Magnetic spiral structures can exhibit ferroelectric moments as recently demonstrated in various multiferroic materials. In such case the helicity of the magnetic spiral is directly correlated with the direction of the ferroelectric moment and measurement of the helicity of magnetic structures is of current interest. We used soft x-ray resonant diffraction with circular polarized incident radia...

The subgrid-scale (SGS) modeling of helical, isotropic turbulence in large eddy simulation is investigated by quantifying rates of helicity and energy cascade. Assuming Kolmogorov spectra, the Smagorinsky model with its traditional coefficient is shown to underestimate the helicity dissipation rate by about 40%. Several two-term helical models are proposed with the model coefficients calculated...

Aims. We investigate the instability of toroidal magnetic fields resulting by the action of z-dependent differential rotation on a given axial field B 0 in a cylindrical enclosure where in particular the helicity of the resulting nonaxisymmetric flow is of interest. The idea is probed that helicity is related to the external field and the differential rotation as H ∝ B 0 i B 0 j Ω i, j. Methods...

We examine multiphoton production in the electroweak sector of the Standard Model in the high energy limit using the equivalence theorem in combination with spinor helicity techniques. We utilize currents consisting of a charged scalar, spinor, or vector line that radiates n photons. Only one end of the charged line is off shell in these currents, which are known for the cases of like-helicity ...

We consider the magnetic helicity balance for the galactic dynamo in the framework of the local dynamo problem, as well as in the no-z model (which includes explicitly the radial distribution of the magnetic fields). When calculating the magnetic helicity balance we take into account the redistribution of the small-scale and large-scale magnetic fields between the magnetic helicities, as well a...

We calculate helicities of solar active regions based on the idea that poloidal flux lines get wrapped around a toroidal flux tube rising through the convection zone, thereby giving rise to the helicity. Rough estimates based on this idea compare favorably with the observed magnitude of helicity. We use our solar dynamo model based on the Babcock-Leighton a-effect to study how helicity varies w...

Large scale dynamos produce small scale current helicity as a waste product that quenches the large scale dynamo process (alpha effect). This quenching can be catastrophic (i.e., intensify with magnetic Reynolds number) unless one has fluxes of small scale magnetic (or current) helicity out of the system. We derive the form of helicity fluxes in turbulent dynamos, taking also into account the n...

The interaction between two side-by-side solar prominence-like plasmas has been studied using a four-electrode magnetized plasma source that can impose a wide variety of surface boundary conditions. When the source is arranged to create two prominences with the same helicity ~co-helicity!, it is observed that helicity transfer from one prominence to the other causes the receiving prominence to ...

The relation of magnetic helicity to the topological structure of field lines is discussed. If space is divided into a collection of flux tubes, magnetic helicity arises from internal structure within a flux tube, such as twist and kinking, and external relations between flux tubes, i.e. linking and knotting. The concepts of twist number and writhing number are introduced from the mathematical-...

Recent data for the ratio R(Q) = QF2(Q )/F1(Q ) shocked the community by disobeying expectations held for 50 years. We examine the status of perturbative QCD predictions for helicity-flip form factors. Contrary to common belief, we find there is no rule of hadron helicity conservation for form factors. Instead the analysis yields an inequality that the leading power of helicity-flip processes m...