290 research outputs found
Two-Loop Corrections to Top-Antitop Production at Hadron Colliders
The status of the theoretical predictions for the top-anti top production in
hadronic collisions is shortly reviewed, paying a articular attention to the
analytic calculation of the two-loop QCD corrections to the parton-level matrix
elements.Comment: Talk presented at the 35th International Conference of High Energy
Physics - ICHEP2010, July 22-28, 2010, Paris Franc
Two-loop corrections to top-antitop production at hadron colliders
The status of the theoretical predictions for the top-anti top production in hadronic collisions is shortly reviewed, paying a articular attention to the analytic calculation of the two-loop QCD corrections to the parton-level matrix elements
Adaptive multigrid algorithm for the lattice Wilson-Dirac operator
We present an adaptive multigrid solver for application to the non-Hermitian
Wilson-Dirac system of QCD. The key components leading to the success of our
proposed algorithm are the use of an adaptive projection onto coarse grids that
preserves the near null space of the system matrix together with a simplified
form of the correction based on the so-called gamma_5-Hermitian symmetry of the
Dirac operator. We demonstrate that the algorithm nearly eliminates critical
slowing down in the chiral limit and that it has weak dependence on the lattice
volume
The Sixth Copper Mountain Conference on Multigrid Methods, part 1
The Sixth Copper Mountain Conference on Multigrid Methods was held on 4-9 Apr. 1993, at Copper Mountain, CO. This book is a collection of many of the papers presented at the conference and as such represents the conference proceedings. NASA LaRC graciously provided printing of this document so that all of the papers could be presented in a single forum. Each paper was reviewed by a member of the conference organizing committee under the coordination of the editors. The multigrid discipline continues to expand and mature, as is evident from these proceedings. The vibrancy in this field is amply expressed in these important papers, and the collection clearly shows its rapid trend to further diversity and depth
production at hadron colliders in NNLO QCD
Charged gauge boson pair production at the Large Hadron Collider allows
detailed probes of the fundamental structure of electroweak interactions. We
present precise theoretical predictions for on-shell production that
include, for the first time, QCD effects up to next-to-next-to-leading order in
perturbation theory. As compared to next-to-leading order, the inclusive
cross section is enhanced by 9% at 7 TeV and 12% at 14 TeV. The
residual perturbative uncertainty is at the 3% level. The severe contamination
of the cross section due to top-quark resonances is discussed in
detail. Comparing different definitions of top-free production in the
four and five flavour number schemes, we demonstrate that top-quark resonances
can be separated from the inclusive cross section without significant
loss of theoretical precision.Comment: 7 pages, 3 figure
Loopedia, a Database for Loop Integrals
Loopedia is a new database at loopedia.org for information on Feynman
integrals, intended to provide both bibliographic information as well as
results made available by the community. Its bibliometry is complementary to
that of SPIRES or arXiv in the sense that it admits searching for integrals by
graph-theoretical objects, e.g. its topology.Comment: 16 pages, lots of screenshot
Multilevel first-order system least squares for nonlinear elliptic partial differential equations
A fully variational approach is developed for solving nonlinear elliptic equations that enables accurate discretization and fast solution methods. The equations are converted to a first-order system that is then linearized via Newton's method. First-order system least squares (FOSLS) is used to formulate and discretize the Newton step, and the resulting matrix equation is solved using algebraic multigrid (AMG). The approach is coupled with nested iteration to provide an accurate initial guess for finer levels using coarse-level computation. A general theory is developed that confirms the usual full multigrid efficiency: accuracy comparable to the finest-level discretization is achieved at a cost proportional to the number of finest-level degrees of freedom. In a companion paper, the theory is applied to elliptic grid generation (EGG) and supported by numerical results
Determining the global minimum of Higgs potentials via Groebner bases - applied to the NMSSM
Determining the global minimum of Higgs potentials with several Higgs fields
like the next-to-minimal supersymmetric extension of the Standard Model (NMSSM)
is a non-trivial task already at the tree level. The global minimum of a Higgs
potential can be found from the set of all its stationary points defined by a
multivariate polynomial system of equations. We introduce here the algebraic
Groebner basis approach to solve this system of equations. We apply the method
to the NMSSM with CP conserving as well as CP violating parameters. The results
reveal an interesting stationary-point structure of the potential. Requiring
the global minimum to give the electroweak symmetry breaking observed in Nature
excludes large parts of the parameter space.Comment: 10 pages, 2 figure
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