6,622 research outputs found
Euler potentials for the MHD Kamchatnov-Hopf soliton solution
In the MHD description of plasma phenomena the concept of magnetic helicity
turns out to be very useful. We present here an example of introducing Euler
potentials into a topological MHD soliton which has non-trivial helicity. The
MHD soliton solution (Kamchatnov, 1982) is based on the Hopf invariant of the
mapping of a 3D sphere into a 2D sphere; it can have arbitrary helicity
depending on control parameters. It is shown how to define Euler potentials
globally. The singular curve of the Euler potential plays the key role in
computing helicity. With the introduction of Euler potentials, the helicity can
be calculated as an integral over the surface bounded by this singular curve. A
special programme for visualization is worked out. Helicity coordinates are
introduced which can be useful for numerical simulations where helicity control
is needed.Comment: 15 pages, 12 figure
Crossed channel analysis of quark and gluon generalized parton distributions with helicity flip
Quark and gluon helicity flip generalized parton distributions (GPDs) address
the transversity quark and gluon structure of the nucleon. In order to
construct a theoretically consistent parametrization of these hadronic matrix
elements, we work out the set of combinations of those GPDs suitable for the
partial wave (PW) expansion in the cross-channel. This universal
result will help to build up a flexible parametrization of these important
hadronic non-perturbative quantities, using for instance the approaches based
on the conformal PW expansion of GPDs such as the Mellin-Barnes integral or the
dual parametrization techniques.Comment: 34 pages, 1 figure, 4 table
Toward modelization of quark and gluon transversity generalized parton distributions
Quark and gluon helicity flip generalized parton distributions (GPDs) encode
the information on the nucleon structure in the transversity sector. In order
to build a theoretically consistent phenomenological parametrization for these
hadronic matrix element within the framework of the dual parametrization of
GPDs (or with the equivalent approach of the SO(3) partial waves (PW) expansion
with the Mellin-Barnes integral techniques) we establish the set of
combinations of parton helicity flip GPDs suitable for the expansion in the
cross channel SO(3) PWs.Comment: 6 pages, DIS 2014, XXII. International Workshop on Deep-Inelastic
Scattering and Related Subjects, 28 April - 2 May 2014, Warsaw, Polan
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