544 research outputs found
Structure of inert layer 4He adsorbed on a mesoporous silica
We have studied the structure of inert layer 4He adsorbed on mesoporous
silica (FSM-16), by the vapor pressure and heat capacity measurements. The heat
capacity shows a Schottky-like peak due to the excitation of a part of
localized solid to fluid. We analyzed the heat capacity over a wide temperature
region based on the model including the contribution of the localized solid and
excited fluid and clarified that the excited fluid coexists with the localized
solid at high temperature. As the areal density approaches the value at which
superfluid appears (n_C), the fluid amount is likely to go to zero, suggesting
a possibility that the inert layer is solidified just below n_C
Quasiequilibrium sequences of binary neutron stars undergoing dynamical scalarization
We calculate quasiequilibrium sequences of equal-mass, irrotational binary
neutron stars (BNSs) in a scalar-tensor (ST) theory of gravity that admits
dynamical scalarization. We model neutron stars with realistic equations of
state (notably through piecewise polytropic equations of state). Using these
quasiequilibrium sequences we compute the binary's scalar charge and binding
energy versus orbital angular frequency. We find that the absolute value of the
binding energy is smaller than in general relativity (GR), differing at most by
~14% at high frequencies for the cases considered. We use the newly computed
binding energy and the balance equation to estimate the number of
gravitational-wave (GW) cycles during the adiabatic, quasicircular inspiral
stage up to the end of the sequence, which is the last stable orbit or the
mass-shedding point, depending on which comes first. We find that, depending on
the ST parameters, the number of GW cycles can be substantially smaller than in
GR. In particular, we obtain that when dynamical scalarization sets in around a
GW frequency of ~130 Hz, the sole inclusion of the ST binding energy causes a
reduction of GW cycles from ~120 Hz up to the end of the sequence (~1200 Hz) of
~11% with respect to the GR case. We estimate that when the ST energy flux is
also included the reduction in GW cycles becomes of ~24%. Quite interestingly,
dynamical scalarization can produce a difference in the number of GW cycles
with respect to the GR point-particle case that is much larger than the effect
due to tidal interactions, which is on the order of only a few GW cycles. These
results further clarify and confirm recent studies that have evolved BNSs
either in full numerical relativity or in post-Newtonian theory, and point out
the importance of developing accurate ST-theory waveforms for systems composed
of strongly self-gravitating objects, such as BNSs.Comment: 16 pages, 14 figures, 2 tables, updated to match the published
versio
Location of the innermost stable circular orbit of binary neutron stars in the post Newtonian approximations of general relativity
In this paper, we present results obtained from our recent studies on the
location of the innermost stable circular orbit (ISCO) for binary neutron stars
(BNSs) in several levels of post Newtonian (PN) approximations. We reach the
following conclusion at present: (1) even in the Newtonian case, there exists
the ISCO for binary of sufficiently stiff equation of state (EOS). If the mass
and the radius of each star are fixed, the angular velocity at the ISCO
is larger for softer EOS: (2) when we include the first PN
correction, there appear roughly two kinds of effects. One is the effect to the
self-gravity of each star of binary and the other is to the gravity acting
between two stars. Due to the former one, each star of binary becomes compact
and the tidal effect is less effective. As a result, tends to
be increased. On the other hand, the latter one has the property to destabilize
the binary orbit, and tends to be decreased. If we take into
account both effects, however, the former effect is stronger than the latter
one, and becomes large with increase of the 1PN correction: (3)
the feature mentioned above is more remarkable for softer EOS if the mass and
radius are fixed. This is because for softer EOS, each star has the larger
central density and is susceptible to the GR correction: (4) there has been no
self consistent calculation including all the 2PN effects and only exist
studies in which one merely includes the effect of the 2PN gravity acting
between two stars. In this case, the effect has the property to destabilize the
binary orbit, so that is always smaller than that for the
Newtonian case. If we include the PN effect of the self-gravity to each star,
will increase.Comment: 33 pages ptptex file, 29 figures, to appear in Progress of
Theoretical Physics Supplement No.128 (1997) `Perturbative and Numerical
Approaches to Gravitational Radiation
Irrotational and Incompressible Ellipsoids in the First Post-Newtonian Approximation of General Relativity
First post-Newtonian (1PN) hydrostatic equations for an irrotational fluid
which have been recently derived are solved for an incompressible star. The 1PN
configurations are expressed as a deformation of the Newtonian irrotational
Riemann ellipsoid using Lagrangian displacement vectors introduced by
Chandrasekhar. For the 1PN solutions, we also calculate the luminosity of
gravitational waves in the 1PN approximation using the Blanchet-Damour
formalism. It is found that the solutions of the 1PN equations exhibit
singularities at points where the axial ratios of semi-axes are 1:0.5244:0.6579
and 1:0.2374:0.2963, and the singularities seem to show that at the points, the
irrotational Riemann ellipsoid is unstable to the deformation induced by the
effect of general relativity. For stable cases (a_2/a_1 > 0.5244, where a_1 and
a_2 are the semi-major and minor axes, respectively) we find that when
increasing the 1PN correction, the angular velocity and total angular momentum
increase, while the total energy and luminosity of gravitational waves
decrease. These 1PN solutions will be useful when examining the accuracy of
numerical code for obtaining relativistic irrotational stars.
