3,062 research outputs found
Comparing Effective-One-Body gravitational waveforms to accurate numerical data
We continue the program of constructing, within the Effective-One-Body (EOB)
approach, high accuracy, faithful analytic waveforms describing the
gravitational wave signal emitted by inspiralling and coalescing binary black
holes (BHs). We present the comparable-mass version of a new, resummed
3PN-accurate EOB quadrupolar waveform recently introduced in the
small-mass-ratio limit. We compare the phase and the amplitude of this waveform
to the recently published results of a high-accuracy numerical relativity (NR)
simulation of 15 orbits of an inspiralling equal-mass binary BHs system
performed by the Caltech-Cornell group. We find a remarkable agreement, both in
phase and in amplitude, between the new EOB waveform and the published
numerical data. More precisely: (i) in the gravitational wave (GW) frequency
domain where the phase of one of the non-resummed ``Taylor
approximant'' (T4) waveform matches well with the numerical relativity one, we
find that the EOB phase fares as well, while (ii) for higher GW frequencies,
, where the TaylorT4 approximant starts to
significantly diverge from the NR phase, we show that the EOB phase continues
to match well the NR one. We further propose various methods of tuning the two
inspiral flexibility parameters, and , of the EOB waveform
so as to ``best fit'' EOB predictions to numerical data. We find that the
maximal dephasing between EOB and NR can then be reduced below GW
cycles over the entire span (30 GW cycles) of the simulation. Our resummed EOB
amplitude agrees much better with the NR one than any of the previously
considered non-resummed, post-Newtonian one.Comment: 15 pages, 7 figures, submitted to Phys. Rev. D. Revised version.
Figs. 2-7 improved. Slight changes in a few numbers. One reference adde
The rent's too high: Self-archive for fair online publication costs
The main contributors of scientific knowledge, researchers, generally aim to
disseminate their findings far and wide. And yet, publishing companies have
largely kept these findings behind a paywall. With digital publication
technology markedly reducing cost, this enduring wall seems disproportionate
and unjustified; moreover, it has sparked a topical exchange concerning how to
modernize academic publishing. This discussion, however, seems to focus on how
to compensate major publishers for providing open access through a "pay to
publish" model, in turn transferring financial burdens from libraries to
authors and their funders. Large publishing companies, including Elsevier,
Springer Nature, Wiley, PLoS, and Frontiers, continue to earn exorbitant
revenues each year, hundreds of millions of dollars of which now come from
processing charges for open-access articles. A less expensive and equally
accessible alternative exists: widespread self-archiving of peer-reviewed
articles. All we need is awareness of this alternative and the will to employ
itComment: 8 pages, 1 figure, 19 reference
Gravitational Self Force in a Schwarzschild Background and the Effective One Body Formalism
We discuss various ways in which the computation of conservative
Gravitational Self Force (GSF) effects on a point mass moving in a
Schwarzschild background can inform us about the basic building blocks of the
Effective One-Body (EOB) Hamiltonian. We display the information which can be
extracted from the recently published GSF calculation of the first-GSF-order
shift of the orbital frequency of the last stable circular orbit, and we
combine this information with the one recently obtained by comparing the EOB
formalism to high-accuracy numerical relativity (NR) data on coalescing binary
black holes. The information coming from GSF data helps to break the degeneracy
(among some EOB parameters) which was left after using comparable-mass NR data
to constrain the EOB formalism. We suggest various ways of obtaining more
information from GSF computations: either by studying eccentric orbits, or by
focussing on a special zero-binding zoom-whirl orbit. We show that logarithmic
terms start entering the post-Newtonian expansions of various (EOB and GSF)
functions at the fourth post-Newtonian (4PN) level, and we analytically compute
the first logarithm entering a certain, gauge-invariant "redshift" GSF function
(defined along the sequence of circular orbits).Comment: 44 page
Analysis of polyubiquitin conjugates reveals that the Rpn10 substrate receptor contributes to the turnover of multiple proteasome targets
