New Enhanced Tunneling in Nuclear Processes

The small sub-barrier tunneling probability of nuclear processes can be dramatically enhanced by collision with incident charged particles. Semiclassical methods of theory of complex trajectories have been applied to nuclear tunneling, and conditions for the effects have been obtained. We demonstrate the enhancement of alpha particle decay by incident proton with energy of about 0.25 MeV. We show that the general features of this process are common for other sub-barrier nuclear processes and can be applied to nuclear fission.Comment: RevTex4, 2 figure

Two-dimensional tunneling in a SQUID

Traditionally quantum tunneling in a static SQUID is studied on the basis of a classical trajectory in imaginary time under a two-dimensional potential barrier. The trajectory connects a potential well and an outer region crossing their borders in perpendicular directions. In contrast to that main-path mechanism, a wide set of trajectories with components tangent to the border of the well can constitute an alternative mechanism of multi-path tunneling. The phenomenon is essentially non-one-dimensional. Continuously distributed paths under the barrier result in enhancement of tunneling probability. A type of tunneling mechanism (main-path or multi-path) depends on character of a state in the potential well prior to tunneling.Comment: 9 pages, 8 figure

Vortex liquid crystals in anisotropic type II superconductors

In a type II superconductor in a moderate magnetic field, the superconductor to normal state transition may be described as a phase transition in which the vortex lattice melts into a liquid. In a biaxial superconductor, or even a uniaxial superconductor with magnetic field oriented perpendicular to the symmetry axis, the vortices acquire elongated cross sections and interactions. Systems of anisotropic, interacting constituents generally exhibit liquid crystalline phases. We examine the possibility of a two step melting in homogeneous type II superconductors with anisotropic superfluid stiffness from a vortex lattice into first a vortex smectic and then a vortex nematic at high temperature and magnetic field. We find that fluctuations of the ordered phase favor an instability to an intermediate smectic-A in the absence of intrinsic pinning

Onset of cavity deformation upon subsonic motion of a projectile in a fluid complex plasma

We study deformation of a cavity around a large projectile moving with subsonic velocity in the cloud of small dust particles. To solve this problem, we employ the Navier--Stokes equation for a compressible fluid with due regard for friction between dust particles and atoms of neutral gas. The solutions shows that due to friction, the pressure of dust cloud at the boundary of the cavity behind the projectile can become negative, which entails formation of a microscopic void free from dust particles -- the cavity deformation. Corresponding threshold velocity is calculated, which is found to decrease with increasing cavity size. Measurement of such velocity makes it possible to estimate the static pressure inside the dust cloud.Comment: 7 pages, 3 figure

Gamma-Ray Emission from Molecular Clouds Generated by Penetrating Cosmic Rays

We analyze the processes governing cosmic-ray (CR) penetration into molecular clouds and the resulting generation of gamma-ray emission. The density of CRs inside a cloud is depleted at lower energies due to the self-excited MHD turbulence. The depletion depends on the effective gas column density ("size") of the cloud. We consider two different environments where the depletion effect is expected to be observed. For the Central Molecular Zone, the expected range of CR energy depletion is $E\lesssim 10$ GeV, leading to the depletion of gamma-ray flux below $E_\gamma\approx 2$ GeV. This effect can be important for the interpretation of the GeV gamma-ray excess in the Galactic Center, which has been revealed from the standard model of CR propagation (assuming the CR spectrum inside a cloud to be equal to the interstellar spectrum). Furthermore, recent observations of some local molecular clouds suggest the depletion of the gamma-ray emission, indicating possible self-modulation of the penetrating low-energy CRs.Comment: 10 pages, 5 figures, accepted for publication in Ap

Negative magnetoresistance and phase slip process in superconducting nanowires

We argue that the negative magnetoresistance of superconducting nanowires, which was observed in recent experiments, can be explained by the influence of the external magnetic field on the critical current of the phase slip process. We show that the suppression of the order parameter in the bulk superconductors made by an external magnetic field can lead to an enhancement of both the first $I_{c1}$ and the second $I_{c2}$ critical currents of the phase slip process in nanowires. Another mechanism of an enhancement of $I_{c1}$ can come from decreasing the decay length of the charge imbalance $\lambda_Q$ at weak magnetic fields because $I_{c1}$ is inversely proportional to $\lambda_Q$. The enhancement of the first critical current leads to a larger intrinsic dissipation of the phase slip process. It suppresses the rate of both the thermo-activated and/or quantum fluctuated phase slips and results in decreasing the fluctuated resistance.Comment: 7 pages, 4 figure

Dynamics of the superconducting condensate in the presence of a magnetic field. Channelling of vortices in superconducting strips at high currents

On the basis of the time-dependent Ginzburg-Landau equation we studied the dynamics of the superconducting condensate in a wide two-dimensional sample in the presence of a perpendicular magnetic field and applied current. We could identify two critical currents: the current at which the pure superconducting state becomes unstable ($J_{c2}$ \cite{self1}) and the current at which the system transits from the resistive state to the superconducting state ($J_{c1}<J_{c2}$). The current $J_{c2}$ decreases monotonically with external magnetic field, while $J_{c1}$ exhibits a maximum at $H^*$. For sufficient large magnetic fields the hysteresis disappears and $J_{c1}=J_{c2}=J_c$. In this high magnetic field region and for currents close to $J_c$ the voltage appears as a result of the motion of separate vortices. With increasing current the moving vortices form 'channels' with suppressed order parameter along which the vortices can move very fast. This leads to a sharp increase of the voltage. These 'channels' resemble in some respect the phase slip lines which occur at zero magnetic field.Comment: 5 pages, 4 figures, Proceedings of Third European Conference on Vortex Matter in Superconductor

Practical dispersion relations for strongly coupled plasma fluids

Very simple explicit analytical expressions are discussed, which are able to describe the dispersion relations of longitudinal waves in strongly coupled plasma systems such as one-component plasma and weakly screened Yukawa fluids with a very good accuracy. Applications to other systems with soft pairwise interactions are briefly discussed.Comment: 11 pages, 3 figures; Related to arXiv:1711.0615

Current-voltage characteristic of narrow superconducting wires: bifurcation phenomena

The current-voltage characteristics of long and narrow superconducting channels are investigated using the time-dependent Ginzburg-Landau equations for complex order parameter. We found out that the steps in the current voltage characteristic can be associated with bifurcations of either steady or oscillatory solution. We revealed typical instabilities which induced the singularities in current-voltage characteristics, and analytically estimated period of oscillations and average voltage in the vicinity of the critical currents. Our results show that these bifurcations can substantially complicate dynamics of the order parameter and eventually lead to appearance of such phenomena as multistability and chaos. The discussed bifurcation phenomena sheds a light on some recent experimental findings

Secondary cosmic-ray nuclei in the model of Galactic halo with nonlinear Landau damping

We employ our recent model of the cosmic-ray (CR) halo by Chernyshov et al. (2022) to compute the Galactic spectra of stable and unstable secondary nuclei. In this model, confinement of the Galactic CRs is entirely determined by the self-generated Alfvenic turbulence whose spectrum is controlled by nonlinear Landau damping. We analyze the physical parameters affecting propagation characteristics of CRs, and estimate the best set of free parameters providing accurate description of available observational data. We also show that agreement with observations at lower energies may be further improved by taking into account the effect of ion-neutral damping which operates near the Galactic disk.Comment: 8 pages, 2 figures. Accepted to Ap