36 research outputs found
A model of a transition neutral pion formfactor measured in annihilation and scattering channels
We consider an alternative explanation of newly found growth of neutral pion
transition form factor with virtuality of one of photon. It is based on Sudakov
suppression of quark-photon vertex. Some applications to scattering and
annihilation channels are considered including the relevant experiments with
lepton-proton scattering.Comment: 5 pages, 4 figur
Resummation of Yukawa enhanced and subleading Sudakov logarithms in longitudinal gauge boson and Higgs production
Future colliders will probe the electroweak theory at energies much larger
than the gauge boson masses. Large double (DL) and single (SL) logarithmic
virtual electroweak Sudakov corrections lead to significant effects for
observable cross sections. Recently, leading and subleading universal
corrections for external fermions and transverse gauge boson lines were
resummed by employing the infrared evolution equation method. The results were
confirmed at the DL level by explicit two loop calculations with the physical
Standard Model (SM) fields. Also for longitudinal degrees of freedom the
approach was utilized for DL-corrections via the Goldstone boson equivalence
theorem. In all cases, the electroweak Sudakov logarithms exponentiate. In this
paper we extend the same approach to both Yukawa enhanced as well as subleading
Sudakov corrections to longitudinal gauge boson and Higgs production. We use
virtual contributions to splitting functions of the appropriate Goldstone
bosons in the high energy regime and find that all universal subleading terms
exponentiate. The approach is verified by employing a non-Abelian version of
Gribov's factorization theorem and by explicit comparison with existing one
loop calculations. As a side result, we obtain also all top-Yukawa enhanced
subleading logarithms for chiral fermion production at high energies to all
orders. In all cases, the size of the subleading contributions at the two loop
level is non-negligible in the context of precision measurements at future
linear colliders.Comment: 32 pages, 7 figures, uses LaTeX2
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Massively-parallel electrical-conductivity imaging of hydrocarbonsusing the Blue Gene/L supercomputer
Large-scale controlled source electromagnetic (CSEM)three-dimensional (3D) geophysical imaging is now receiving considerableattention for electrical conductivity mapping of potential offshore oiland gas reservoirs. To cope with the typically large computationalrequirements of the 3D CSEM imaging problem, our strategies exploitcomputational parallelism and optimized finite-difference meshing. Wereport on an imaging experiment, utilizing 32,768 tasks/processors on theIBM Watson Research Blue Gene/L (BG/L) supercomputer. Over a 24-hourperiod, we were able to image a large scale marine CSEM field data setthat previously required over four months of computing time ondistributed clusters utilizing 1024 tasks on an Infiniband fabric. Thetotal initial data misfit could be decreased by 67 percent within 72completed inversion iterations, indicating an electrically resistiveregion in the southern survey area below a depth of 1500 m below theseafloor. The major part of the residual misfit stems from transmitterparallel receiver components that have an offset from the transmittersail line (broadside configuration). Modeling confirms that improvedbroadside data fits can be achieved by considering anisotropic electricalconductivities. While delivering a satisfactory gross scale image for thedepths of interest, the experiment provides important evidence for thenecessity of discriminating between horizontal and verticalconductivities for maximally consistent 3D CSEM inversions
Resummation of double logarithms in electroweak high energy processes
At future linear collider experiments in the TeV range, Sudakov
double logarithms originating from massive boson exchange can lead to
significant corrections to the cross sections of the observable processes.
These effects are important for the high precision objectives of the Next
Linear Collider. We use the infrared evolution equation, based on a gauge
invariant dispersive method, to obtain double logarithmic asymptotics of
scattering amplitudes and discuss how it can be applied, in the case of broken
gauge symmetry, to the Standard Model of electroweak processes. We discuss the
double logarithmic effects to both non-radiative processes and to processes
accompanied by soft gauge boson emission. In all cases the Sudakov double
logarithms are found to exponentiate. We also discuss double logarithmic
effects of a non-Sudakov type which appear in Regge-like processes.Comment: 26 pages, 3 figures, Latex2
On the Resummation of Large QCD Logarithms in Higgs -> 2 Photons Decay
We study the strong corrections to the Higgs coupling to two photons. This
coupling is the dominant mechanism for Higgs production in photon-photon
collisions. In addition, the two photon decay mode of the Higgs is an important
and relatively background free channel of relevance at the LHC and the
Tevatron. We develop a method for the resummation of large QCD corrections in
the form of Sudakov-like logarithms of the type \alpha_s^n\ln^{2n}(m/m_H) and
\alpha_s^n\ln^{2n-1}(m/m_H) (where m is the light quark mass) which can
contribute to this process in certain models (for example, the MSSM for large
tan \beta) up to next-to-leading-logarithmic (NLL) accuracy. The NLL correction
is moderate, the substantial part of which comes from terms not related to
running coupling effects.Comment: 13 pages, LaTeX, 5 Postscript Figures, version published in Phys.
Rev.
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Mitigating Distortion During Sintering of Binder Jet Printed Ceramics
Sintering increases the strength of binder jet 3D printed green bodies through densification,
but with the potential cost of distortion due to creep. In this work, we determine how a reactive
binder affects such distortion during sintering of titanium dioxide green bodies. The binder
decomposes to form nanocrystalline interparticle necks during the early stages of the sintering
process. We first characterize the decomposition of the reactive binder through thermogravimetry,
differential scanning calorimetry, and x-ray diffraction. Next, we elucidate the effect of this
precursor on the shrinkage of cylindrical parts using dilatometry experiments, and observe the
deflection of sintering beams using in situ imaging. These experiments show that the precursor
dramatically suppresses creep during sintering, demonstrating a potential solution for increasing
the dimensional accuracy of the binder jet 3D printing process.Mechanical Engineerin