We also investigate the validity of an ellipsoidal approximation, in which a
1PN solution is obtained assuming an ellipsoidal figure and neglecting the
deformation. It is found that for , the ellipsoidal
approximation gives a fairly accurate result for the energy, angular momentum,
and angular velocity, although in the approximation we cannot find the
singularities.Comment: 33 pages with 3 figures, ptptex, corrected some typos, tables and
figure
Coalescence of binary neutron stars in a scalar-tensor theory of gravity
We carry out numerical-relativity simulations of coalescing binary neutron
stars in a scalar-tensor theory that admits spontaneous scalarization. We model
neutron stars with realistic equations of state. We choose the free parameters
of the theory taking into account the constraints imposed by the latest
observations of neutron-star-- white-dwarf binaries with pulsar timing. We show
that even within those severe constraints, scalarization can still affect the
evolution of the binary neutron stars not only during the late inspiral, but
also during the merger stage. We also confirm that even when both neutron stars
have quite small scalar charge at large separations, they can be strongly
scalarized dynamically during the final stages of the inspiral. In particular,
we identify the binary parameters for which scalarization occurs either during
the late inspiral or only after the onset of the merger when a remnant,
supramassive or hypermassive neutron star is formed. We also discuss how those
results can impact the extraction of physical information on gravitational
waves once they are detected.Comment: 17 pages, 12 figure
Solidification of 4He confined in a nanometer-size channel
Solidification of 4He confined in a one-dimensional 2.8-nm channel of FSM was studied by pressure and heat capacity measurements. It was found that the freezing pressure in the channel is greatly elevated and is between 3.3 and 3.8 MPa at absolute zero. Furthermore, the density change at the liquid-solid transition is evaluated. The decrease in the molar volume is less than 1×10−2 cm3/mol at the transition of 4 MPa, which is about two orders of magnitude smaller than that of bulk. From this observation, we can conclude that solid 4He confined in the channel has a density as low as liquid
Neutrino transport in black hole-neutron star binaries: neutrino emission and dynamical mass ejection
We study the merger of black hole-neutron star binaries by fully
general-relativistic neutrino-radiation-hydrodynamics simulations throughout
the coalescence, particularly focusing on the role of neutrino irradiation in
dynamical mass ejection. Neutrino transport is incorporated by an approximate
transfer scheme based on the truncated moment formalism. While we fix the mass
ratio of the black hole to the neutron star to be 4 and the dimensionless spin
parameter of the black hole to be 0.75, the equations of state for
finite-temperature neutron-star matter are varied. The hot accretion disk
formed after tidal disruption of the neutron star emits a copious amount of
neutrinos with the peak total luminosity ~1--3x10^53 erg s^(-1) via thermal
pair production and subsequent electron/positron captures on free nucleons.
Nevertheless, the neutrino irradiation does not modify significantly the
electron fraction of the dynamical ejecta from the neutrinoless
beta-equilibrium value at zero temperature of initial neutron stars. The mass
of the wind component driven by neutrinos from the remnant disk is negligible
compared to the very neutron-rich dynamical component, throughout our
simulations performed until a few tens milliseconds after the onset of merger,
for the models considered in this study. These facts suggest that the ejecta
from black hole-neutron star binaries are very neutron rich and are expected to
accommodate strong r-process nucleosynthesis, unless magnetic or viscous
processes contribute substantially to the mass ejection from the disk. We also
find that the peak neutrino luminosity does not necessarily increase as the
disk mass increases, because tidal disruption of a compact neutron star can
result in a remnant disk with a small mass but high temperature.Comment: 17 pages, 16 figures, matched to the published versio
Frequency-domain gravitational waveform models for inspiraling binary neutron stars
We develop a model for frequency-domain gravitational waveforms from
inspiraling binary neutron stars. Our waveform model is calibrated by
comparison with hybrid waveforms constructed from our latest high-precision
numerical-relativity waveforms and the SEOBNRv2T waveforms in the frequency
range of --. We show that the phase difference between our
waveform model and the hybrid waveforms is always smaller than for the binary tidal deformability, , in the range
and for the mass ratio between 0.73
and 1. We show that, for --, the distinguishability for the
signal-to-noise ratio and the mismatch between our waveform model
and the hybrid waveforms are always smaller than 0.25 and ,
respectively. The systematic error of our waveform model in the measurement of
is always smaller than with respect to the hybrid
waveforms for . The statistical error
in the measurement of binary parameters is computed employing our waveform
model, and we obtain results consistent with the previous studies. We show that
the systematic error of our waveform model is always smaller than
(typically smaller than ) of the statistical error for events with the
signal-to-noise ratio of .Comment: 22 pages, 16 figures, accepted for publication in PR
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