Flux Tube Model Research Articles

The Mass and Decay Properties of the 1−+ Light Hybrid Meson

We calculate the complete form of the dimension-8 condensate contributions in the two-point correlator of the (1−+,0++) light hybrid current considering the operator mixing under renormalization. We find the inclusion these higher power corrections as well as the update of 〈g3G3〉 increase the QCD sum rule mass prediction for the 1−+ light hybrid. The obtained conservative mass range 1.72–2.60 GeV does not favor the π1(1400) and the π1(1600) to be pure hybrid states and suggests the π1(2015) observed by E852 is more likely to have much of a hybrid constituent. We also study the b1π and ρπ decay patterns of the 1−+ light hybrid with light-cone QCD sum rules. We obtain a relatively large partial decay width of the b1π mode, which is consistent with the predictions from the flux tube models and lattice QCD. More interestingly, using the tensor interpolating current we find the partial decay width of the ρπ mode is very small due to the lack of the leading twist contribution in the light-cone expansion of the correlation function.

Fluting Modes in Transversely Nonuniform Solar Flux Tubes

Abstract Magnetohydrodynamic waves of different types are frequently observed in magnetic flux tubes of the solar atmosphere and are often modeled using simple models. In the standard flux tube model made of a straight uniform tube with an abrupt boundary, transverse wave modes are classified according to their azimuthal wavenumber, m. Sausage (m = 0) and kink (m = 1) modes produce pulsations of the cross section and transverse oscillations of tube axis, respectively. Both sausage and kink modes have been observed in the solar atmosphere. Fluting ( ) modes produce perturbations that are essentially confined around the boundary of the tube, i.e., they have a strong surface-like character. Unlike sausage and kink modes, the detection of fluting modes remains elusive. Here we show that the inclusion of transverse inhomogeneity in the flux tube model dramatically affects the properties of fluting modes. Even in a thin tube, kink and fluting modes are no longer degenerate in frequency when the tube has a smooth boundary. In addition, fluting modes become heavily damped by resonant absorption in a timescale shorter than the oscillation period. The perturbations loose their global shape and their distinctive surface-like appearance. As a consequence of that, we argue that nonuniform flux tubes with smooth boundaries may not be able to support fluting-like perturbations as coherent, global modes.

Experimental investigation of plasma sheaths in magnetic mirror and cusp configurations

Sheath structures near a metal plate in a magnetized plasma were experimentally investigated in magnetic mirror and cusp configurations. Plasma parameters and the sheath potential distributions were probed by a planar and an emissive probe, respectively. The measured sheath profiles in the mirror configuration show that the sheath thickness first decreases and then increases when the magnetic strength is raised. A magnetic flux-tube model was used to explain this result. In the cusp configuration, the measured sheath thickness decreases with the increase of the coil current creating the magnetic cusp. However, when normalized by the electron Debye length, the dependence of the sheath thickness on the coil current is reversed.

An Efficient Design Optimization Framework for Nonlinear Switched Reluctance Machines

A new computationally efficient paradigm for the design and analysis of switched reluctance machines is proposed. At the heart of the rapid analysis and design methodology is the reduced-order computational method based on a flux-tube model, which has been refined and extended. It is demonstrated how the improved model enables consistent and accurate analysis and design optimization. Instead of an analytical derivation, an automatic generation of cubic splines is introduced to model the magnetic flux. The flux-linkage functions obtained from the improved flux-tube method indicate that the method offers good accuracy compared with the finite-element-based analysis, but with significantly improved computational efficiency. The approach is applicable to translating and rotating switched reluctance machines of various topologies, and therefore, enables rapid design search and optimization of novel topologies.

Investigation of Mass and Regge Trajectories of Heavy Pentaquarks

The higher state masses of the heavy pentaquarks ${\theta _{c}^{0}}, {N_{c}^{0}}, {{\Xi }_{c}^{0}}$ and $\theta _{b}^{+}, N_{b}^{+}, {\Xi }_{b}^{+}$ have been investigated in diquark-diquark-antiquark configuration where the lightquarks combine to form a diquark and the heavy quark (either charm or bottom) is the antiquark. Composite fermion model of quasi particle has been employed to describe the diquark. The states are investigated in the mass loaded flux tube model where two light diquarks are supposed to be linked by a flux tube to the heavy quark. The Regge trajectories (RTs) for heavy pentaquarks have also been analyzed. The Regge slope (α) of charm ( ${\theta _{c}^{0}}, {N_{c}^{0}}$ and $ {{\Xi }_{c}^{0}}$ ) and bottom ( $\theta _{b}^{+}, N_{b}^{+}$ and $ {\Xi }_{b}^{+}$ ) families are found to deviate from linearity condition with α a v e r a g e ≠1.1 G e V 2, the universal accepted value. The string tension (σ) have also been studied. The ground state masses of the pentaquarks have been extracted from (M 2,L) RT plot. Results are found to be in good agreement with results available in literature.

