Compressive high-frequency waves riding on an Alfv\'en/ion-cyclotron wave in a multi-fluid plasma

In this paper, we study the weakly-compressive high-frequency plasma waves which are superposed on a large-amplitude Alfv\'en wave in a multi-fluid plasma consisting of protons, electrons, and alpha particles. For these waves, the plasma environment is inhomogenous due to the presence of the low-frequency Alfv\'en wave with a large amplitude, a situation that may apply to space plasmas such as the solar corona and solar wind. The dispersion relation of the plasma waves is determined from a linear stability analysis using a new eigenvalue method that is employed to solve the set of differential wave equations which describe the propagation of plasma waves along the direction of the constant component of the Alfv\'en wave magnetic field. This approach also allows one to consider weak compressive effects. In the presence of the background Alfv\'en wave, the dispersion branches obtained differ significantly from the situation of a uniform plasma. Due to compressibility, acoustic waves are excited and couplings between various modes occur, and even an instability of the compressive mode. In a kinetic treatment, these plasma waves would be natural candidates for Landau-resonant wave-particle interactions, and may thus via their damping lead to particle heating.Comment: 15 pages, 5 figure

On nonlinear Alfv\'en-cyclotron waves in multi-species plasma

Large-amplitude Alfv\'en waves are ubiquitous in space plasmas and a main component of magnetohydrodynamic (MHD) turbulence in the heliosphere. As pump waves they are prone to parametric instability by which they can generate cyclotron and acoustic daughter waves. Here we revisit a related process within the framework of the multi-fluid equations for a plasma consisting of many species. The nonlinear coupling of the Alfv\'en wave to acoustic waves is studied, and a set of compressive and coupled wave equations for the transverse magnetic field and longitudinal electric field is derived for waves propagating along the mean-field direction. It turns out that slightly compressive Alfv\'en waves exert, through induced gyro-radius and kinetic-energy modulations, an electromotive force on the particles in association with a longitudinal electric field, which has a potential that is given by the gradient of the transverse kinetic energy of the particles gyrating about the mean field. This in turn drives electric fluctuations (sound and ion-acoustic waves) along the mean magnetic field, which can nonlinearly react back on the transverse magnetic field. Mutually coupled Alfv\'en-cyclotron-acoustic waves are thus excited, a nonlinear process that can drive a cascade of wave energy in the plasma and may generate compressive microturbulence. These driven electric fluctuations might have consequences for the dissipation of MHD turbulence and, thus, for the heating and acceleration of particles in the solar wind.Comment: 19 pages, accepted by Journal of Plasma Physics, in press, Link: http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=7908294&fulltextType=RA&fileId=S002237781000054

The coronal convection

We study the hydrogen Lyman emission in various solar features - now including Lyman-alpha observations free from geocoronal absorption - and investigate statistically the imprint of flows and of the magnetic field on the line profile and radiance distribution. As a new result, we found that in Lyman-alpha rasters locations with higher opacity cluster in the cell interior, while the network has a trend to flatter profiles. Even deeper self reversals and larger peak distances were found in coronal hole spectra. We also compare simultaneous Lyman-alpha and Lyman-beta profiles. There is an obvious correspondence between asymmetry and redshift for both lines, but, most surprisingly, the asymmetries of Lyman-alpha and Lyman-beta are opposite. We conclude that in both cases downflows determine the line profile, in case of Lyman-alpha by absorption and in the case of Ly-beta by emission. Our results show that the magnetically structured atmosphere plays a dominating role in the line formation and indicate the presence of a persisting downflow at both footpoints of closed loops. We claim that this is the manifestation of a fundamental mass transportation process, which Foukal back in 1978 introduced as the 'coronal convection'.Comment: 8 pages, 5 figures, accepted for publication in Cent. Eur. Astrophys. Bul

