5,587 research outputs found
Weak boson fusion production of supersymmetric particles at the LHC
We present a complete calculation of weak boson fusion production of
colorless supersymmetric particles at the LHC, using the new matrix element
generator SUSY-MadGraph. The cross sections are small, generally at the
attobarn level, with a few notable exceptions which might provide additional
supersymmetric parameter measurements. We discuss in detail how to consistently
define supersymmetric weak couplings to preserve unitarity of weak gauge boson
scattering amplitudes to fermions, and derive sum rules for weak supersymmetric
couplings.Comment: 24 p., 3 fig., 9 tab., published in PRD; numbers in Table IV
corrected to those with kinematic cuts cite
Calculation of HELAS amplitudes for QCD processes using graphics processing unit (GPU)
We use a graphics processing unit (GPU) for fast calculations of helicity
amplitudes of quark and gluon scattering processes in massless QCD. New HEGET
({\bf H}ELAS {\bf E}valuation with {\bf G}PU {\bf E}nhanced {\bf T}echnology)
codes for gluon self-interactions are introduced, and a C++ program to convert
the MadGraph generated FORTRAN codes into HEGET codes in CUDA (a C-platform for
general purpose computing on GPU) is created. Because of the proliferation of
the number of Feynman diagrams and the number of independent color amplitudes,
the maximum number of final state jets we can evaluate on a GPU is limited to 4
for pure gluon processes (), or 5 for processes with one or more
quark lines such as and . Compared with the usual
CPU-based programs, we obtain 60-100 times better performance on the GPU,
except for 5-jet production processes and the processes for which
the GPU gain over the CPU is about 20
Tentative Theses on Transformative Research in Real-World Laboratories: First Insights from the Accompanying Research ForReal
Real-world laboratories are growing in popularity promising a contribution to both: the understanding and facilitation of societal transformation towards sustainability. Baden-Württemberg substantially funds real-world labs as part of the initiative "science for sustainability". To facilitate learning with and from these so-called BaWü-Labs, they are supported by accompanying research conducted by two teams. This article presents first insights and theses on real-world labs as a research format, based in particular on the work of the accompanying research team ForReal. The team supports the labs in their realization and in providing general insights, e.g. by learning from related international research approaches and dialog with international experts, and analyzes suitable quality features and methods (the latter together with the University of Basel team). The theses presented here put up for discussion first insights on real-world labs as a transformative research approach and reflect on them from a theoretical perspective. They illustrate the relevance of a goal-oriented use of methods and present learning processes as core characteristics of real-world labs. The theses were formulated based on discussions with the BaWü-Labs, exchange in international contexts as well as a thematic literature review
Precise determination of the Wtb couplings at LHC
Top pair production at LHC is the ideal place to search for nonstandard Wtb
couplings in t -> W b -> l nu b decays. The lb forward-backward asymmetry in
the W rest frame is very sensitive to sigma_{mu nu} couplings, and can spot
one-loop QCD corrections to the decay vertex with more than 5 sigma statistical
significance. We discuss the potential of this asymmetry to signal nonstandard
gamma_mu and sigma_{mu nu} couplings and compare with top-antitop spin
correlation asymmetries, which have a lower sensitivity. We also briefly
summarise the results for Tevatron.Comment: LaTeX, 12 pages, 2 PS figures. One reference added. To be published
in PR
Tracking the Orbital and Super-orbital Periods of SMC X-1
The High Mass X-ray Binary (HMXB) SMC X-1 demonstrates an orbital variation
of 3.89 days and a super-orbital variation with an average length of 55 days.
As we show here, however, the length of the super-orbital cycle varies by
almost a factor of two, even across adjacent cycles. To study both the orbital
and super-orbital variation we utilize lightcurves from the Rossi X-ray Timing
Explorer All Sky Monitor (RXTE-ASM). We employ the orbital ephemeris from
Wojdowski et al. (1998) to obtain the average orbital profile, and we show that
this profile exhibits complex modulation during non-eclipse phases.
Additionally, a very interesting ``bounceback'' in X-ray count rate is seen
during mid-orbital eclipse phases, with a softening of the emission during
these periods. This bounceback has not been previously identified in pointed
observations. We then define a super-orbital ephemeris (the phase of the
super-orbital cycle as a function of date) based on the ASM lightcurve and
analyze the trend and distribution of super-orbital cycle lengths. SMC X-1
exhibits a bimodal distribution of these lengths, similar to what has been
observed in other systems (e.g., Her X-1), but with more dramatic changes in
cycle length. There is some hint, but not conclusive evidence, for a dependence
of the super-orbital cycle length upon the underlying orbital period, as has
been observed previously for Her X-1 and Cyg X-2. Using our super-orbital
ephemeris we are also able to create an average super-orbital profile over the
71 observed cycles, for which we witness overall hardening of the spectrum
during low count rate times. We combine the orbital and super-orbital
ephemerides to study the correlation between the orbital and super-orbital
variations in the system.Comment: 10 pages, using emulateapj style. To be published in the
Astrophysical Journa
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