31 research outputs found
Time-Lapse Microscopy
Time-lapse microscopy is a powerful, versatile and constantly developing tool for real-time imaging of living cells. This review outlines the advances of time-lapse microscopy and refers to the most interesting reports, thus pointing at the fact that the modern biology and medicine are entering the thrilling and promising age of molecular cinematography
Cosmological thermodynamics and deflationary gas universe
We establish a general thermodynamic scheme for cosmic fluids with internal
self-interactions and discuss equilibrium and non-equilibrium aspects of such
systems in connection with (generalized) symmetry properties of the
cosmological dynamics. As an example we construct an exactly solvable gas
dynamical model of a ``deflationary'' transition from an initial de Sitter
phase to a subsequent Friedmann-Lema\^{\i}tre-Robertson-Walker (FLRW) period.
We demonstrate that this dynamics represents a manifestation of a conformal
symmetry of an ``optical'' metric, characterized by a specific effective
refraction index of the cosmic medium.Comment: 12 pages, to appear in PR
Stochastic Production Of Kink-Antikink Pairs In The Presence Of An Oscillating Background
We numerically investigate the production of kink-antikink pairs in a
dimensional field theory subject to white noise and periodic driving.
The twin effects of noise and periodic driving acting in conjunction lead to
considerable enhancement in the kink density compared to the thermal
equilibrium value, for low dissipation coefficients and for a specific range of
frequencies of the oscillating background. The dependence of the kink-density
on the temperature of the heat bath, the amplitude of the oscillating
background and value of the dissipation coefficient is also investigated. An
interesting feature of our result is that kink-antikink production occurs even
though the system always remains in the broken symmetry phase.Comment: Revtex, 21 pages including 7 figures; more references adde
Cosmic Strings and the String Dilaton
The existence of a dilaton (or moduli) with gravitational-strength coupling
to matter imposes stringent constraints on the allowed energy scale of cosmic
strings, . In particular, superheavy gauge strings with are ruled out unless the dilaton mass m_{\phi} \gsim 100 TeV,
while the currently popular value imposes the bound \eta
\lsim 3 \times 10^{11} GeV. Similar constraints are obtained for global
topological defects. Some non-standard cosmological scenarios which can avoid
these constraints are pointed out.Comment: 16 page
Aspects of Tachyonic Inflation with Exponential Potential
We consider issues related to tachyonic inflation with exponential potential.
We find exact solution of evolution equations in the slow roll limit in FRW
cosmology. We also carry out similar analysis in case of Brane assisted
tachyonic inflation. We investigate the phase space behavior of the system and
show that the dust like solution is a late time attractor. The difficulties
associated with reheating in the tachyonic model are also indicated.Comment: New References added. To appear in Phys. Rev.
Anisotropic Inflation and the Origin of Four Large Dimensions
In the context of (4+d)-dimensional general relativity, we propose an
inflationary scenario wherein 3 spatial dimensions grow large, while d extra
dimensions remain small. Our model requires that a self-interacting d-form
acquire a vacuum expectation value along the extra dimensions. This causes 3
spatial dimensions to inflate, whilst keeping the size of the extra dimensions
nearly constant. We do not require an additional stabilization mechanism for
the radion, as stable solutions exist for flat, and for negatively curved
compact extra dimensions. From a four-dimensional perspective, the radion does
not couple to the inflaton; and, the small amplitude of the CMB temperature
anisotropies arises from an exponential suppression of fluctuations, due to the
higher-dimensional origin of the inflaton. The mechanism triggering the end of
inflation is responsible, both, for heating the universe, and for avoiding
violations of the equivalence principle due to coupling between the radion and
matter.Comment: 24 pages, 2 figures; uses RevTeX4. v2: Minor changes and added
references. v3: Improved discussion of slow-rol
Topological defects and open inflation
Topological defects can naturally be formed soon after bubble nucleation in
the open inflation scenario. The defects are not completely diluted away by the
subsequent period of inflation in the bubble interior and can produce
observable large-scale microwave background anisotropies. Superheavy strings
and monopoles attached to the strings can act as gravitational lenses with
angular separation between the images of up to an arc minute.Comment: 11 pages, revte
Possible Origin of Antimatter Regions in the Baryon Dominated Universe
We discuss the evolution of U(1) symmetric scalar field at the inflation
epoch with a pseudo Nambu-Goldstone tilt revealing after the end of exponential
expansion of the Universe. The U(1) symmetry is supposed to be associated with
baryon charge. It is shown that quantum fluctuations lead in natural way to
baryon dominated Universe with antibaryon excess regions. The range of
parameters is calculated at which the fraction of Universe occupied by
antimatter and the size of antimatter regions satisfy the observational
constraints, survive to the modern time and lead to effects, accessible to
experimental search for antimatter.Comment: 10 pages, 1 figur
AdS and stabilized extra dimensions in multidimensional gravitational models with nonlinear scalar curvature terms 1/R and R^4
We study multidimensional gravitational models with scalar curvature
nonlinearities of the type 1/R and R^4. It is assumed that the corresponding
higher dimensional spacetime manifolds undergo a spontaneous compactification
to manifolds with warped product structure. Special attention is paid to the
stability of the extra-dimensional factor spaces. It is shown that for certain
parameter regions the systems allow for a freezing stabilization of these
spaces. In particular, we find for the 1/R model that configurations with
stabilized extra dimensions do not provide a late-time acceleration (they are
AdS), whereas the solution branch which allows for accelerated expansion (the
dS branch) is incompatible with stabilized factor spaces. In the case of the
R^4 model, we obtain that the stability region in parameter space depends on
the total dimension D=dim(M) of the higher dimensional spacetime M. For D>8 the
stability region consists of a single (absolutely stable) sector which is
shielded from a conformal singularity (and an antigravity sector beyond it) by
a potential barrier of infinite height and width. This sector is smoothly
connected with the stability region of a curvature-linear model. For D<8 an
additional (metastable) sector exists which is separated from the conformal
singularity by a potential barrier of finite height and width so that systems
in this sector are prone to collapse into the conformal singularity. This
second sector is not smoothly connected with the first (absolutely stable) one.
Several limiting cases and the possibility for inflation are discussed for the
R^4 model.Comment: 28 pages, minor cosmetic improvements, Refs. added; to appear in
Class. Quantum Gra
Non-equilibrium electroweak baryogenesis from preheating after inflation
We present a novel scenario for baryogenesis in a hybrid inflation model at
the electroweak scale, in which the Standard Model Higgs field triggers the end
of inflation. One of the conditions for successful baryogenesis, the departure
from thermal equilibrium, is naturally achieved at the stage of preheating
after inflation. The inflaton oscillations induce large occupation numbers for
long-wavelength configurations of Higgs and gauge fields, which leads to a
large rate of sphaleron transitions. We estimate this rate during the first
stages of reheating and evaluate the amount of baryons produced due to a
particular type of higher dimensional CP violating operator. The universe
thermalizes through fermion interactions, at a temperature below critical,
GeV, preventing the wash-out of the produced baryon asymmetry.
Numerical simulations in (1+1) dimensions support our theoretical analysis.Comment: 11 pages, ReVTeX, 16 figures inserted with epsf. Small changes in the
introduction and new reference