Upflows in funnel-like legs of coronal magnetic loops

The prominent blue shifts of Ne viii associated with the junctions of the magnetic network in the quiet Sun are still not well understood. By comparing the coronal magnetic-field structures as obtained by a potential-field reconstruction with the conspicuous blue-shift patches on the dopplergram of Ne viii as observed in an equatorial quiet-Sun region, we find that most of the regions with significant upflow are associated with the funnel-like legs of magnetic loops and co-spatial with increments of the line width. These quasi-steady upflows can be regarded as the signatures of mass supply to coronal loops. By using the square-root of the line intensity as a proxy for the plasma density, the mass flux of the upflow in each funnel can be estimated. We find that the mass flux is anti-correlated with the funnel's expansion factor as determined from the extrapolated magnetic field. One of the loop systems is associated with a coronal bright point, which was observed by several instruments and exhibited various morphologies in different wavelengths and viewing directions. A remarkable agreement between its magnetic structure and the associated EUV emission pattern was found, suggesting an almost potential-field nature of the coronal magnetic field. We also report the direct detection of a small-scale siphon flow by both STEREO satellites. However, this transient siphon flow occurred in a weak mixed-polarity-field region, which was outside the adjacent magnetic funnel, and thus it is perhaps not related to plasma upflow in the funnel. Based on these observations, we suggest that at upper-TR temperatures the dominant flows in quiet-Sun coronal loops are long-lasting upflows rather than siphon flows. We also discuss the implications for coronal heating and unresolved magnetic structures.Comment: 20 pages, 5 figures, accepted by Ap

Cool and hot components of a coronal bright point

We performed a systematic study of the Doppler shifts and electron densities measured in an EUV bright point (hereafter BP) observed in more than 10 EUV lines with formation temperatures from log (T/K) p 4.5 to 6.3. Those parts of a BP seen in transition region and coronal lines are defined as its cool and hot components, respectively. We find that the transition from cool to hot occurs at a temperature around log (T/K) p 5.7. The two components of the BP reveal a totally different orientation and Doppler-shift pattern, which might result from a twist of the associated magnetic loop system. The analysis of magnetic field evolution and topology seems to favor a two-stage heating process, in which magnetic cancellation and separator reconnection are powering, respectively, the cool and hot components of the BP. We also found that the electron densities of both components of the BP are higher than those of the surrounding quiet Sun, and comparable to or smaller than active region densities.Comment: 4 pages, 4 figure

On isospin and flavour of leptons and quarks

Isospin emerges naturally from the Lorentz transformation of spinors, if they are based on the vector representation of the Lorentz group. The resulting extended Dirac equation for a massive spin-one-half fermion has two new additional degrees of freedom associated with the up and down components of isospin. This doublet is interpreted as describing the electron and neutrino. It is adjoined with the SU(2) symmetry group. The extended Dirac equation appears in six versions which are connected by similarity transformations. It is argued that this trait may explain the occurrence of the three families of the leptons and suggested that flavour arises genuinely from the algebraic properties of the extended Dirac equation. Its solutions are discussed and the physical role of isospin is elucidated. Isospin symmetry can be gauged, which leads to a weak-interaction-type theory and is valid for finite initial mass. Breaking the isospin SU(2) symmetry yields the correct electric charges of the particles by means of the electroweak unification procedures of the standard model

Fundamental Fermion Interactions via Vector Bosons of Unified SU(2)⊗SU(4) Gauge Fields

Employing the fermion unification model based on the intrinsic SU(8) symmetry of a generalized Dirac equation, we discuss the fundamental interactions under the SU(8) = SU(2) ⊗ SU(4) symmetry group. The physics involved can describe all fermions, the leptons (electron and neutrino), and the colored up and down quarks of the first generation in the standard model (SM) by a complex SU(8) octet of Dirac spinor fields. The fermion interactions are found to be mediated by the unified SU(4) and SU(2) vector gauge boson fields, which include the photon, the gluons, and the bosons Z and W as well known from the SM, but also comprise new ones, namely three colored X bosons carrying a fractional hypercharge of ± 4/3 and transmuting leptons into quarks and vice versa. The full covariant derivative of the model is derived and discussed. The Higgs mechanism gives mass to the Z and W bosons, but also permits one to derive the mass of the colored X boson, for which depending on the choice of the values of the coupling constant, the estimates are 35 or 156 GeV, values that are well within reach of the LHC. The scalar Higgs field can also lend masses to the fermions and fix their physical values for given appropriate coupling constants to that field

Correction to: On isospin and flavour of leptons and quarks

Isospin emerges naturally from the Lorentz transformation of spinors, if they are based on the vector representation of the Lorentz group. The resulting extended Dirac equation for a massive spin-one-half fermion has two new additional degrees of freedom associated with the up and down components of isospin. This doublet is interpreted as describing the electron and neutrino. It is adjoined with the SU(2) symmetry group. The extended Dirac equation appears in six versions which are connected by similarity transformations. It is argued that this trait may explain the occurrence of the three families of the leptons and suggested that flavour arises genuinely from the algebraic properties of the extended Dirac equation. Its solutions are discussed and the physical role of isospin is elucidated. Isospin symmetry can be gauged, which leads to a weak-interaction-type theory and is valid for finite initial mass. Breaking the isospin SU(2) symmetry yields the correct electric charges of the particles by means of the electroweak unification procedures of the standard model