The polyubiquitin receptor Rpn10 targets ubiquitylated Sic1 to the 26S proteasome for degradation. In contrast, turnover of at least one ubiquitin-proteasome system (UPS) substrate, CPY*, is impervious to deletion of RPN10. To distinguish whether RPN10 is involved in the turnover of only a small set of cell cycle regulators that includes Sic1 or plays a more general role in the UPS, we sought to develop a general method that would allow us to survey the spectrum of ubiquitylated proteins that selectively accumulate in rpn10 cells. Polyubiquitin conjugates from yeast cells that express hexahistidine-tagged ubiquitin (H6-ubiquitin) were first enriched on a polyubiquitin binding protein affinity resin. This material was then denatured and subjected to IMAC to retrieve H6-ubiquitin and proteins to which it may be covalently linked. Using this approach, we identified 127 proteins that are candidate substrates for the 26S proteasome. We then sequenced ubiquitin conjugates from cells lacking Rpn10 (rpn10) and identified 54 proteins that were uniquely recovered from rpn10 cells. These include two known targets of the UPS, the cell cycle regulator Sic1 and the transcriptional activator Gcn4. Our approach of comparing the ubiquitin conjugate proteome in wild-type and mutant cells has the resolving power to identify even an extremely inabundant transcriptional regulatory protein and should be generally applicable to mapping enzyme substrate networks in the UPS
Measurability of the tidal polarizability of neutron stars in late-inspiral gravitational-wave signals
The gravitational wave signal from a binary neutron star inspiral contains
information on the nuclear equation of state. This information is contained in
a combination of the tidal polarizability parameters of the two neutron stars
and is clearest in the late inspiral, just before merger. We use the recently
defined tidal extension of the effective one-body formalism to construct a
controlled analytical description of the frequency-domain phasing of neutron
star inspirals up to merger. Exploiting this analytical description we find
that the tidal polarizability parameters of neutron stars can be measured by
the advanced LIGO-Virgo detector network from gravitational wave signals having
a reasonable signal-to-noise ratio of . This measurability result
seems to hold for all the nuclear equations of state leading to a maximum mass
larger than . We also propose a promising new way of extracting
information on the nuclear equation of state from a coherent analysis of an
ensemble of gravitational wave observations of separate binary merger events.Comment: 28 pages, 6 figures. Submitted to Phys. Rev.
Symmetries,Singularities and the De-Emergence of Space
Recent work has revealed intriguing connections between a
Belinsky-Khalatnikov-Lifshitz-type analysis of spacelike singularities in
General Relativity and certain infinite dimensional Lie algebras, and in
particular the `maximally extended' hyperbolic Kac--Moody algebra E10. In this
essay we argue that these results may lead to an entirely new understanding of
the (quantum) nature of space(-time) at the Planck scale, and hence -- via an
effective `de-emergence' of space near a singularity -- to a novel mechanism
for achieving background independence in quantum gravity.Comment: 10 page
Transition from inspiral to plunge in precessing binaries of spinning black holes
We investigate the non-adiabatic dynamics of spinning black hole binaries by
using an analytical Hamiltonian completed with a radiation-reaction force,
containing spin couplings, which matches the known rates of energy and angular
momentum losses on quasi-circular orbits. We consider both a straightforward
post-Newtonian-expanded Hamiltonian (including spin-dependent terms), and a
version of the resummed post-Newtonian Hamiltonian defined by the Effective
One-Body approach. We focus on the influence of spin terms onto the dynamics
and waveforms. We evaluate the energy and angular momentum released during the
final stage of inspiral and plunge. For an equal-mass binary the energy
released between 40Hz and the frequency beyond which our analytical treatment
becomes unreliable is found to be, when using the more reliable Effective
One-Body dynamics: 0.6% M for anti-aligned maximally spinning black holes, 5% M
for aligned maximally spinning black hole, and 1.8% M for non-spinning
configurations. In confirmation of previous results, we find that, for all
binaries considered, the dimensionless rotation parameter J/E^2 is always
smaller than unity at the end of the inspiral, so that a Kerr black hole can
form right after the inspiral phase. By matching a quasi-normal mode ringdown
to the last reliable stages of the plunge, we construct complete waveforms
approximately describing the gravitational wave signal emitted by the entire
process of coalescence of precessing binaries of spinning black holes.Comment: 31 pages, 7 tables, and 13 figure
The Psychology of Neurofeedback: Clinical Intervention Even if Applied Placebo
