During reconnection, a flux pileup region (FPR) is formed behind a dipolarization front in an outflow jet. Inside the FPR, the magnetic field magnitude and Bz component increase and the whistler‐mode ...waves are observed frequently. As the FPR convects toward the Earth during substorms, it is obstructed by the dipolar geomagnetic field to form a near‐Earth FPR. Unlike the structureless emissions inside the tail FPR, we find that the whistler‐mode waves inside the near‐Earth FPR can exhibit a discrete structure similar to chorus. Both upper band and lower band chorus are observed, with the upper band having a larger propagation angle (and smaller wave amplitude) than the lower band. Most chorus elements we observed are “rising‐tone” type, but some are “falling‐tone” type. We notice that the rising‐tone chorus can evolve into falling‐tone chorus within <3 s. One of the factors that may explain why the waves are unstructured inside the tail FPR but become discrete inside the near‐Earth FPR is the spatial inhomogeneity of magnetic field: we find that such inhomogeneity is small inside the near‐Earth FPR but large inside the tail FPR.
Key Points
Near‐Earth FPR: structured chorus; midtail FPR: unstructured whistlersSpatial inhomogeneity of magnetic field can explain such phenomenonRising‐tone chorus can evolve into falling‐tone chorus within <3 s
A symmetry-preserving approach to the two valence-body continuum bound-state problem is used to calculate the elastic electromagnetic form factors of the ρ-meson and subsequently to study the ...evolution of vector-meson form factors with current-quark mass. To facilitate a range of additional comparisons, K* form factors are also computed. The analysis reveals that vector mesons are larger than pseudoscalar mesons; composite vector mesons are nonspherical, with magnetic and quadrupole moments that deviate ∼30% from point-particle values; in many ways, vector-meson properties are as much influenced by emergent mass as those of pseudoscalars; and vector-meson electric form factors possess a zero at spacelike momentum transfer. Qualitative similarities between the electric form factors of the ρ and the proton, GEp, are used to argue that the character of emergent mass in the Standard Model can force a zero in GEp. Moreover, the existence of a zero in vector-meson electric form factors entails that a single-pole vector-meson dominance model can only be of limited use in estimating properties of off-shell vector mesons, providing poor guidance for systems in which the Higgs mechanism of mass generation is dominant.
Electroproduction form factors describing the γ*p→Δ+(1232), Δ+(1600) transitions are computed using a fully dynamical diquark-quark approximation to the Poincaré-covariant three-body bound-state ...problem in relativistic quantum field theory. In this approach, the Δ(1600) is an analogue of the Roper resonance in the nucleon sector, appearing as the simplest radial excitation of the Δ(1232). Precise measurements of the γ*p→Δ+(1232) transition already exist on 0≤Q2≲8 GeV2, and the calculated results compare favorably with the data outside the meson-cloud domain. The predictions for the γ*p→Δ+(1600) magnetic dipole and electric quadrupole transition form factors are consistent with the empirical values at the real photon point, and extend to Q2≈6mp2, enabling a meaningful direct comparison with experiment once analysis of existing data is completed. In both cases, the electric quadrupole form factor is particularly sensitive to deformation of the Δ-baryons. Interestingly, while the γ*p→Δ+(1232) transition form factors are larger in magnitude than those for γ*p→Δ+(1600) in some neighborhood of the real photon point, this ordering is reversed on Q2≳2mp2, suggesting that the γ*p→Δ+(1600) transition is more localized in configuration space.
A class of Polyakov-loop-modified Nambu–Jona-Lasinio models has been used to support a conjecture that numerical simulations of lattice-regularized QCD defined with a chiral chemical potential can ...provide information about the existence and location of a critical end point in the QCD phase diagram drawn in the plane spanned by baryon chemical potential and temperature. That conjecture is challenged by conflicts between the model results and analyses of the same problem using simulations of lattice-regularized QCD (lQCD) and well-constrained Dyson-Schwinger equation (DSE) studies. We find the conflict is resolved in favor of the lQCD and DSE predictions when both a physically motivated regularization is employed to suppress the contribution of high-momentum quark modes in the definition of the effective potential connected with the Polyakov-loop-modified Nambu–Jona-Lasinio models and the four-fermion coupling in those models does not react strongly to changes in the mean field that is assumed to mock-up Polyakov-loop dynamics. With the lQCD and DSE predictions thus confirmed, it seems unlikely that simulations of lQCD with μ5>0 can shed any light on a critical end point in the regular QCD phase diagram.
We present a statistical study of plasmaspheric plumes and ionospheric outflows observed by the Cluster spacecraft near the dayside magnetopause. Plasmaspheric plumes are identified when the ...low‐energy ions (<1 keV) with ∼90° pitch angle distributions are observed by the Cluster Ion Spectrometer/Hot Ion Analyzer instrument. The ionospheric outflows are characterized by unidirectional or bidirectional field‐aligned pitch angle distributions of low‐energy ions observed in the dayside magnetosphere. Forty‐three (10%) plasmaspheric plume events and 32 (7%) ionospheric outflow events were detected out of the 442 times that C3 crossed the dayside magnetopause between 2007 and 2009. The occurrence rate of plumes at duskside is significantly higher than that at dawnside. The occurrence rate of outflows shows a weak dawn‐dusk asymmetry. We investigate the dependence of the occurrence rates of plumes and ionospheric outflows on geomagnetic activity and on solar wind/interplanetary magnetic field (IMF) conditions. The plume events tend to occur during southward IMF (duskward solar wind electric field) and moderate geomagnetic activity (Kp = 3,−30≤Dst <− 10 nT). However, the ionospheric outflow events tend to occur during northward IMF (dawnward solar wind electric field). The ionospheric outflows do not occur when Kp = 0, and the occurrence rate of the ionospheric outflows does not have a clear Dst dependence. Seventy‐five percent (46%) of the outflows are observed in the duskside for negative (positive) IMF By. Conversely, 54% (25%) of the outflows are observed in the dawnside for positive (negative) IMF By. Finally, the occurrence rates of both plumes and outflows increase with solar wind dynamic pressure.
