16,034 research outputs found
Evolution of primordial black holes in Jordan-Brans-Dicke cosmology
We consider the evolution of primordial black holes in a generalyzed
Jordan-Brans-Dicke cosmological model where both the Brans-Dicke scalar field
and its coupling to gravity are dynamical functions determined from the
evolution equations. The evaporation rate for the black holes changes compared
to that in standard cosmology. We show that accretion of radiation can proceed
effectively in the radiation dominated era. The black hole lifetime shortens
for low initial mass, but increases for high initial mass, and is thus
considerably modified compared to the case of standard cosmology. We derive a
cut-off value for the initial black hole mass, below which primordial black
holes evaporate out in the radiation dominated era, and above which they
survive beyond the present era.Comment: 5 pages, Latex; uses MNRAS stylefiles; minor changes; accepted for
publication in MNRA
Fractional charge excitations in fermionic ladders
The system of interacting spinless fermions hopping on a two-leg ladder in
the presence of an external magnetic field is shown to possess a long range
order: the bond density wave or the staggered flux phase. In both cases the
elementary excitations are kinks and carry one half the charge of an
electron.Comment: 4 pages, 3 figure
Growth of primordial black holes in a universe containing a massless scalar field
The evolution of primordial black holes in a flat Friedmann universe with a
massless scalar field is investigated in fully general relativistic numerical
relativity. A primordial black hole is expected to form with a scale comparable
to the cosmological apparent horizon, in which case it may go through an
initial phase with significant accretion. However, if it is very close to the
cosmological apparent horizon size, the accretion is suppressed due to general
relativistic effects. In any case, it soon gets smaller than the cosmological
horizon and thereafter it can be approximated as an isolated vacuum solution
with decaying mass accretion. In this situation the dynamical and inhomogeneous
scalar field is typically equivalent to a perfect fluid with a stiff equation
of state . The black hole mass never increases by more than a factor of
two, despite recent claims that primordial black holes might grow substantially
through accreting quintessence. It is found that the gravitational memory
scenario, proposed for primordial black holes in Brans-Dicke and scalar-tensor
theories of gravity, is highly unphysical.Comment: 24 pages, accepted for publication in Physical Review
Holes in the walls: primordial black holes as a solution to the cosmological domain wall problem
We propose a scenario in which the cosmological domain wall and monopole
problems are solved without any fine tuning of the initial conditions or
parameters in the Lagrangian of an underlying filed theory. In this scenario
domain walls sweep out (unwind) the monopoles from the early universe, then the
fast primordial black holes perforate the domain walls, change their topology
and destroy them. We find further that the (old vacuum) energy density released
from the domain walls could alleviate but not solve the cosmological flatness
problem.Comment: References added; Published in Phys. Rev.
Self-similar cosmological solutions with dark energy. II: black holes, naked singularities and wormholes
We use a combination of numerical and analytical methods, exploiting the
equations derived in a preceding paper, to classify all spherically symmetric
self-similar solutions which are asymptotically Friedmann at large distances
and contain a perfect fluid with equation of state with
. The expansion of the Friedmann universe is accelerated in this
case. We find a one-parameter family of self-similar solutions representing a
black hole embedded in a Friedmann background. This suggests that, in contrast
to the positive pressure case, black holes in a universe with dark energy can
grow as fast as the Hubble horizon if they are not too large. There are also
self-similar solutions which contain a central naked singularity with negative
mass and solutions which represent a Friedmann universe connected to either
another Friedmann universe or some other cosmological model. The latter are
interpreted as self-similar cosmological white hole or wormhole solutions. The
throats of these wormholes are defined as two-dimensional spheres with minimal
area on a spacelike hypersurface and they are all non-traversable because of
the absence of a past null infinity.Comment: 12 pages, 19 figures, 1 table, final version to appear in Physical
Review
Near-Critical Gravitational Collapse and the Initial Mass Function of Primordial Black Holes
The recent discovery of critical phenomena arising in gravitational collapse
near the threshold of black hole formation is used to estimate the initial mass