Advocates of neurofeedback make bold claims concerning brain regulation, treatment of disorders, and mental health. Decades of research and thousands of peer-reviewed publications support neurofeedback using electroencephalography (EEG-nf); yet, few experiments isolate the act of receiving feedback from a specific brain signal as a necessary precursor to obtain the purported benefits. Moreover, while psychosocial parameters including participant motivation and expectation, rather than neurobiological substrates, seem to fuel clinical improvement across a wide range of disorders, for-profit clinics continue to sprout across North America and Europe. Here, we highlight the tenuous evidence supporting EEG-nf and sketch out the weaknesses of this approach. We challenge classic arguments often articulated by proponents of EEG-nf and underscore how psychologists and mental health professionals stand to benefit from studying the ubiquitous placebo influences that likely drive these treatment outcomes
Gravitational self-force and the effective-one-body formalism between the innermost stable circular orbit and the light ring
We compute the conservative piece of the gravitational self-force (GSF)
acting on a particle of mass m_1 as it moves along an (unstable) circular
geodesic orbit between the innermost stable circular orbit (ISCO) and the light
ring of a Schwarzschild black hole of mass m_2>> m_1. More precisely, we
construct the function h_{uu}(x) = h_{\mu\nu} u^{\mu} u^{\nu} (related to
Detweiler's gauge-invariant "redshift" variable), where h_{\mu\nu} is the
regularized metric perturbation in the Lorenz gauge, u^{\mu} is the
four-velocity of m_1, and x= [Gc^{-3}(m_1+m_2)\Omega]^{2/3} is an invariant
coordinate constructed from the orbital frequency \Omega. In particular, we
explore the behavior of h_{uu} just outside the "light ring" at x=1/3, where
the circular orbit becomes null. Using the recently discovered link between
h_{uu} and the piece a(u), linear in the symmetric mass ratio \nu, of the main
radial potential A(u,\nu) of the Effective One Body (EOB) formalism, we compute
a(u) over the entire domain 0<u<1/3. We find that a(u) diverges at the
light-ring as ~0.25 (1-3u)^{-1/2}, explain the physical origin of this
divergence, and discuss its consequences for the EOB formalism. We construct
accurate global analytic fits for a(u), valid on the entire domain 0<u<1/3 (and
possibly beyond), and give accurate numerical estimates of the values of a(u)
and its first 3 derivatives at the ISCO, as well as the O(\nu) shift in the
ISCO frequency. In previous work we used GSF data on slightly eccentric orbits
to compute a certain linear combination of a(u) and its first two derivatives,
involving also the O(\nu) piece \bar d(u) of a second EOB radial potential
{\bar D}(u,\nu). Combining these results with our present global analytic
representation of a(u), we numerically compute {\bar d}(u)$ on the interval
0<u\leq 1/6.Comment: 44 pages, 8 figures. Extended discussion in Section V and minor
typographical corrections throughout. Version to be published in PR
Effective action approach to higher-order relativistic tidal interactions in binary systems and their effective one body description
The gravitational-wave signal from inspiralling neutron-star--neutron-star
(or black-hole--neutron-star) binaries will be influenced by tidal coupling in
the system. An important science goal in the gravitational-wave detection of
these systems is to obtain information about the equation of state of neutron
star matter via the measurement of the tidal polarizability parameters of
neutron stars. To extract this piece of information will require to have
accurate analytical descriptions of both the motion and the radiation of
tidally interacting binaries. We improve the analytical description of the late
inspiral dynamics by computing the next-to-next-to-leading order relativistic
correction to the tidal interaction energy. Our calculation is based on an
effective-action approach to tidal interactions, and on its transcription
within the effective-one-body formalism. We find that second-order relativistic
effects (quadratic in the relativistic gravitational potential ) significantly increase the effective tidal polarizability of
neutron stars by a distance-dependent amplification factor of the form where, say for an equal-mass binary,
(as previously known) and (as
determined here for the first time). We argue that higher-order relativistic
effects will lead to further amplification, and we suggest a Pad\'e-type way of
resumming them. We recommend to test our results by comparing
resolution-extrapolated numerical simulations of inspiralling-binary neutron
stars to their effective one body description.Comment: 29 pages, Physical Review D, to appea
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