The Sagdeev potential technique has been used to investigate the existence
and the polarity of dust ion acoustic solitary structures in an unmagnetized
collisionless nonthermal dusty plasma consisting of negatively charged static
dust grains, adiabatic warm ions and nonthermal electrons when the velocity of
the wave frame is equal to the linearized velocity of the dust ion acoustic
wave for long wave length plane wave perturbation, i.e., when the velocity of
the solitary structure is equal to the acoustic speed. A compositional
parameter space has been drawn which shows the nature of existence and the
polarity of dust ion acoustic solitary structures at the acoustic speed. This
compositional parameter space clearly indicates the regions for the existence
of positive and negative potential dust ion acoustic solitary structures.
Again, this compositional parameter space shows that the present system
supports the negative potential double layer at the acoustic speed along a
particular curve in the parametric plane. However, the negative potential
double layer is unable to restrict the occurrence of all negative potential
solitary waves. As a result, in a particular region of the parameter space,
there exist negative potential solitary waves after the formation of negative
potential double layer. But the amplitudes of these supersolitons are bounded.
A finite jump between amplitudes of negative potential solitons separated by
the negative potential double layer has been observed, and consequently, the
present system supports the supersolitons at the acoustic speed in a
neighbourhood of the curve along which negative potential double layer exist.
The effects of the parameters on the amplitude of the solitary structures at
the acoustic speed have been discussed.

The influence of non-Maxwellian ions on the ion-dust streaming instability in a complex plasma is investigated. The ion susceptibility employed for the calculations self-consistently accounts for the acceleration of the ions by a homogeneous background electric field and their collisions with neutral gas particles via a Bhatnagar-Gross-Krook collision term [e.g., A. V. Ivlev et al., Phys. Rev. E 71, 016405 (2005)], leading to significant deviations from a shifted Maxwellian distribution. The dispersion relation and the properties of the most unstable mode are studied in detail and compared with the Maxwellian case. The largest deviations occur at low to intermediate ion-neutral damping. In particular, the growth rate of the instability for ion streaming below the Bohm speed is found to be lower than in the case of Maxwellian ions, yet remains on a significant level even for fast ion flows above the Bohm speed.

The collective motion of dust particles during the mode-coupling–induced melting of a
two-dimensional plasma crystal is explored in molecular-dynamics simulations. The crystal is
compressed horizontally by an anisotropic confinement. This compression leads to an asymmetric
triggering of the mode-coupling instability which is accompanied by alternating chains of in-phase
and anti-phase oscillating particles. A new order parameter is proposed to quantify the
synchronization with respect to different directions of the crystal. Depending on the orientation of
the confinement anisotropy, mode-coupling instability and synchronized motion are observed in one or
two directions. Notably, the synchronization is found to be direction dependent. The good agreement
with experiments suggests that the confinement anisotropy can be used to explain the observed
synchronization process.

The quantum ion-acoustic (QIA) solitary and shock structures formed in a strongly coupled cryogenic
quantum plasma (containing strongly coupled positively charged inertial cold ions and Fermi electrons as well as positrons) have been theoretically investigated. The generalized quantum hydrodynamic model and the reductive perturbation method have been employed to derive the Korteweg-de Vries (K-dV) and Burgers equations. The basic features of the QIA solitary and shock structures are identified by analyzing the stationary solitary and shock wave solutions of the K-dV and Burgers equations. It is found that the basic characteristics (e.g., phase speed, amplitude, and width) of the QIA solitary and shock structures are significantly modified by the effects of the Fermi pressures of electrons and positrons, the ratio of Fermi temperature of positrons to that of electrons, the ratio of effective ion temperature to electron Fermi temperature, etc. It is also observed that the effect of strong correlation among extremely cold ions acts as a source of dissipation, and is responsible for the formation of the QIA shock structures. The results of this theoretical investigation should be useful for understanding the nonlinear features of the localized electrostatic disturbances in laboratory electron-positron-ion plasmas (viz., super-intense laser-dense matter experiments).

