52 research outputs found
Barotropic thin shells with linear EOS as models of stars and circumstellar shells in general relativity
The spherically symmetric thin shells of the barotropic fluids with the
linear equation of state are considered within the frameworks of general
relativity. We study several aspects of the shells as completely relativistic
models of stars, first of all the neutron stars and white dwarfs, and
circumstellar shells. The exact equations of motion of the shells are obtained.
Also we calculate the parameters of the equilibrium configurations, including
the radii of static shells. Finally, we study the stability of the equilibrium
shells against radial perturbations.Comment: final version; ps-version of figure is available by email request to
[email protected]
Mass of perfect fluid black shells
The spherically symmetric singular perfect fluid shells are considered for
the case of their radii being equal to the event horizon (the black shells). We
study their observable masses, depending at least on the three parameters,
viz., the square speed of sound in the shell, instantaneous radial velocity of
the shell at a moment when it reaches the horizon, and integration constant
related to surface mass density. We discuss the features of black shells
depending on an equation of state.Comment: 1 figure, LaTeX; final version + FA
Cosmic Strings in the Abelian Higgs Model with Conformal Coupling to Gravity
Cosmic string solutions of the abelian Higgs model with conformal coupling to
gravity are shown to exist. The main characteristics of the solutions are
presented and the differences with respect to the minimally coupled case are
studied. An important difference is the absence of Bogomolnyi cosmic string
solutions for conformal coupling. Several new features of the abelian Higgs
cosmic strings of both types are discussed. The most interesting is perhaps a
relation between the angular deficit and the central magnetic field which is
bounded by a critical value.Comment: 22 pages, 10 figures; to appear in Phys. Rev.
Gauge Invariant Hamiltonian Formalism for Spherically Symmetric Gravitating Shells
The dynamics of a spherically symmetric thin shell with arbitrary rest mass
and surface tension interacting with a central black hole is studied. A careful
investigation of all classical solutions reveals that the value of the radius
of the shell and of the radial velocity as an initial datum does not determine
the motion of the shell; another configuration space must, therefore, be found.
A different problem is that the shell Hamiltonians used in literature are
complicated functions of momenta (non-local) and they are gauge dependent. To
solve these problems, the existence is proved of a gauge invariant
super-Hamiltonian that is quadratic in momenta and that generates the shell
equations of motion. The true Hamiltonians are shown to follow from the
super-Hamiltonian by a reduction procedure including a choice of gauge and
solution of constraint; one important step in the proof is a lemma stating that
the true Hamiltonians are uniquely determined (up to a canonical
transformation) by the equations of motion of the shell, the value of the total
energy of the system, and the choice of time coordinate along the shell. As an
example, the Kraus-Wilczek Hamiltonian is rederived from the super-Hamiltonian.
The super-Hamiltonian coincides with that of a fictitious particle moving in a
fixed two-dimensional Kruskal spacetime under the influence of two effective
potentials. The pair consisting of a point of this spacetime and a unit
timelike vector at the point, considered as an initial datum, determines a
unique motion of the shell.Comment: Some remarks on the singularity of the vector potantial are added and
some minor corrections done. Definitive version accepted in Phys. Re
Complete Classification of the String-like Solutions of the Gravitating Abelian Higgs Model
The static cylindrically symmetric solutions of the gravitating Abelian Higgs
model form a two parameter family. In this paper we give a complete
classification of the string-like solutions of this system. We show that the
parameter plane is composed of two different regions with the following
characteristics: One region contains the standard asymptotically conic cosmic
string solutions together with a second kind of solutions with Melvin-like
asymptotic behavior. The other region contains two types of solutions with
bounded radial extension. The border between the two regions is the curve of
maximal angular deficit of .Comment: 12 pages, 4 figure
A Wormhole at the core of an infinite cosmic string
We study a solution of Einstein's equations that describes a straight cosmic
string with a variable angular deficit, starting with a deficit at the
core. We show that the coordinate singularity associated to this defect can be
interpreted as a traversible wormhole lodging at the the core of the string. A
negative energy density gradually decreases the angular deficit as the distance
from the core increases, ending, at radial infinity, in a Minkowski spacetime.
