Modulational instability of a Langmuir wave in plasmas with energetic tails of superthermal electrons

The impact of superthermal electrons on dispersion properties of isotropic plasmas and on the modulational instability of a monochromatic Langmuir wave is studied for the case when the power-law tail of the electron distribution function extends to relativistic velocities and contains most of the plasma kinetic energy. Such an energetic tail of electrons is shown to increase the thermal correction to the Langmuir wave frequency, which is equivalent to the increase of the effective electron temperature in the fluid approach, and has almost no impact on the dispersion of ion-acoustic waves, in which the role of temperature is played by the thermal spread of low-energy core electrons. It is also found that the spectrum of modulational instability in the non-maxwellian plasma narrows significantly, as compared to the equilibrium case, without change of the maximum growth rate and the corresponding wavenumber

Two-dimensional simulations of nonlinear beam-plasma interaction in isotropic and magnetized plasmas

Nonlinear interaction of a low density electron beam with a uniform plasma is studied using two-dimensional particle-in-cell (PIC) simulations. We focus on formation of coherent phase space structures in the case, when a wide two-dimensional wave spectrum is driven unstable, and we also study how nonlinear evolution of these structures is affected by the external magnetic field. In the case of isotropic plasma, nonlinear buildup of filamentation modes due to the combined effects of two-stream and oblique instabilities is found to exist and growth mechanisms of secondary instabilities destroying the BGK--type nonlinear wave are identified. In the weak magnetic field, the energy of beam-excited plasma waves at the nonlinear stage of beam-plasma interaction goes predominantly to the short-wavelength upper-hybrid waves propagating parallel to the magnetic field, whereas in the strong magnetic field the spectral energy is transferred to the electrostatic whistlers with oblique propagation

The surface density of holographic entropy

On the basis of postulates for the holographic description of gravity and the introduction of entropic force, for static sources we derive the universal law: the entropy of a holographic screen is equal to quarter of its area in the Planck system of units.Comment: 6 page

Natural scale of cosmological constant in seesaw mechanism with broken SUSY

The cosmological constant is inherently determined by the scale of breaking down supersymmetry in the mechanism of seesaw fluctuations of two vacuum-states.Comment: 4 pages, revtex4 class, reference adde

Properties of potential modelling three benchmarks: the cosmological constant, inflation and three generations

We argue for a model of low-energy correction to the inflationary potential as caused by the gauge-mediated breaking down the supersymmetry at the scale of \mu_\textsc{x}\sim 10^4 GeV, that provides us with the seesaw mechanism of thin domain wall fluctuations in the flat vacuum. The fluctuations are responsible for the vacuum with the cosmological constant at the scale of $\mu_\Lambda\sim 10^{-2}$ eV suppressed by the Planckian mass $m_\mathtt{Pl}$ via \mu_\Lambda\sim\mu_\textsc{x}^2/m_\mathtt{Pl}. The appropriate vacuum state is occupied after the inflation with quartic coupling constant \lambda\sim\mu_\textsc{x}/m_\mathtt{Pl}\sim 10^{-14} inherently related with the bare mass scale of \widetilde m\sim\sqrt{\mu_\textsc{x}m_\mathtt{Pl}}\sim 10^{12} GeV determining the thickness of domain walls $\delta r\sim1/\widetilde m$. Such the parameters of potential are still marginally consistent with the observed inhomogeneity of matter density in the Universe. The inflationary evolution suggests the vacuum structure compatible with three fermionic generations of matter as well as with observed hierarchies of masses and mixing in the Standard Model.Comment: 12 pages, 1 figure, revtex4 class, references adde

Renormalization group analysis of cosmological constraint on the mass of Higgs scalar

The Higgs boson of Standard Model, minimally coupled to the gravitation, is not able to produce the inflation of early Universe if its mass exceeds the threshold value, which is equal to m_H^{min} = 142 GeV in the tree approximation for the scalar potential. Two-loop corrections modify the estimate as m_H^{min} = 150 \pm 3 GeV, so that higher-order corrections of perturbation theory are completely under control, though they are numerically important in respect of experimental searches.Comment: 6 page

Possible Josephson-like behavior of the YBa2Cu3O7-x single crystal twin boundaries in low magnetic fields

The experimental results on the magnetic response of YBCO single crystals with unidirectional twin boundary planes in low magnetic fields (0.01 - 1 Oe) are discussed. The observed non-monotone temperature dependence of magnetization is interpreted within a plausible model of a system of the Josephson weak links in the twin boundary planes and on the basis of the order parameter anisotropy.Comment: 4 pages, 2 figures, the full version will be published in Low Temperature Physics (2004

Compensation of Dipolar-Exciton Spin Splitting in Magnetic Field

Magnetoluminescence of spatially indirect dipolar excitons collected in 25 nm GaAs/AlGaAs single quantum well within a lateral potential trap has been studied in perpendicular magnetic field in Faraday geometry. The paramagnetic spin splitting of the luminescence line of the heavy-hole excitons in the trap centre is completely compensated at magnetic fields below critical value, around 2 Tesla. The effect of spin-splitting compensation is caused by the exchange interaction in dense exciton Bose gas which is in qualitative agreement with the existing theoretical concepts. In the range of low magnetic fields, less than 1.5 Tesla, an unusually large blue shift, upto 3 meV, is observed, which is related to in-plane electric field component present in nonhomogeneous electrostatic field of the trap.Comment: 9 pages, 3 figure

Temporal shape manipulation of adiabatons

We describe how to control the temporal shape of adiabaton using peculiarities of propagation dynamics under coherent population trapping. Temporal compression is demonstrated as a special case of pulse shaping. The general case of unequal oscillator strengths of two optical transitions in atom is considered.Comment: 5 pages, 7 figures, LaTeX, sent to Phys. Rev. A, correct indices added in fig

The holographic screen at low temperatures

A permissible spectrum of transverse vibrations for the holographic screen modifies both a distribution of thermal energy over bits at low temperatures and the law of gravitation at small accelerations of free fall in agreement with observations of flat rotation curves in spiral galaxies. This modification relates holographic screen parameters in de Sitter space-time with the Milgrom acceleration in MOND.Comment: 7 pages, 1 figur