Key Points
Statistical study for plumes and ionospheric outflows observed by Cluster near the magnetopause
Plumes (outflows) tend to occur during southward (northward) IMF and moderate geomagnetic activity
Enhanced occurrence rates of outflows were observed in the dawnside (duskside) for IMF By > 0 (By < 0)
A symmetry-preserving truncation of the two-body light-quark bound-state problem in relativistic quantum field theory is used to calculate the leading-twist parton distribution amplitudes (PDAs) of ...scalar systems, both ground-state and radial excitations, and the radial excitations of vector mesons. Owing to the fact that the scale-independent leptonic decay constant of a scalar meson constituted from equal-mass valence constituents vanishes, it is found that the PDA of a given scalar system possesses one more zero than that of an analogous vector meson. Consequently, whereas the mean light-front relative momentum of the valence constituents within a vector meson is zero, that within a scalar meson is large, an outcome which hints at a greater role for light-front angular momentum in systems classified as P-wave in quantum mechanical models. Values for the scale-dependent decay constants of ground-state scalar and vector systems are a by-product of this analysis, and they turn out to be roughly equal, viz. ≃0.2 GeV at an hadronic scale. In addition, it is confirmed that the dilation characterizing ground-state PDAs is manifest in the PDAs of radial excitations too. The impact of SU(3)-flavor symmetry breaking is also considered. When compared with pseudoscalar states, it is a little stronger in scalar systems, but the size is nevertheless determined by the flavor dependence of dynamical chiral symmetry breaking and the PDAs are still skewed toward the heavier valence quark in asymmetric systems.
A tunable stiffness and damping vibration isolator based on magnetorheological elastomers (MREs) is developed. In this isolator, four MRE elements are used as the tunable springs, whose stiffness can ...be controlled by varying the magnetic field. A voice coil motor, which is controlled by the relative velocity feedback of the payload, is used as the tunable damper of the isolator. Under the combined ON–OFF control, the proposed vibration isolator shows satisfying isolation effect. The experimental results indicate that the responses of the payload are suppressed significantly in comparison to the passive system. The transmissibility of the payload around the resonant frequency is decreased by 61.5%. The root mean square (RMS) value and the maximum value of the displacement responses of the payload are decreased by 36.0% and 50.0%, respectively. In addition, the RMS values and maximum values of the velocity responses are decreased by 45.4% and 52.5%, respectively.
An important source of the terrestrial magnetospheric plasma is the Earth's ionospheric outflows from the high‐latitude regions of both hemispheres. The ionospheric ion outflows have rarely been ...observed at the dayside magnetopause. We report Cluster observations of the ionospheric ion outflows observed at the dayside magnetopause. The low‐energy (up to 1.5 keV) electrons are detected with bidirectional pitch angle distributions indicating that the magnetic field lines are closed. The unidirectional cold ions (< 200 eV) are observed in the magnetosphere by both C1 and C3. The pitch angle distributions (0∘–75∘) of the cold ions (< 1 keV) at the dayside magnetopause indicate that these cold ions are the ionospheric outflows coming only from the Southern Hemisphere. The cold ions (< 200 eV) fluxes are modulated by the ULF wave electric field. Two different species (possibly H+ and He+) are observed in the magnetosphere. Our results suggest that the ionospheric outflows can directly reach the dayside magnetopause region and may participate in the reconnection process.
Key Points
The unidirectional cold ions (<200 eV) are observed at the dayside magnetopause
The cold ions are the ionospheric outflow coming from the Southern Hemisphere
The cold ion fluxes are modulated by the ULF wave electric field
The factors controlling asymmetric reconnection and the role of the cold plasma population in the reconnection process are two outstanding questions. We present a case study of multipoint Cluster ...observations demonstrating that the separatrix and flow boundary angles are greater on the magnetosheath than on the magnetospheric side of the magnetopause, probably due to the stronger density than magnetic field asymmetry at this boundary. The motion of cold plasmaspheric ions entering the reconnection region differs from that of warmer magnetosheath and magnetospheric ions. In contrast to the warmer ions, which are probably accelerated by reconnection in the diffusion region near the subsolar magnetopause, the colder ions are simply entrained by E×B drifts at high latitudes on the recently reconnected magnetic field lines. This indicates that plasmaspheric ions can sometimes play only a very limited role in asymmetric reconnection, in contrast to previous simulation studies. Three cold ion populations (probably H+, He+, and O+) appear in the energy spectrum, consistent with ion acceleration to a common velocity.
Key Points
The cold ions (H+, He+, and O+) are picked up by the reconnected magnetic field
The cold ions are accelerated perpendicular to the magnetic field
Asymmetric reconnection geometry is caused by the stronger asymmetry in density
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