Solar Filament Longitudinal Oscillations along a Magnetic Field Tube with Two Dips

Abstract Large-amplitude longitudinal oscillations of solar filaments have been observed and explored for more than ten years. Previous studies are mainly based on the one-dimensional rigid flux tube model with a single magnetic dip. However, it has been noted that there might be two magnetic dips, and hence two threads, along one magnetic field line. Following previous work, we intend to investigate the kinematics of the filament longitudinal oscillations when two threads are magnetically connected, which is done by solving one-dimensional radiative hydrodynamic equations with the numerical code MPI-AMRVAC. Two different types of perturbations are considered, and the difference from previous works resulting from the interaction of the two filament threads is investigated. We find that even with the inclusion of the thread–thread interaction, the oscillation period is modified weakly, by at most 20% compared to the traditional pendulum model with one thread. However, the damping timescale is significantly affected by the thread–thread interaction. Hence, we should take it into account when applying the consistent seismology to the filaments where two threads are magnetically connected.

How large is the contribution of excited mesons in coupled-channel effects?

We study the excited $B$ mesons' contributions to the coupled-channel effects under the framework of ${}^3P_0$ model for the bottomonium. Contrary to what has been widely accepted, the contributions of $P$ wave $B$ mesons are generally the largest and this result is independent of the potential parameters to some extent. We also push the calculation beyond $B(1P)$ and carefully analyze the contributions of $B(2S)$. A form factor is a key ingredient to suppress the contributions of $B(2S)$ for low lying bottomonia. However, this suppression mechanism is not efficient for highly excited bottomonia such as $\Upsilon(5S)$ and $\Upsilon(6S)$. We give explanations why this difficulty happens to ${}^3P_0$ model and suggest analyzing flux-tube breaking model for the full calculation of coupled-channel effects.

Heavy pentaquark states and a novel color structure

Encouraged by the observation of the pentaquark states ${P}_{c}^{+}(4380)$ and ${P}_{c}^{+}(4450)$, we propose a novel color flux-tube structure, a pentagonal state, for pentaquark states within the framework of a color flux-tube mode involving a five-body confinement potential. Numerical results on the heavy pentaquark states indicate that the states with three color flux-tube structures, diquark, octet, and pentagonal structures, have the closest masses, which can therefore be called QCD isomers, analogous to isomers in chemistry. The pentagonal structure has the lowest energy. The state ${P}_{c}^{+}(4380)$ can be described as the compact pentaquark state $uudc\overline{c}$ with the pentagonal structure and ${J}^{P}={\frac{3}{2}}^{\ensuremath{-}}$ in the color flux-tube model. The state ${P}_{c}^{+}(4450)$ can not be accommodated into the color flux-tube model. The heavy pentaquark states $uudc\overline{b}$, $uudb\overline{c}$, and $uudb\overline{b}$ are predicted in the color flux-tube model. The five-body confinement potential, based on the color flux-tube picture as a collective degree of freedom, is a dynamical mechanism in the formation of the compact heavy pentaquark states.

A RECONNECTION-DRIVEN MODEL OF THE HARD X-RAY LOOP-TOP SOURCE FROM FLARE 2004 FEBRUARY 26

ABSTRACT A compact X-class flare on 2004 February 26 showed a concentrated source of hard X-rays at the tops of the flare’s loops. This was analyzed in previous work and interpreted as plasma heated and compressed by slow magnetosonic shocks (SMSs) generated during post-reconnection retraction of the flux. That work used analytic expressions from a thin flux tube (TFT) model, which neglected many potentially important factors such as thermal conduction and chromospheric evaporation. Here we use a numerical solution of the TFT equations to produce a more comprehensive and accurate model of the same flare, including those effects previously omitted. These simulations corroborate the prior hypothesis that slow-mode shocks persist well after the retraction has ended, thus producing a compact, loop-top source instead of an elongated jet, as steady reconnection models predict. Thermal conduction leads to densities higher than analytic estimates had predicted, and evaporation enhances the density still higher, but at lower temperatures. X-ray light curves and spectra are synthesized by convolving the results from a single TFT simulation with the rate at which flux is reconnected, as measured through motion of flare ribbons, for example. These agree well with light curves observed by RHESSI and GOES and spectra from RHESSI. An image created from a superposition of TFT model runs resembles one produced from RHESSI observations. This suggests that the HXR loop-top source, at least the one observed in this flare, could be the result of SMSs produced in fast reconnection models like Petschek’s.