The negative energy density can be confined to a small transversal section of
the string by gluing to it an exterior Gott's like solution, that freezes the
angular deficit existing at the matching border. The equation of state of the
string is such that any massive particle may stay at rest anywhere in this
spacetime. In this sense this is 2+1 spacetime solution.Comment: 1 tex file and 5 eps files. To be Published in Nov. in Phys.Rev.
Electroweak String Configurations with Baryon Number
In the context of electroweak strings, the baryon number anomaly equation may
be reinterpreted as a conservation law for baryon number minus helicity. Since
the helicity is a sum of the link and twist numbers, linked or twisted loops of
electroweak string carry baryon number. We evaluate the change in the baryon
number obtained by delinking loops of electroweak string and show that
twisted electroweak string segments may be regarded as extended sphalerons. We
also suggest an alternative scenario for electroweak baryogenesis.Comment: 11 pages, figure available on request. Added discussion of
string-sphaleron connection for non-vanishing Weinberg angle and shortened
discussion on formation of linked configuration
Euclidean Black Hole Vortices
We argue the existence of solutions of the Euclidean Einstein equations that
correspond to a vortex sitting at the horizon of a black hole. We find the
asymptotic behaviours, at the horizon and at infinity, of vortex solutions for
the gauge and scalar fields in an abelian Higgs model on a Euclidean
Schwarzschild background and interpolate between them by integrating the
equations numerically. Calculating the backreaction shows that the effect of
the vortex is to cut a slice out of the Euclidean Schwarzschild geometry.
Consequences of these solutions for black hole thermodynamics are discussed.Comment: 24 page
Photometric redshifts for supernovae Ia in the Supernova Legacy Survey
We present a method using the SALT2 light curve fitter to determine the
redshift of Type Ia supernovae in the Supernova Legacy Survey (SNLS) based on
their photometry in g', r', i' and z'. On 289 supernovae of the first three
years of SNLS data, we obtain a precision on
average up to a redshift of 1.0, with a higher precision of 0.016 for z<0.45
and a lower one of 0.025 for z>0.45. The rate of events with (catastrophic errors) is 1.4%. Both the precision and the rate
of catastrophic errors are better than what can be currently obtained using
host galaxy photometric redshifts. Photometric redshifts of this precision may
be useful for future experiments which aim to discover up to millions of
supernovae Ia but without spectroscopy for most of them.Comment: 7 pages, 9 figures, published in Astronomy and Astrophysic
Topological Defects as Seeds for Eternal Inflation
We investigate the global structure of inflationary universe both by
analytical methods and by computer simulations of stochastic processes in the
early Universe. We show that the global structure of the universe depends
crucially on the mechanism of inflation. In the simplest models of chaotic
inflation the Universe looks like a sea of thermalized phase surrounding
permanently self-reproducing inflationary domains. In the theories where
inflation occurs near a local extremum of the effective potential corresponding
to a metastable state, the Universe looks like de Sitter space surrounding
islands of thermalized phase. A similar picture appears even if the state is unstable but the effective potential has a discrete symmetry . In this case the Universe becomes divided into domains containing
different phases. These domains will be separated from each other by domain
walls. However, unlike ordinary domain walls, these domain walls will inflate,
and their thickness will exponentially grow. In the theories with continuous
symmetries inflation generates exponentially expanding strings and monopoles
surrounded by thermalized phase. Inflating topological defects will be stable,
and they will unceasingly produce new inflating topological defects. This means
that topological defects may play a role of indestructible seeds for eternal
inflation.Comment: 21 pages, 17 figures (not included), Stanford University preprint
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