2,127 research outputs found
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
eV suppressed by the Planckian mass
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 . 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
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