Charalampos Anastasiou

ETH Zurich, Zürich, Zurich, Switzerland

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Publications (60)292.15 Total impact

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    ABSTRACT: We present methods to compute higher orders in the threshold expansion for the one-loop production of a Higgs boson in association with two partons at hadron colliders. This process contributes to the N$^3$LO Higgs production cross section beyond the soft-virtual approximation. We use reverse unitarity to expand the phase-space integrals in the small kinematic parameters and to reduce the coefficients of the expansion to a small set of master integrals. We describe two methods for the calculation of the master integrals. The first was introduced for the calculation of the soft triple-real radiation relevant to N$^3$LO Higgs production. The second uses a particular factorization of the three body phase-space measure and the knowledge of the scaling properties of the integral itself. Our result is presented as a Laurent expansion in the dimensional regulator, although some of the master integrals are computed to all orders in this parameter.
    Preview · Article · May 2015 · Journal of High Energy Physics
  • Charalampos Anastasiou · Claude Duhr · Falko Dulat · Franz Herzog · Bernhard Mistlberger
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    ABSTRACT: We present the cross section for the production of a Higgs boson at hadron colliders at next-to-next-to-next-to-leading order (N^{3}LO) in perturbative QCD. The calculation is based on a method to perform a series expansion of the partonic cross section around the threshold limit to an arbitrary order. We perform this expansion to sufficiently high order to obtain the value of the hadronic cross at N^{3}LO in the large top-mass limit. For renormalization and factorization scales equal to half the Higgs boson mass, the N^{3}LO corrections are of the order of +2.2%. The total scale variation at N^{3}LO is 3%, reducing the uncertainty due to missing higher order QCD corrections by a factor of 3.
    No preview · Article · May 2015 · Physical Review Letters
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    ABSTRACT: In this article, we compute the gluon fusion Higgs boson cross-section at N3LO through the second term in the threshold expansion. This calculation constitutes a major milestone towards the full N3LO cross section. Our result has the best formal accuracy in the threshold expansion currently available, and includes contributions from collinear regions besides subleading corrections from soft and hard regions, as well as certain logarithmically enhanced contributions for general kinematics. We use our results to perform a critical appraisal of the validity of the threshold approximation at N3LO in perturbative QCD.
    Preview · Article · Mar 2015 · Journal of High Energy Physics
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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.
    Preview · Article · Feb 2015 · Journal of High Energy Physics
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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.
    Preview · Article · Aug 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.
    Full-text · Article · Mar 2014 · Physics Letters B
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    Charalampos Anastasiou · Claude Duhr · Falko Dulat · Franz Herzog · Bernhard Mistlberger
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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.
    Full-text · Article · Nov 2013 · Journal of High Energy Physics
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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.
    Preview · Article · Feb 2013 · Journal of High Energy Physics
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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.
    Preview · Article · Aug 2012 · Journal of High Energy Physics
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    Charalampos Anastasiou · Stephan Buehler · Franz Herzog · Achilleas Lazopoulos
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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.
    Full-text · Article · Feb 2012 · Journal of High Energy Physics
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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.
    Full-text · Article · Oct 2011 · Journal of High Energy Physics
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    Charalampos Anastasiou · Stephan Buehler · Franz Herzog · Achilleas Lazopoulos
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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.
    Full-text · Article · Jul 2011 · Journal of High Energy Physics
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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.
    Full-text · Article · Mar 2011 · Physics Letters B
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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.
    Preview · Article · Feb 2011 · Journal of High Energy Physics
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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.
    Full-text · Article · Nov 2010 · Journal of High Energy Physics
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    C Anastasiou · A Brandhuber · P Heslop · V.V Khoze · B Spence · G Travaglini
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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.
    Full-text · Article · Jul 2010 · Journal of High Energy Physics
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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
    Full-text · Article · Mar 2010 · Journal of High Energy Physics
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    Charalampos Anastasiou · Gunther Dissertori · Fabian Stockli · Bryan R Webber
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    ABSTRACT: The discovery of a Standard Model Higgs boson is possible when experimental cuts are applied which increase the ratio of signal and background cross-sections. In this paper we study the pp → H → WW signal cross-section at the LHC which requires a selection of Higgs bosons with small transverse momentum. We compare predictions for the efficiency of the experimental cuts from a NNLO QCD calculation, a calculation of the resummation of logarithms in the transverse momentum of the Higgs boson at NNLL, and the event generator MC@NLO. We also investigate the impact of various jet-algorithms, the underlying event and hadronization on the signal cross-section.
    Preview · Article · Jan 2010
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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.
    Preview · Article · Aug 2009 · Journal of High Energy Physics
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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
    Full-text · Article · Jul 2009 · Journal of High Energy Physics

Publication Stats

5k Citations
292.15 Total Impact Points

Institutions

  • 2005-2015
    • ETH Zurich
      • Institute for Theoretical Physics
      Zürich, Zurich, Switzerland
  • 2007
    • CERN
      Genève, Geneva, Switzerland
  • 2004
    • Johns Hopkins University
      Baltimore, Maryland, United States
  • 2002-2004
    • Stanford University
      • SLAC National Accelerator Laboratory
      Palo Alto, California, United States
  • 1999-2002
    • Durham University
      • Department of Physics
      Durham, England, United Kingdom