30 research outputs found
Two-loop amplitudes and master integrals for the production of a Higgs boson via a massive quark and a scalar-quark loop
We compute all two-loop master integrals which are required for the
evaluation of next-to-leading order QCD corrections in Higgs boson production
via gluon fusion. Many two-loop amplitudes for 2 -> 1 processes in the Standard
Model and beyond can be expressed in terms of these integrals using automated
reduction techniques. These integrals also form a subset of the master
integrals for more complicated 2 -> 2 amplitudes with massive propagators in
the loops. As a first application, we evaluate the two-loop amplitude for Higgs
boson production in gluon fusion via a massive quark. Our result is the first
independent check of the calculation of Spira, Djouadi, Graudenz and Zerwas. We
also present for the first time the two-loop amplitude for gg -> h via a
massive squark
NNLO Antenna Subtraction with One Hadronic Initial State
In this talk we present the extension of the antenna subtraction method to
include initial states containing one hadron at NNLO. We sketch the
requirements for the different necessary subtraction terms, and we explain how
the antenna functions are integrated over the appropriate phase space by
reducing the integrals to a small set of master integrals. Where applicable,
our results for the integrated antennae were cross-checked against the known
NNLO coefficient functions for deep inelastic scattering processes.Comment: 6 pages, 1 figure. Talk given at RADCOR 2009 - 9th International
Symposium on Radiative Corrections (Applications of Quantum Field Theory to
Phenomenology) October 25 - 30 200
The two-loop QCD amplitude gg -> h,H in the Minimal Supersymmetric Standard Model
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. 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.Comment: 5 pages, 3 figure
On the dbar/ubar Asymmetry and Parton Distributions
We discuss the impact of different measurements of the dbar/ubar asymmetry in
the extraction of parameterizations of parton distribution functions.Comment: Contributed paper to LP01, 13 pages, 4 figure
Evaluating multi-loop Feynman diagrams with infrared and threshold singularities numerically
We present a method to evaluate numerically Feynman diagrams directly from
their Feynman parameters representation. We first disentangle overlapping
singularities using sector decomposition. Threshold singularities are treated
with an appropriate contour deformation. We have validated our technique
comparing with recent analytic results for the gg->h two-loop amplitudes with
heavy quarks and scalar quarks.Comment: 8 pages, 3 figures; references added, version to appear in JHE
Z-prime Gauge Bosons at the Tevatron
We study the discovery potential of the Tevatron for a Z-prime gauge boson.
We introduce a parametrization of the Z-prime signal which provides a
convenient bridge between collider searches and specific Z-prime models. The
cross section for p pbar -> Z-prime X -> l^+ l^- X depends primarily on the
Z-prime mass and the Z-prime decay branching fraction into leptons times the
average square coupling to up and down quarks. If the quark and lepton masses
are generated as in the standard model, then the Z-prime bosons accessible at
the Tevatron must couple to fermions proportionally to a linear combination of
baryon and lepton numbers in order to avoid the limits on Z--Z-prime mixing.
More generally, we present several families of U(1) extensions of the standard
model that include as special cases many of the Z-prime models discussed in the
literature. Typically, the CDF and D0 experiments are expected to probe
Z-prime-fermion couplings down to 0.1 for Z-prime masses in the 500--800 GeV
range, which in various models would substantially improve the limits set by
the LEP experiments.Comment: 34 pages, 13 figure
Antenna subtraction with hadronic initial states
The antenna subtraction method for the computation of higher order
corrections to jet observables and exclusive cross sections at collider
experiments is extended to include hadronic initial states. In addition to the
already known antenna subtraction with both radiators in the final state
(final-final antennae), we introduce antenna subtractions with one or two
radiators in the initial state (initial-final or initial-initial antennae). For
those, we derive the phase space factorization and discuss the allowed phase
space mappings at NLO and NNLO. We present integrated forms for all antenna
functions relevant to NLO calculations, and describe the construction of the
full antenna subtraction terms at NLO on two examples. The extension of the
formalism to NNLO is outlined.Comment: 33 pages, 3 figure
Numerical evaluation of loop integrals
We present a new method for the numerical evaluation of arbitrary loop
integrals in dimensional regularization. We first derive Mellin-Barnes integral
representations and apply an algorithmic technique, based on the Cauchy
theorem, to extract the divergent parts in the epsilon->0 limit. We then
perform an epsilon-expansion and evaluate the integral coefficients of the
expansion numerically. The method yields stable results in physical kinematic
regions avoiding intricate analytic continuations. It can also be applied to
evaluate both scalar and tensor integrals without employing reduction methods.
We demonstrate our method with specific examples of infrared divergent
integrals with many kinematic scales, such as two-loop and three-loop box
integrals and tensor integrals of rank six for the one-loop hexagon topology