansatz must be corrected by adding a remainder function, which depends only on conformally invariant ratios of kinematic variables. We numerically compute remainder functions for n = 7, 8 and verify dual conformal invariance. Furthermore, we study simple and multiple collinear limits of the Wilson loop remainder functions and demonstrate that they have precisely the form required by the collinear factorisation of the cor-responding two-loop n-point amplitudes. The number of distinct diagram topologies contributing to the n-gon Wilson loops does not increase with n, and there is a fixed number of "master integrals", which we have computed. Thus we have essentially computed general polygon Wilson loops, and if the correspondence with amplitudes continues to hold, all planar n-point two-loop MHV amplitudes in the N = 4 theory.
    Journal of High Energy Physics 07/2010; 2009(05). · 5.62 Impact Factor
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    Charalampos Anastasiou, Radja Boughezal, Elisabetta Furlan
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    ABSTRACT: We consider extensions of the Standard Model with a number of additional heavy quarks which couple to the Higgs boson via top-like Yukawa interactions. We construct an effective theory valid for a Higgs boson mass which is lighter than twice the lightest heavy quark mass and compute the corresponding Wilson coefficient through NNLO. We present numerical results for the gluon fusion cross-section at the Tevatron for an extension of the Standard Model with a fourth generation of heavy quarks. The gluon fusion cross-section at NLO and in the approximation of infinitely heavy quarks is enhanced by a factor of 9 with respect to the Standard Model value. Tevatron experimental data can place stringent exclusion limits for the Higgs mass in this model. We find that the relative magnitude of the higher order QCD corrections with respect to the LO is similar to the Standard Model. Our result serves to carry out an exclusion analysis for a four-generation Standard Model with the same accuracy as in the Standard Model analysis. KeywordsHiggs Physics-NLO Computations
    Journal of High Energy Physics 03/2010; 2010(6):1-15. · 5.62 Impact Factor
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    ABSTRACT: The Tevatron experiments have recently excluded a Standard Model Higgs boson in the mass range 160 GeV < mH < 170 GeV at the 95% confidence level. This result is based on sophisticated analyses designed to maximize the ratio of accepted signal to background. In this paper we study the production of a Higgs boson of mass mH = 160 GeV in the gg → H → WW → lνlν channel. We choose a set of cuts like those adopted in the experimental analysis and compare kinematical distributions of the final state leptons computed in NNLO QCD to lower-order calculations and to those obtained with the event generators PYTHIA, HERWIG and MC@NLO. We also show that the distribution of the output from an Artificial Neural Network obtained with the different tools does not show significant differences. However, the final acceptance computed with PYTHIA is smaller than those obtained at NNLO and with HERWIG and MC@NLO. We also investigate the impact of the underlying event and hadronization on our results.
    Journal of High Energy Physics 08/2009; 2009(08):099. · 5.62 Impact Factor
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    Charalampos Anastasiou, Stefan Bucherer, Zoltan Kunszt
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    ABSTRACT: We compute fully differential next-to-leading order QCD cross-sections for Higgs boson production via gluon fusion in the Standard Model. We maintain the full dependence of the cross-sections on the top and bottom quark mass. We find that finite quark mass effects are important given the achieved precision of QCD predictions for gluon fusion. Our Monte-Carlo program, HPro, can correct existing NNLO fully differential calculations, which employ the approximation of an infinitely heavy top and a vanishing bottom quark Yukawa coupling, for heavy quark finite mass effects through NLO. Comment: References added. Discussion of small-x effects on the Higgs rapidity distribution added
    Journal of High Energy Physics 07/2009; · 5.62 Impact Factor
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    Charalampos Anastasiou, Elisabetta Furlan, Jose Santiago
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    ABSTRACT: We study the role of fermionic resonances in realistic composite Higgs models. We consider the low energy effective description of a model in which the Higgs arises as the pseudo-Goldstone boson of an SO(5)/SO(4) global symmetry breaking pattern. Assuming that only fermionic resonances are present below the cut-off of our effective theory, we perform a detailed analysis of the electroweak constraints on such a model. This includes the exact one-loop calculation of the T parameter and the anomalous Zbb coupling for arbitrary new fermions and couplings. Other relevant observables, like b to s gamma and Delta B=2 processes have also been examined. We find that, while minimal models are difficult to make compatible with electroweak precision tests, models with several fermionic resonances, such as the ones that appear in the spectrum of viable composite Higgs models from warped extra dimensions, are fully realistic in a large region of parameter space. These fermionic resonances could be the first observable signature of the model at the LHC. Comment: 33 pages, 8 figures
    Physical review D: Particles and fields 01/2009;
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    Charalampos Anastasiou, S. Mert Aybat
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    ABSTRACT: We compute the one-loop QCD amplitude for the process gg→QQ̅ in dimensional regularization through order ϵ2 in the dimensional regulator and for arbitrary quark mass values. This result is an ingredient of the next-to-next-to-leading order cross section for heavy-quark production at hadron colliders. The calculation is performed in conventional dimensional regularization using well-known reduction techniques as well as a method based on recent ideas for the functional form of one-loop integrands in four dimensions.
    Physical review D: Particles and fields 12/2008; 78(11).
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    Charalampos Anastasiou, Radja Boughezal, Frank Petriello
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    ABSTRACT: We compute the 3-loop O(\alpha \alpha_s) correction to the Higgs boson production cross section arising from light quarks using an effective theory approach. Our calculation probes the factorization of QCD and electroweak perturbative corrections to this process. We combine our results with the best current estimates for contributions from top and bottom quarks to derive an updated theoretical prediction for the Higgs boson production cross section in gluon fusion. With the use of the MSTW 2008 parton distribution functions that include the newest experimental data, our study results in cross sections approximately 4-6% lower for intermediate Higgs boson masses than those used in recent Tevatron analyses that imposed a 95% confidence level exclusion limit of a Standard Model Higgs boson with M_H=170 GeV. Comment: 16 pgs., 5 figs. References and discussion added. Numerical results updated to use recent MSTW 2008 PDFs, which decrease the predicted Tevatron cross section
    Journal of High Energy Physics 11/2008; · 5.62 Impact Factor
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    Charalampos Anastasiou, Stefan Beerli, Alejandro Daleo
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    ABSTRACT: We present the two-loop QCD amplitude for the interaction of two gluons and a CP-even Higgs boson in the minimal supersymmetric standard model (MSSM). We apply a novel numerical method for the evaluation of Feynman diagrams with infrared, ultraviolet, and threshold singularities. We discuss subtleties in the ultraviolet renormalization of the amplitude with conventional dimensional regularization, dimensional reduction, and the four dimensional helicity scheme. Finally, we show numerical results for scenarios of supersymmetry breaking with a rather challenging phenomenology in which the Higgs signal in the MSSM is suppressed in comparison to the standard model.
    Physical Review Letters 06/2008; 100(24):241806. · 7.73 Impact Factor

Publication Stats

3k Citations
229.30 Total Impact Points

Institutions

  • 2005–2013
    • ETH Zurich
      • Institute for Theoretical Physics
      Zürich, Zurich, Switzerland
    • Johns Hopkins University
      • Department of Physics and Astronomy
      Baltimore, MD, United States
  • 1999–2010
    • Durham University
      • Department of Physics
      Durham, England, United Kingdom
  • 2007
    • CERN
      Genève, Geneva, Switzerland
  • 2002–2004
    • Stanford University
      • Stanford Linear Accelerator Center
      Stanford, CA, United States