2,129 research outputs found
Scalar multi-wormholes
In 1921 Bach and Weyl derived the method of superposition to construct new
axially symmetric vacuum solutions of General Relativity. In this paper we
extend the Bach-Weyl approach to non-vacuum configurations with massless scalar
fields. Considering a phantom scalar field with the negative kinetic energy, we
construct a multi-wormhole solution describing an axially symmetric
superposition of wormholes. The solution found is static, everywhere
regular and has no event horizons. These features drastically tell the
multi-wormhole configuration from other axially symmetric vacuum solutions
which inevitably contain gravitationally inert singular structures, such as
`struts' and `membranes', that keep the two bodies apart making a stable
configuration. However, the multi-wormholes are static without any singular
struts. Instead, the stationarity of the multi-wormhole configuration is
provided by the phantom scalar field with the negative kinetic energy. Anther
unusual property is that the multi-wormhole spacetime has a complicated
topological structure. Namely, in the spacetime there exist
asymptotically flat regions connected by throats.Comment: 11 pages, 13 figure
Precision measurements of s-wave scattering lengths in a two-component Bose-Einstein condensate
We use collective oscillations of a two-component Bose-Einstein condensate
(2CBEC) of \Rb atoms prepared in the internal states and for the precision measurement of
the interspecies scattering length with a relative uncertainty of
. We show that in a cigar-shaped trap the three-dimensional
(3D) dynamics of a component with a small relative population can be
conveniently described by a one-dimensional (1D) Schr\"{o}dinger equation for
an effective harmonic oscillator. The frequency of the collective oscillations
is defined by the axial trap frequency and the ratio , where
is the intra-species scattering length of a highly populated component
1, and is largely decoupled from the scattering length , the total atom
number and loss terms. By fitting numerical simulations of the coupled
Gross-Pitaevskii equations to the recorded temporal evolution of the axial
width we obtain the value , where is the Bohr
radius. Our reported value is in a reasonable agreement with the theoretical
prediction but deviates significantly from the
previously measured value \cite{Mertes07} which is commonly
used in the characterisation of spin dynamics in degenerate \Rb atoms. Using
Ramsey interferometry of the 2CBEC we measure the scattering length
which also deviates from the previously reported value
\cite{Mertes07}. We characterise two-body losses for the
component 2 and obtain the loss coefficients
and
.Comment: 11 pages, 8 figure
Strong light-matter coupling: parametric interactions in a cavity and free-space
We consider parametric interactions of laser pulses in a coherent macroscopic
ensemble of resonant atoms, which are possible in the strong coupling regime of
light-matter interaction. The spectrum condensation (lasing at collective
vacuum Rabi sidebands) was studied in an active cavity configuration.
Parametric interactions under the strong light-matter coupling were proved even
in free space. In contrast to bichromatic beats in a cavity, they were shown to
appear due to interference between polaritonic wave packets of different group
velocities.Comment: 4 pages, 2 figure
Inadequate fat diet
Aim. To determine the main factors of inadequate fat diet (IAFD) and indicate the ways of their change.Methods. Analysis and generalization of existing scientific literature data and the results of our own research.Results. The following factors of IAFD have been identified:1) excess fat in the diet;2) an excess of palmitic acid in dietary fats;3) an excess of linoleic acid in dietary fats;4) consumption of thermoperoxide fats;5) deficiency of ω-3 polyunsaturated fatty acids (PUFA).Conclusion. IAFD is a cause of metabolic and neuropsychiatric disorders underlying non-communicable diseases
Mean-field dynamics of two-mode Bose-Einstein condensates in highly anisotropic potentials: Interference, dimensionality, and entanglement
We study the mean-field dynamics and the reduced-dimension character of
two-mode Bose-Einstein condensates (BECs) in highly anisotropic traps. By means
of perturbative techniques, we show that the tightly confined (transverse)
degrees of freedom can be decoupled from the dynamical equations at the expense
of introducing additional effective three-body, attractive, intra- and
inter-mode interactions into the dynamics of the loosely confined
(longitudinal) degrees of freedom. These effective interactions are mediated by
changes in the transverse wave function. The perturbation theory is valid as
long as the nonlinear scattering energy is small compared to the transverse
energy scales. This approach leads to reduced-dimension mean-field equations
that optimally describe the evolution of a two-mode condensate in general
quasi-1D and quasi-2D geometries. We use this model to investigate the relative
phase and density dynamics of a two-mode, cigar-shaped Rb BEC. We study
the relative-phase dynamics in the context of a nonlinear Ramsey interferometry
scheme, which has recently been proposed as a novel platform for high-precision
interferometry. Numerical integration of the coupled, time-dependent,
three-dimensional, two-mode Gross-Pitaevskii equations for various atom numbers
shows that this model gives a considerably more refined analytical account of
the mean-field evolution than an idealized quasi-1D description.Comment: 35 pages, 10 figures. Current version is as publishe
Heat-kernel coefficients for oblique boundary conditions
We calculate the heat-kernel coefficients, up to , for a U(1) bundle on
the 4-Ball for boundary conditions which are such that the normal derivative of
the field at the boundary is related to a first-order operator in boundary
derivatives acting on the field. The results are used to place restrictions on
the general forms of the coefficients. In the specific case considered, there
can be a breakdown of ellipticity.Comment: 9 pages, JyTeX. One reference added and minor corrections mad
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