656 research outputs found
Intrinsic and extrinsic geometries of a tidally deformed black hole
A description of the event horizon of a perturbed Schwarzschild black hole is
provided in terms of the intrinsic and extrinsic geometries of the null
hypersurface. This description relies on a Gauss-Codazzi theory of null
hypersurfaces embedded in spacetime, which extends the standard theory of
spacelike and timelike hypersurfaces involving the first and second fundamental
forms. We show that the intrinsic geometry of the event horizon is invariant
under a reparameterization of the null generators, and that the extrinsic
geometry depends on the parameterization. Stated differently, we show that
while the extrinsic geometry depends on the choice of gauge, the intrinsic
geometry is gauge invariant. We apply the formalism to solutions to the vacuum
field equations that describe a tidally deformed black hole. In a first
instance we consider a slowly-varying, quadrupolar tidal field imposed on the
black hole, and in a second instance we examine the tide raised during a close
parabolic encounter between the black hole and a small orbiting body.Comment: 27 pages, 4 figure
Resonant Shattering of Neutron Star Crusts
The resonant excitation of neutron star (NS) modes by tides is investigated
as a source of short gamma-ray burst (sGRB) precursors. We find that the
driving of a crust-core interface mode can lead to shattering of the NS crust,
liberating ~10^46-10^47 erg of energy seconds before the merger of a NS-NS or
NS-black hole binary. Such properties are consistent with Swift/BAT detections
of sGRB precursors, and we use the timing of the observed precursors to place
weak constraints on the crust equation of state. We describe how a larger
sample of precursor detections could be used alongside coincident gravitational
wave detections of the inspiral by Advanced LIGO class detectors to probe the
NS structure. These two types of observations nicely complement one another,
since the former constrains the equation of state and structure near the
crust-core boundary, while the latter is more sensitive to the core equation of
state.Comment: 5 pages, 2 figures. Accepted to PR
Tidal deformability of neutron stars with realistic equations of state and their gravitational wave signatures in binary inspiral
The early part of the gravitational wave signal of binary neutron star
inspirals can potentially yield robust information on the nuclear equation of
state. The influence of a star's internal structure on the waveform is
characterized by a single parameter: the tidal deformability lambda, which
measures the star's quadrupole deformation in response to the companion's
perturbing tidal field. We calculate lambda for a wide range of equations of
state and find that the value of lambda spans an order of magnitude for the
range of equation of state models considered.
An analysis of the feasibility of discriminating between neutron star
equations of state with gravitational wave observations of the early part of
the inspiral reveals that the measurement error in lambda increases steeply
with the total mass of the binary. Comparing the errors with the expected range
of lambda, we find that Advanced LIGO observations of binaries at a distance of
100 Mpc will probe only unusually stiff equations of state, while the proposed
Einstein Telescope is likely to see a clean tidal signature.Comment: 12 pages, submitted to PR
Repatriation Adjustment, Job Satisfaction, and Turnover Intentions as a Function of Core Self-Evaluations and Role Clarity
A growing corpus of employee relocation literature proposes the construct of repatriation work adjustment as not only a desired outcome on behalf of returning employees and their organizations, but also a persistent challenge. Contemporary research consistently traces repatriation work adjustment to a wide range of individual, occupational, and cultural antecedents, while also hypothesizing it as a contributor to desired outcomes. However, there exists a dearth of literature examining the intermediary role of job factors in the relationship between individual differences and repatriation work adjustment. By examining the main and indirect effects of core self-evaluations and role clarity, the present study proposes several hypotheses to determine whether core self-evaluations affect repatriation work adjustment through role clarity, and whether repatriation work adjustment affects job satisfaction and intentions to turnover. To test these mediated models, this study used an online, survey-based design to obtain self-report data from a sample of repatriated employees
Forced motion near black holes
We present two methods for integrating forced geodesic equations in the Kerr
spacetime, which can accommodate arbitrary forces. As a test case, we compute
inspirals under a simple drag force, mimicking the presence of gas. We verify
that both methods give the same results for this simple force. We find that
drag generally causes eccentricity to increase throughout the inspiral. This is
a relativistic effect qualitatively opposite to what is seen in
gravitational-radiation-driven inspirals, and similar to what is observed in
hydrodynamic simulations of gaseous binaries. We provide an analytic
explanation by deriving the leading order relativistic correction to the
Newtonian dynamics. If observed, an increasing eccentricity would provide clear
evidence that the inspiral was occurring in a non-vacuum environment. Our two