function of primordial black holes (PBHs). It is argued that the universal
scaling relation between black hole mass and initial perturbation found for a
variety of collapsing space-times also applies to PBH formation, indicating the
possibility of the formation of PBHs with masses much smaller than one horizon
mass. Owing to the natural fine-tuning of initial conditions by the exponential
decline of the probability distribution for primordial density fluctuations,
sub-horizon mass PBHs are expected to form at all epochs. This result suggests
that the constraints on the primordial fluctuation spectrum based on the
abundance of PBHs at different mass scales may have to be revisited.Comment: 4 pages, uses revtex, also available at
http://bigwhirl.uchicago.edu/jcn/pub_pbh.html . To appear in Phys. Rev. Let
Stability criterion for self-similar solutions with a scalar field and those with a stiff fluid in general relativity
A stability criterion is derived in general relativity for self-similar
solutions with a scalar field and those with a stiff fluid, which is a perfect
fluid with the equation of state . A wide class of self-similar
solutions turn out to be unstable against kink mode perturbation. According to
the criterion, the Evans-Coleman stiff-fluid solution is unstable and cannot be
a critical solution for the spherical collapse of a stiff fluid if we allow
sufficiently small discontinuity in the density gradient field in the initial
data sets. The self-similar scalar-field solution, which was recently found
numerically by Brady {\it et al.} (2002 {\it Class. Quantum. Grav.} {\bf 19}
6359), is also unstable. Both the flat Friedmann universe with a scalar field
and that with a stiff fluid suffer from kink instability at the particle
horizon scale.Comment: 15 pages, accepted for publication in Classical and Quantum Gravity,
typos correcte
Asymptotically Friedmann self-similar scalar field solutions with potential
We investigate self-similar solutions which are asymptotic to the Friedmann
universe at spatial infinity and contain a scalar field with potential. The
potential is required to be exponential by self-similarity. It is found that
there are two distinct one-parameter families of asymptotic solutions,one is
asymptotic to the proper Friedmann universe, while the other is asymptotic to
the quasi-Friedmann universe, i.e., the Friedmann universe with anomalous solid
angle. The asymptotically proper Friedmann solution is possible only if the
universe is accelerated or the potential is negative. If the potential is
positive, the density perturbation in the asymptotically proper Friedmann
solution rapidly falls off at spatial infinity, while the mass perturbation is
compensated. In the asymptotically quasi-Friedmann solution, the density
perturbation falls off only in proportion to the inverse square of the areal
radius and the relative mass perturbation approaches a nonzero constant at
spatial infinity. The present result shows that a necessary condition holds in
order that a self-gravitating body grows self-similarly due to the constant
accretion of quintessence in an accelerating universe.Comment: accepted for publication in Physical Review D, minor correction,
typos correcte
Abnormal prothrombin (DES-y-Carboxy Prothrombin) in hepatocellular carcinoma
Des-γ-carboxy prothrombin (DCP), a protein induced by vitamin K absence or antagonist-II (PIVKA-II) was measured by an enzyme immunoassay (E-1023) using anti-DCP monoclonal antibody in 92 patients with various hepatobiliary diseases. Thirty-six of the 38 patients (94.7%) with hepatocellular carcinoma (HCC) had abnormal DCP levels greater than 0.1 arbitrary unit (AU)/ml, but only 18 of the 35 patients (51.4%) had AFP greater than 100 ng/ml (suspicious levels for HCC). There was no correlation between plasma or serum DCP and serum alpha-fetoprotein (AFP) levels. Serum alpha fetoprotein was elevated (above 20 ng/ml) in 23 of the 35 patients (65.7%), and DCP was elevated in all of the remaining 12 patients with normal AFP. DCP levels returned to normal levels following curative hepatic resection or orthotopic liver transplantation for HCC. DCP is a useful tumor marker in the diagnosis and postoperative monitoring of patients with HCC
Timelike self-similar spherically symmetric perfect-fluid models
Einstein's field equations for timelike self-similar spherically symmetric
perfect-fluid models are investigated. The field equations are rewritten as a
first-order system of autonomous differential equations. Dimensionless
variables are chosen in such a way that the number of equations in the coupled
system is reduced as far as possible and so that the reduced phase space
becomes compact and regular. The system is subsequently analysed qualitatively
using the theory of dynamical systems.Comment: 23 pages, 6 eps-figure
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