364 research outputs found
Introduction
Virtually everyone agrees that the family is a vital institution. Because of the perceived importance of the family to the state, our society always has tried to regulate both the form and functions of families. Laws prescribe who may form a family, the rights and obligations of family members towards each other, and the substantive and procedural rules for dissolving families
Thinking About Public Policy Toward Abuse and Neglect of Children: A Review of \u3cem\u3eBefore the Best Interests of the Child\u3c/em\u3e
A review of Before the Best Interests of the Child by Joseph Goldstein, Anna Freud, and Albert J. Solni
On Toroidal Horizons in Binary Black Hole Inspirals
We examine the structure of the event horizon for numerical simulations of
two black holes that begin in a quasicircular orbit, inspiral, and finally
merge. We find that the spatial cross section of the merged event horizon has
spherical topology (to the limit of our resolution), despite the expectation
that generic binary black hole mergers in the absence of symmetries should
result in an event horizon that briefly has a toroidal cross section. Using
insight gained from our numerical simulations, we investigate how the choice of
time slicing affects both the spatial cross section of the event horizon and
the locus of points at which generators of the event horizon cross. To ensure
the robustness of our conclusions, our results are checked at multiple
numerical resolutions. 3D visualization data for these resolutions are
available for public access online. We find that the structure of the horizon
generators in our simulations is consistent with expectations, and the lack of
toroidal horizons in our simulations is due to our choice of time slicing.Comment: Submitted to Phys. Rev.
Gravitational-Wave Signature of an Inspiral into a Supermassive Horizonless Object
Event horizons are among the most intriguing of general relativity's
predictions. Although on firm theoretical footing, direct indications of their
existence have yet to be observed. With this motivation in mind, we explore
here the possibility of finding a signature for event horizons in the
gravitational waves (GWs) produced during the inspiral of stellar-mass compact
objects (COs) into the supermassive () objects that lie at
the center of most galaxies. Such inspirals will be a major source for LISA,
the future space-based GW observatory. We contrast supermassive black holes
with models in which the central object is a supermassive boson star (SMBS).
Provided the COs interact only gravitationally with the SMBS, stable orbits
exist not just outside the Schwarzschild radius but also inside the surface of
the SMBS as well. The absence of an event horizon allows GWs from these orbits
to be observed. Here we solve for the metric in the interior of a fairly
generic class of SMBS and evolve the trajectory of an inspiraling CO from the
Schwarzschild exterior through the plunge into the exotic SMBS interior. We
calculate the approximate waveforms for GWs emitted during this inspiral.
Geodesics within the SMBS surface will exhibit extreme pericenter precession
and other features making the emitted GWs readily distinguishable from those
emitted during an inspiral into a black hole.Comment: 20 pages, 9 figures, submitted to PR
Divergences in the Effective Action for Acausal Spacetimes
The 1--loop effective Lagrangian for a massive scalar field on an arbitrary
causality violating spacetime is calculated using the methods of Euclidean
quantum field theory in curved spacetime. Fields of spin 1/2, spin 1 and
twisted field configurations are also considered. In general, we find that the
Lagrangian diverges to minus infinity at each of the nth polarised
hypersurfaces of the spacetime with a structure governed by a DeWitt-Schwinger
type expansion.Comment: 17 pages, Late
Black-Hole Spin Dependence in the Light Curves of Tidal Disruption Events
A star orbiting a supermassive black hole can be tidally disrupted if the
black hole's gravitational tidal field exceeds the star's self gravity at
pericenter. Some of this stellar tidal debris can become gravitationally bound
to the black hole, leading to a bright electromagnetic flare with bolometric
luminosity proportional to the rate at which material falls back to pericenter.
In the Newtonian limit, this flare will have a light curve that scales as
t^-5/3 if the tidal debris has a flat distribution in binding energy. We
investigate the time dependence of the black-hole mass accretion rate when
tidal disruption occurs close enough the black hole that relativistic effects
are significant. We find that for orbits with pericenters comparable to the
radius of the marginally bound circular orbit, relativistic effects can double
the peak accretion rate and halve the time it takes to reach this peak
accretion rate. The accretion rate depends on both the magnitude of the
black-hole spin and its orientation with respect to the stellar orbit; for
orbits with a given pericenter radius in Boyer-Lindquist coordinates, a maximal
black-hole spin anti-aligned with the orbital angular momentum leads to the
largest peak accretion rate.Comment: 16 pages, 15 figures, 1 table, PRD published versio
Aspects of Cosmic Inflation in Expanding Bose-Einstein Condensates
Phonons in expanding Bose-Einstein condensates with wavelengths much larger
than the healing length behave in the same way as quantum fields within a
universe undergoing an accelerated expansion. This analogy facilitates the
application of many tools and concepts known from general relativity (such as
horizons) and the prediction of the corresponding effects such as the freezing
of modes after horizon crossing and the associated amplification of quantum
fluctuations. Basically the same amplification mechanism is (according to our
standard model of cosmology) supposed to be responsible for the generation of
the initial inhomogeneities -- and hence the seeds for the formation of
structures such as our galaxy -- during cosmic inflation (i.e., a very early
epoch in the evolution of our universe). After a general discussion of the
analogy (\emph{analogue cosmology}), we calculate the frozen and amplified
density-density fluctuations for quasi-two dimensional (Q2D) and three
dimensional (3D) condensates which undergo a free expansion after switching off
the (longitudinal) trap. PACS: 03.75.Kk, 04.62.+v.Comment: 17 page
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