Electromagnetic Casimir densities for a cylindrical shell on de Sitter space

Complete set of cylindrical modes is constructed for the electromagnetic field inside and outside a cylindrical shell in the background of [Formula: see text]-dimensional dS space–time. On the shell, the field obeys the generalized perfect conductor boundary condition. For the Bunch–Davies vacuum state, we evaluate the vacuum expectation values (VEVs) of the electric field squared and of the energy–momentum tensor. The shell-induced contributions are explicitly extracted. In this way, for points away from the shell, the renormalization is reduced to the one for the VEVs in the boundary-free dS bulk. As a special case, the VEVs are obtained for a cylindrical shell in the [Formula: see text]-dimensional Minkowski bulk. We show that the shell-induced contribution in the electric field squared is positive for both the interior and exterior regions. The corresponding Casimir–Polder forces are directed toward the shell. The vacuum energy–momentum tensor, in addition to the diagonal components, has a nonzero off-diagonal component corresponding to the energy flux along the direction normal to the shell. This flux is directed from the shell in both the exterior and interior regions. For points near the shell, the leading terms in the asymptotic expansions for the electric field squared and diagonal components of the energy–momentum tensor are obtained from the corresponding expressions in the Minkowski bulk replacing the distance from the shell by the proper distance in the dS bulk. The influence of the gravitational field on the local characteristics of the vacuum is essential at distances from the shell larger than the dS curvature radius. The results are extended for confining boundary conditions of flux tube models in QCD.

Revisiting theb1πandρπdecay modes of the1−+light hybrid state with light-cone QCD sum rules

We study the $\rho\pi$ and $b_1\pi$ decay modes of the $1^{-+}$ light hybrid state within the framework of light-cone QCD sum rules. We use both the tensor current $\bar\psi\sigma_{\mu\nu}\psi$ and the derivative current $\bar{\psi}\overleftrightarrow{D}_\mu\gamma_5\psi$ as interpolating currents to calculate the partial decay width of the $b_1\pi$ decay mode. Comparing the sum rules obtained by using different currents, we obtain $\Gamma(\pi_1\to b_1\pi)$ = 8--23, 32--86 and 52--151\,MeV for $m_{1^{-+}}$ = 1.6, 1.8 and 2.0\,GeV respectively, which favour the results from the flux tube models and lattice simulations. We also use the tensor current to study the $\rho\pi$ decay mode, and although an extended stability criterion is needed, our results suggest a small partial decay width.

Neutral and non-neutral collisionless plasma equilibria for twisted flux tubes: The Gold-Hoyle model in a background field

We calculate exact one-dimensional collisionless plasma equilibria for a continuum of flux tube models, for which the total magnetic field is made up of the “force-free” Gold-Hoyle magnetic flux tube embedded in a uniform and anti-parallel background magnetic field. For a sufficiently weak background magnetic field, the axial component of the total magnetic field reverses at some finite radius. The presence of the background magnetic field means that the total system is not exactly force-free, but by reducing its magnitude, the departure from force-free can be made as small as desired. The distribution function for each species is a function of the three constants of motion; namely, the Hamiltonian and the canonical momenta in the axial and azimuthal directions. Poisson's equation and Ampère's law are solved exactly, and the solution allows either electrically neutral or non-neutral configurations, depending on the values of the bulk ion and electron flows. These equilibria have possible applications in various solar, space, and astrophysical contexts, as well as in the laboratory.