methods are especially useful for evolving orbits in the adiabatic regime. Both
use the method of osculating orbits, in which each point on the orbit is
characterized by the parameters of the geodesic with the same instantaneous
position and velocity. Both methods describe the orbit in terms of the geodesic
energy, axial angular momentum, Carter constant, azimuthal phase, and two
angular variables that increase monotonically and are relativistic
generalizations of the eccentric anomaly. The two methods differ in their
treatment of the orbital phases and the representation of the force. In one
method the geodesic phase and phase constant are evolved together as a single
orbital phase parameter, and the force is expressed in terms of its components
on the Kinnersley orthonormal tetrad. In the second method, the phase constants
of the geodesic motion are evolved separately and the force is expressed in
terms of its Boyer-Lindquist components. This second approach is a
generalization of earlier work by Pound and Poisson for planar forces in a
Schwarzschild background.Comment: 28 pages, 2 figures, submitted to Phys. Rev. D; v2 has minor changes
for consistency with published version, plus a new section discussing the
relative advantages of the two approache
Post-1-Newtonian tidal effects in the gravitational waveform from binary inspirals
The gravitational wave signal from an inspiralling binary neutron star system
will contain detailed information about tidal coupling in the system, and thus,
about the internal physics of the neutron stars. To extract this information
will require highly accurate models for the gravitational waveform. We present
here a calculation of the gravitational wave signal from a binary with
quadrupolar tidal interactions which includes all post-1-Newtonian-order
effects in both the conservative dynamics and wave generation. We consider
stars with adiabatically induced quadrupoles moving in circular orbits, and
work to linear in the stars' quadrupole moments. We find that post-1-Newtonian
corrections increase the tidal signal by approximately 20% at gravitational
wave frequencies of 400 Hz.Comment: 7 page
Semianalytical estimates of scattering thresholds and gravitational radiation in ultrarelativistic black hole encounters
Ultrarelativistic collisions of black holes are ideal gedanken experiments to
study the nonlinearities of general relativity. In this paper we use
semianalytical tools to better understand the nature of these collisions and
the emitted gravitational radiation. We explain many features of the energy
spectra extracted from numerical relativity simulations using two complementary
semianalytical calculations. In the first calculation we estimate the radiation
by a "zero-frequency limit" analysis of the collision of two point particles
with finite impact parameter. In the second calculation we replace one of the
black holes by a point particle plunging with arbitrary energy and impact
parameter into a Schwarzschild black hole, and we explore the multipolar
structure of the radiation paying particular attention to the near-critical
regime. We also use a geodesic analogy to provide qualitative estimates of the
dependence of the scattering threshold on the black hole spin and on the
dimensionality of the spacetime.Comment: 29 pages, 19 figure, 6 tables, minor changes to match version in
press in Phys.Rev.
Effective source approach to self-force calculations
Numerical evaluation of the self-force on a point particle is made difficult
by the use of delta functions as sources. Recent methods for self-force
calculations avoid delta functions altogether, using instead a finite and
extended "effective source" for a point particle. We provide a review of the
general principles underlying this strategy, using the specific example of a
scalar point charge moving in a black hole spacetime. We also report on two new
developments: (i) the construction and evaluation of an effective source for a
scalar charge moving along a generic orbit of an arbitrary spacetime, and (ii)
the successful implementation of hyperboloidal slicing that significantly
improves on previous treatments of boundary conditions used for
effective-source-based self-force calculations. Finally, we identify some of
the key issues related to the effective source approach that will need to be
addressed by future work.Comment: Invited review for NRDA/Capra 2010 (Theory Meets Data Analysis at
Comparable and Extreme Mass Ratios), Perimeter Institute, June 2010, CQG
special issue - 22 pages, 8 figure
Specific heat of MgB_2 after irradiation
We studied the effect of disorder on the superconducting properties of
polycrystalline MgB_2 by specific-heat measurements. In the pristine state,
these measurements give a bulk confirmation of the presence of two
superconducting gaps with 2 Delta 0 / k_B T_c = 1.3 and 3.9 with nearly equal
weights. The scattering introduced by irradiation suppresses T_c and tends to
average the two gaps although less than predicted by theory. We also found that
by a suitable irradiation process by fast neutrons, a substantial bulk increase
of dH_{c2}/dT at T_c can be obtained without sacrificing more than a few
degrees in T_c. The upper critical field of the sample after irradiation
exceeds 28 T at T goes to 0 K.Comment: 11 pages text, 6 figures, accepted by Journal of Physics: Condensed
Matte
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