6,731 research outputs found
Bright solitons in Bose-Fermi mixtures
We consider the formation of bright solitons in a mixture of Bose and Fermi
degenerate gases confined in a three-dimensional elongated harmonic trap. The
Bose and Fermi atoms are assumed to effectively attract each other whereas
bosonic atoms repel each other. Strong enough attraction between bosonic and
fermionic components can change the character of the interaction within the
bosonic cloud from repulsive to attractive making thus possible the generation
of bright solitons in the mixture. On the other hand, such structures might be
in danger due to the collapse phenomenon existing in attractive gases. We show,
however, that under some conditions (defined by the strength of the Bose-Fermi
components attraction) the structures which neither spread nor collapse can be
generated. For elongated enough traps the formation of solitons is possible
even at the ``natural'' value of the mutual Bose-Fermi (Rb -K in
our case) scattering length.Comment: 6 pages, 6 figures, 1 tabl
Symmetry Induced 4-Wave Capillary Wave Turbulence
We report theoretical and experimental results on 4-wave capillary wave
turbulence. A system consisting of two inmiscible and incompressible fluids of
the same density can be written in a Hamiltonian way for the conjugated pair
. When given the symmetry , the set of weakly non-linear
interacting waves display a Kolmogorov-Zakharov (KZ) spectrum
in wave vector space. The wave system was studied experimentally with two
inmiscible fluids of almost equal densities (water and silicon oil) where the
capillary surface waves are excited by a low frequency random forcing. The
power spectral density (PSD) and probability density function (PDF) of the
local wave amplitude are studied. Both theoretical and experimental results are
in fairly good agreement with each other.Comment: 6 pages, 2 figure
Coexistence of Weak and Strong Wave Turbulence in a Swell Propagation
By performing two parallel numerical experiments -- solving the dynamical
Hamiltonian equations and solving the Hasselmann kinetic equation -- we
examined the applicability of the theory of weak turbulence to the description
of the time evolution of an ensemble of free surface waves (a swell) on deep
water. We observed qualitative coincidence of the results.
To achieve quantitative coincidence, we augmented the kinetic equation by an
empirical dissipation term modelling the strongly nonlinear process of
white-capping. Fitting the two experiments, we determined the dissipation
function due to wave breaking and found that it depends very sharply on the
parameter of nonlinearity (the surface steepness). The onset of white-capping
can be compared to a second-order phase transition. This result corroborates
with experimental observations by Banner, Babanin, Young.Comment: 5 pages, 5 figures, Submitted in Phys. Rev. Letter
On the infrared limit of Horava's gravity with the global Hamiltonian constraint
We show that Horava's theory of gravitation with the global Hamiltonian
constraint does not reproduce General Relativity in the infrared domain. There
is one extra propagating degree of freedom, besides those two associated with
the massless graviton, which does not decouple.Comment: 7 pages, typos corrected, to be published in PR
Quantum Many-Body Dynamics of Dark Solitons in Optical Lattices
We present a fully quantum many-body treatment of dark solitons formed by
ultracold bosonic atoms in one-dimensional optical lattices. Using
time-evolving block decimation to simulate the single-band Bose-Hubbard
Hamiltonian, we consider the quantum dynamics of density and phase engineered
dark solitons as well as the quantum evolution of mean-field dark solitons
injected into the quantum model. The former approach directly models how one
may create quantum entangled dark solitons in experiment. While we have already
presented results regarding the latter approach elsewhere [Phys. Rev. Lett.
{\bf 103}, 140403 (2009)], we expand upon those results in this work. In both
cases, quantum fluctuations cause the dark soliton to fill in and may induce an
inelasticity in soliton-soliton collisions. Comparisons are made to the
Bogoliubov theory which predicts depletion into an anomalous mode that fills in
the soliton. Our many-body treatment allows us to go beyond the Bogoliubov
approximation and calculate explicitly the dynamics of the system's natural
orbitals.Comment: 14 pages, 11 figures -- v3 has only minor changes from v2 -- this is
the print versio
New multidimensional partially integrable generalization of S-integrable N-wave equation
This paper develops a modification of the dressing method based on the
inhomogeneous linear integral equation with integral operator having nonempty
kernel. Method allows one to construct the systems of multidimensional Partial
Differential Equations (PDEs) having the differential polynomial forms in any
dimension n. Associated solution space is not full, although it is parametrized
by a certain number of arbitrary functions of (n-1)-variables. We consider
4-dimensional generalization of the classical (2+1)-dimensional S-integrable
N-wave equation as an example.Comment: 38 page
Two-dimensional ring-like vortex and multisoliton nonlinear structures at the upper-hybrid resonance
Two-dimensional (2D) equations describing the nonlinear interaction between
upper-hybrid and dispersive magnetosonic waves are presented. Nonlocal
nonlinearity in the equations results in the possibility of existence of stable
2D nonlinear structures. A rigorous proof of the absence of collapse in the
model is given. We have found numerically different types of nonlinear
localized structures such as fundamental solitons, radially symmetric vortices,
nonrotating multisolitons (two-hump solitons, dipoles and quadrupoles), and
rotating multisolitons (azimuthons). By direct numerical simulations we show
that 2D fundamental solitons with negative hamiltonian are stable.Comment: 8 pages, 6 figures, submitted to Phys. Plasma
Self-accelerating solutions in massive gravity on an isotropic reference metric
Within the framework of the recently proposed ghost-free massive gravity, a
cosmological constant-type self-accelerating solution has been obtained for
Minkowski and de Sitter reference metrics. We ease the assumption on the
reference metric and find the self-accelerating solution for the reference
metric respecting only isotropy, thus considerably extending the range of known
solutions.Comment: 4 pages; matches the published version in Phys. Rev.
Nonperturbative physics at short distances
There is accumulating evidence in lattice QCD that attempts to locate
confining fields in vacuum configurations bring results explicitly depending on
tha lattice spacing (that is, ultraviolet cut off). Generically, one deals with
low-dimensional vacuum defects which occupy a vanishing fraction of the total
four-dimensional space. We review briefly existing data on the vacuum defects
and their significance for confinement and other nonperturbative phenomena. We
introduce the notion of `quantum numbers' of the defects and draw an analogy,
rather formal one, to developments which took place about 50 years ago and were
triggered by creation of the Sakata model.Comment: 15 pages, contributed to International Symposium on the Jubilee of
the Sakata Model (pnLambda50), Nagoya, Japan, Nov. 200
- …