Comparison of gradient and flux driven gyro-kinetic turbulent transport

Flux and gradient driven ion temperature gradient turbulence in tokamak geometry and for Cyclone base case parameters are compared in the local limit using the same underlying gyro-kinetic turbulence model. The gradient driven turbulence described using the flux tube model with periodic boundary conditions has a finite ion heat flux Qi≈10n0T0ρ*2vth, where n0 (T0) is the background density (temperature), ρ*=ρ/R is the normalized Larmor radius, R is the major radius of the device, and vth is the ion thermal velocity at the nonlinear threshold of the temperature gradient length for turbulence generation. Consequently, the gradient driven local transport model is unable to accurately describe heat fluxes below Qi<10n0T0ρ*2vth, since no stationary fully developed turbulent state can be obtained. The turbulence in the flux driven case shows intermittent behaviour and avalanches for Qi<10n0T0ρ*2vth. Isolated avalanches disappear for Qi>10n0T0ρ*2vth, and at higher heat fluxes, the statistics of the turbulence is the same for the flux and gradient driven case. The nonlinear upshift of the temperature gradient length threshold for turbulence generation (known as the Dimits shift) is larger in the case of flux driven turbulence. This higher nonlinear upshift is attributed to the generation of structures in the radial temperature profile, known as staircases [Dif-Pradalier, Phys. Rev. E 82, 025401 (2010)]. Avalanches are initiated at specific locations and have roughly the same radial extent of 50–70 ion Larmor radii. The staircases are obtained at low heating rates, and become unstable and break up at higher heating rates. At the heat fluxes for which staircase formation is observed, no stationary gradient driven simulations can be obtained.

Regge trajectories of exotic hadrons in the flux tube model

We have investigated the Regge trajectories of exotic hadrons by considering different possible pentaquark configurations with finite quark mass in the flux tube model. Significant deviation is observed in the linear behavior of the Regge trajectories for pentaquark systems in view of the universal value of the Regge slope parameter for hadrons. The modified Regge trajectories are also compared with the available experimental and lattice data. It is observed that the nonlinear Regge trajectories of such pentaquark systems can be well described by the relativistic corrections in view of the current quark masses and the high rotational speed of the quarks at the end of flux tube structure.

N-body model of magnetic flux tubes reconnecting in the solar atmosphere

The investigation of dynamics of the small scale magnetic field on the Sun photosphere is necessary to understand the physical processes occurring in the higher layers of solar atmosphere due to the magnetic coupling between the photosphere and the corona. We present a simulation able to address these phenomena investigating the statistics of magnetic loops reconnections. The simulation is based on N-body model approach and is divided in two computational layers. We simplify the convection problem, interpreting the larger convective scale, mesogranulation, as the result of the collective interaction of convective downflow of granular scale. The N-body advection model is the base to generate a synthetic time series of nanoflares produced by interacting magnetic loops. The reconnection of magnetic field lines is the result of the advection of the magnetic footpoints following the velocity field generated by the interacting downflows. The model gives a quantitative idea of how much energy is expected to be released by the reconfiguration of magnetic loops in the quiet Sun.

Identification of Y (4008), Y (4140), Y (4260), and Y (4360) as Tetraquark States**Supported by the National Natural Science Foundation of China under Grant Nos 11305274, 11175088 and 11035006, and the Chongqing Natural Science Foundation under Grant No cstc2013jcyjA00014.

Within the framework of a color flux-tube model with a four-body confinement potential, the tetraquark states [cq][c¯q¯] (q = u or d) with I JPC = 01− − are systematically investigated. The numerical results indicate that states Y (4008), Y (4140), Y (4260), and Y (4360) can be uniformly described as tetraquark states [cq][c¯q¯] with n2S+1 LJ of 11 P1, 15 P1, 25 P1 and 15F1, respectively, in the color flux-tube model. They are compact three-dimensional spatial configurations similar to a rugby ball, higher orbital angular momentum L, more prolate. The four-body confinement interaction based on a color flux-tube picture should be responsible for the formation of those compact tetraquark states.

Three-dimensional non-LTE radiative transfer effects in Fe i lines

Non-local thermodynamic equilibrium (NLTE) effects in diagnostically important solar Fe I lines are important due to the strong sensitivity of Fe I to ionizing UV radiation, which may lead to a considerable under-population of the Fe I levels in the solar atmosphere and, therefore, to a sizeable weakening of Fe I lines. Such NLTE effects may be intensified or weakened by horizontal radiative transfer (RT) in a three-dimensionally (3-D) structured atmosphere. We analyze the influence of horizontal RT on commonly used Fe I lines in a snapshot of a 3-D radiation magneto-hydrodynamic (MHD) simulation of a plage region. NLTE- and horizontal RT effects occur with considerable strength (up to 50% in line depth or equivalent width) in the analyzed snapshot. As they may have either sign and both signs occur with approximately the same frequency and strength, the net effects are small when considering spatially averaged quantities. The situation in the plage atmosphere turns out to be rather complex. Horizontal transfer leads to line-weakening relative to 1-D NLTE transfer near the boundaries of kG magnetic elements. Around the centers of these elements, however, we find an often significant line-strengthening. This behavior is in contrast to that expected from previous 3-D RT computations in idealized flux-tube models, which display only a line weakening. The origin of this unexpected behavior lies in the fact that magnetic elements are surrounded by dense and relatively cool down-flowing gas, which forms the walls of the magnetic elements. The continuum in these dense walls is often formed in colder gas than in the central part of the magnetic elements. Consequently, the central parts of the magnetic element experience a sub-average UV-irradiation leading to the observed 3-D NLTE line strengthening.

