[Show abstract][Hide abstract] 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.
Journal of High Energy Physics 05/2015; 2015(8). DOI:10.1007/JHEP08(2015)051 · 6.11 Impact Factor
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
Journal of High Energy Physics 03/2015; 2015(3). DOI:10.1007/JHEP03(2015)091 · 6.11 Impact Factor
[Show abstract][Hide abstract] 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.
Journal of High Energy Physics 02/2015; 2015(2). DOI:10.1007/JHEP02(2015)182 · 6.11 Impact Factor
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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. DOI:10.1016/j.physletb.2014.08.067 · 6.13 Impact Factor
[Show abstract][Hide abstract] 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). DOI:10.1007/JHEP12(2013)088 · 6.11 Impact Factor
[Show abstract][Hide abstract] 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). DOI:10.1007/JHEP07(2013)003 · 6.11 Impact Factor
[Show abstract][Hide abstract] 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). DOI:10.1007/JHEP11(2012)062 · 6.11 Impact Factor
[Show abstract][Hide abstract] 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). DOI:10.1007/JHEP04(2012)004 · 6.11 Impact Factor
[Show abstract][Hide abstract] 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; 2012(3). DOI:10.1007/JHEP03(2012)035 · 6.11 Impact Factor
[Show abstract][Hide abstract] 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; 2011(12). DOI:10.1007/JHEP12(2011)058 · 6.11 Impact Factor
[Show abstract][Hide abstract] 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). DOI:10.1016/j.physletb.2011.06.097 · 6.13 Impact Factor
[Show abstract][Hide abstract] 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(2). DOI:10.1007/JHEP02(2011)064 · 6.11 Impact Factor
[Show abstract][Hide abstract] 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). DOI:10.1007/JHEP03(2011)038 · 6.11 Impact Factor
[Show abstract][Hide abstract] 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). DOI:10.1088/1126-6708/2009/05/115 · 6.11 Impact Factor
[Show abstract][Hide abstract] 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. DOI:10.1007/JHEP06(2010)101 · 6.11 Impact Factor
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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. DOI:10.1088/1126-6708/2009/08/099 · 6.11 Impact Factor
[Show abstract][Hide abstract] 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; 2009(10). DOI:10.1088/1126-6708/2009/10/068 · 6.11 Impact Factor