Author(s): Yonit Hochberg, Eric Kuflik, Hitoshi Murayama, Tomer Volansky, and Jay G. Wacker

A recent proposal is that dark matter could be a thermal relic of 3 → 2 scatterings in a strongly coupled hidden sector. We present explicit classes of strongly coupled gauge theories that admit this behavior. These are QCD-like theories of dynamical chiral symmetry breaking, where the pions play the …

[Phys. Rev. Lett. 115, 021301] Published Fri Jul 10, 2015

A rigorous theoretical investigation has been made on dust-acoustic (DA) shock structures in an unmagnetized dusty plasma system whose constituents are negatively charged cold mobile dust fluid, electrons following Boltzmann distribution, and positively charged ions of two distinct temperatures following nonextensive ( $q$ ) and nonthermal distributions, respectively. In this paper, the Burgers’ equation has been derived by employing reductive perturbation technique which is valid for small but finite amplitude limit. It is observed that both the nonextensive and nonthermal ions of two distinct temperatures and dust kinematic viscosity significantly modify the basic properties (amplitudes, width, and polarities) of the DA shockwaves (DASHWs). The effects of low (high) temperature ions following nonextensive (nonthermal) and dust kinematic viscosity on DASHWs are examined both analytically and numerically. The implications of these results to some astrophysical environments and space plasmas (e.g., stellar polytropes, peculiar velocity distributions of galaxies, and collisionless thermal plasma), and laboratory dusty plasma systems are briefly mentioned.

Cylindrical and spherical amplitude modulations of dust acoustic (DA) solitary wave envelopes in a strongly coupled dusty plasma containing nonthermal distributed ions are studied. Employing a reductive perturbation technique, a modified nonlinear Schrödinger equation including the geometrical effect is derived. The influences of nonthermal ions, polarization force, and the geometries on the modulational instability conditions are analyzed and the possible rogue wave structures are discussed in detail. It is found that the spherical DA waves are more structurally stable to perturbations than the cylindrical ones. Possible applications of these theoretical findings are briefly discussed.

Thermodynamics of weakly screened (near the one-component-plasma limit)
Yukawa fluids in two and three dimensions is analyzed in detail. It is shown
that the thermal component of the excess internal energy of these fluids, when
expressed in terms of the properly normalized coupling strength, exhibits the
scaling pertinent to the corresponding one-component-plasma limit (the scalings
differ considerably between the two- and three-dimensional situations). This
provides us with a simple and accurate practical tool to estimate thermodynamic
properties of weakly screened Yukawa fluids. Particular attention is paid to
the two-dimensional fluids, for which several important thermodynamic
quantities are calculated to illustrate the application of the approach.

This paper shows that several known properties of the Yukawa system can be
derived from the isomorph theory, which applies to any system that has strong
correlations between its virial and potential-energy equilibrium fluctuations.
Such "Roskilde-simple" systems have a simplified thermodynamic phase diagram
deriving from the fact that they have curves (isomorphs) along which structure
and dynamics in reduced units are invariant to a good approximation. We show
that the Yukawa system has strong virial potential-energy correlations and
identify its isomorphs by two different methods. One method, the so-called
direct isomorph check, identifies isomorphs numerically from jumps of
relatively small density changes (here 10%). The second method identifies
isomorphs analytically from the pair potential. The curves obtained by the two
methods are close to each other; these curves are confirmed to be isomorphs by
demonstrating the invariance of the radial distribution function, the static
structure factor, the mean-square displacement as a function of time, and the
incoherent intermediate scattering function. Since the melting line is
predicted to be an isomorph, the theory provides a derivation of a known
approximate analytical expression for this line in the temperature-density
phase diagram. The paper's results give the first demonstration that the
isomorph theory can be applied to systems like dense colloidal suspensions and
strongly coupled dusty plasmas.

Abstract
In this report an investigation of the properties of a dust acoustic (DA) shock wave propagating in an adiabatic dusty plasma, including the effect of the negative-ion-rich non-thermal ions and trapped electrons, is presented. The reductive perturbation method is employed to derive the modified Burgers equation and a new form of the lower-order nonlinear modified Burgers equation for DA shock waves in a homogeneous, unmagnetized and collisionless plasma whose constituents are electrons, singly-charged positive ions, singly-charged negative ions and massive, charged dust particles. The stationary analytical solution of the Burgers equation and the new analytical solution of the lower-order nonlinear modified Burgers equation are numerically analyzed, and the effects of various dusty plasma constituents on the DA shock wave’s propagation are taken into account. Both positive and negative ions in the dusty plasma are observed to play a key role in the formation of both positive, as well as negative, DA shock waves, and the ion concentration can be used to control the transformation from negative to positive potentials of the waves.