Systematic study ofZc+family from a multiquark color flux-tube model

Inspired by the present experimental status of charged charmonium-like states $Z_c^+$, the tetraquark states $[cu][\bar{c}\bar{d}]$ are systematically studied in a color flux-tube model with a multi-body confinement potential. The investigation indicates that charged charmonium-like states $Z_c^+(3900)$ or $Z_c^+(3885)$, $Z_c^+(3930)$, $Z_c^+(4020)$ or $Z_c^+(4025)$, $Z_1^+(4050)$, $Z_2^+(4250)$, and $Z_c^+(4200)$ can be uniformly described as tetraquark states $[cu][\bar{c}\bar{d}]$ with the quantum numbers $n^{2S+1}L_J$ and $J^P$ of $1^{3}S_1$ and $1^+$, $2^{3}S_1$ and $1^+$, $1^5S_2$ and $2^+$, $1^3P_1$ and $1^-$, $1^5D_1$ and $1^+$, and $1^3D_1$ and $1^+$, respectively. The predicted lowest charged tetraquark state $[cu][\bar{c}\bar{d}]$ with $0^+$ and $1^1S_0$ has a energy of $3780\pm10$ MeV in the model. The tetraquark states are compact three-dimensional spatial configurations similar to a rugby ball, the higher orbital angular momentum $L$ between the diquark $[cu]$ and antidiquark $[\bar{c}\bar{d}]$, the more prolate of the states. The multibody color flux-tube, a collective degree of freedom, plays an important role in the formation of those charge tetraquark states. However, the two heavier charged states $Z^+_c(4430)$ and $Z^+_c(4475)$ can not be explained as tetraquark states $[cu][\bar{c}\bar{d}]$ in this model approach.

Investigation of ΛQ and ΞQ baryons in the heavy quark-light diquark picture

We apply a new mass formula which is derived analytically in the relativistic flux tube model to the mass spectra of $\Lambda_Q$ and $\Xi_Q$ (\emph{Q} = \emph{c} or \emph{b} quark) baryons. To this end, the heavy quark-light diquark picture is employed. We find that all masses of the available $\Lambda_Q$ and $\Xi_Q$ states can be understood well. The assignments to these states do not appear to contradict the strong decay properties. $\Lambda_c(2760)^+$ and $\Xi_c(2980)$ are assigned to the first radial excitations with $J^P = 1/2^+$. $\Lambda_c(2940)^+$ and $\Xi_c(3123)$ might be the 2\emph{P} states. The $\Lambda_c(2880)^+$ and $\Xi_c(3080)$ are the good 1\emph{D} candidates with $J^P = 5/2^+$. $\Xi_c(3055)$ is likely to be a 1\emph{D} state with $J^P = 3/2^+$. $\Lambda_b(5912)^0$ and $\Lambda_b(5920)^0$ favor the 1\emph{P} assignments with $J^P = 1/2^-$ and $3/2^-$, respectively. We propose a search for the $\tilde{\Lambda}_{c2}(5/2^-)$ state which can help to distinguish the diquark and three-body schemes.

Energy and energy flux in axisymmetric slow and fast waves

Aims. We aim to calculate the kinetic, magnetic, thermal, and total energy densities and the flux of energy in axisymmetric saus age modes. The resulting equations should contain as few parameters as possible to facilitate applicability for di fferent observations. Methods. The background equilibrium is a one-dimensional cylindrical flux tube model with a piecewise constant radial density profile. This enables us to use linearised magnetohydrodyna mic equations to calculate the energy densities and the flux o f energy for axisymmetric sausage modes. Results. The equations used to calculate the energy densities and the flux of energy in axisymmetric sausage modes depend on the