2667484
Investigating the effect of precession on searches for neutron-star-black-hole binaries with Advanced LIGO
The first direct detection of neutron-star– black-hole binaries will likely be made with gravitational-wave observatories. Advanced LIGO and Advanced Virgo will be able to observe neutron-star– black-hole mergers at a maximum distance of 900 Mpc. To achieve this sensitivity, gravitational-wave searches will rely on using a bank of filter waveforms that accurately model the expected gravitational-wave signal. The emitted signal will depend on the masses of the black hole and the neutron star and also the angular momentum of both components. The angular momentum of the black hole is expected to be comparable to the orbital angular momentum when the system is emitting gravitational waves in Advanced LIGO’s and Advanced Virgo’s sensitive band. This angular momentum will affect the dynamics of the inspiralling system and alter the phase evolution of the emitted gravitational-wave signal. In addition, if the black hole’s angular momentum is not aligned with the orbital angular momentum, it will cause the orbital plane of the system to precess. In this work we demonstrate that if the effect of the black hole’s angular momentum is neglected in the waveform models used in gravitational-wave searches, the detection rate of (10+1.4)M_⊙ neutron-star– black-hole systems with isotropic spin distributions would be reduced by 33%–37% in comparison to a hypothetical perfect search at a fixed signal-to-noise ratio threshold. The error in this measurement is due to uncertainty in the post-Newtonian approximations that are used to model the gravitational-wave signal of neutron-star– black-hole inspiralling binaries. We describe a new method for creating a bank of filter waveforms where the black hole has nonzero angular momentum that is aligned with the orbital angular momentum. With this bank we find that the detection rate of (10+1.4)M_⊙ neutron-star– black-hole systems would be reduced by 26%–33%. Systems that will not be detected are ones where the precession of the orbital plane causes the gravitational-wave signal to match poorly with nonprecessing filter waveforms. We identify the regions of parameter space where such systems occur and suggest methods for searching for highly precessing neutron-star– black-hole binaries.
2754505
Using the inspiral program to search for gravitational waves from low-mass binary inspiral
The INSPIRAL program is the LIGO Scientific Collaboration's computational engine for the search for gravitational waves from binary neutron stars and sub-solar mass black holes. We describe how this program, which makes use of the FINDCHIRP algorithm, is integrated into a sophisticated data analysis pipeline that was used in the search for low-mass binary inspirals in data taken during the second LIGO science run.
42670702
Accuracy of gravitational waveform models for observing neutron-star–black-hole binaries in Advanced LIGO
Gravitational waves radiated by the coalescence of compact-object binaries containing a neutron star and a black hole are one of the most interesting sources for the ground-based gravitational-wave observatories Advanced LIGO and Advanced Virgo. Advanced LIGO will be sensitive to the inspiral of a 1.4M⊙ neutron star into a 10M⊙ black hole to a maximum distance of ∼900  Mpc. Achieving this sensitivity and extracting the physics imprinted in observed signals requires accurate modeling of the binary to construct template waveforms. In a neutron-star–black-hole binary, the black hole may have significant angular momentum (spin), which affects the phase evolution of the emitted gravitational waves. We investigate the ability of currently available post-Newtonian templates to model the gravitational waves emitted during the inspiral phase of neutron-star–black-hole binaries. We restrict to the case where the spin of the black hole is aligned with the orbital angular momentum and compare several post-Newtonian approximants. We examine restricted amplitude post-Newtonian waveforms that are accurate to third-and-a-half post-Newtonian order in the orbital dynamics and complete to second-and-a-half post-Newtonian order in the spin dynamics. We also consider post-Newtonian waveforms that include the recently derived third-and-a-half post-Newtonian order spin-orbit correction and the third post-Newtonian order spin-orbit tail correction. We compare these post-Newtonian approximants to the effective-one-body waveforms for spin-aligned binaries. For all of these waveform families, we find that there is a large disagreement between different waveform approximants, starting at low to moderate black hole spins, particularly for binaries where the spin is antialigned with the orbital angular momentum. The match between the TaylorT4 and TaylorF2 approximants is ∼0.8 for a binary with m_BH/m_NS∼4 and χ_BH = cJ_BH/Gm^(2)_(BH)∼0.4. We show that the divergence between the gravitational waveforms begins in the early inspiral at v∼0.2 for χ_BH∼0.4. Post-Newtonian spin corrections beyond those currently known will be required for optimal detection searches and to measure the parameters of neutron-star–black-hole binaries. The strong dependence of the gravitational-wave signal on the spin dynamics will make it possible to extract significant astrophysical information from detected systems with Advanced LIGO and Advanced Virgo.
41266047
Model waveform accuracy standards for gravitational wave data analysis
Model waveforms are used in gravitational wave data analysis to detect and then to measure the properties of a source by matching the model waveforms to the signal from a detector. This paper derives accuracy standards for model waveforms which are sufficient to ensure that these data analysis applications are capable of extracting the full scientific content of the data, but without demanding excessive accuracy that would place undue burdens on the model waveform simulation community. These accuracy standards are intended primarily for broadband model waveforms produced by numerical simulations, but the standards are quite general and apply equally to such waveforms produced by analytical or hybrid analytical-numerical methods.
119254576
Effect of eccentricity on searches for gravitational waves from coalescing compact binaries in ground-based detectors
Inspiralling compact binaries are expected to circularize before their gravitational-wave signals reach the sensitive frequency band of ground-based detectors. Current searches for gravitational waves from compact binaries using the LIGO and Virgo detectors therefore use circular templates to construct matched filters. Binary formation models have been proposed which suggest that some systems detectable by the LIGO-Virgo network may have non-negligible eccentricity. We investigate the ability of the restricted 3.5 post-Newtonian order TaylorF2 template bank, used by LIGO and Virgo to search for gravitational waves from compact binaries with masses M{ or approx. 0.1, the loss in matched filter signal-to-noise ratio due to eccentricity can be significant and so templates which include eccentric effects will be required to perform optimal searches for suchmore » systems.« less
51807515
Data formats for numerical relativity waves
This document proposes data formats to exchange numerical relativity results, in particular gravitational waveforms. The primary goal is to further the interaction between gravitational-wave source modeling groups and the gravitational-wave data-analysis community. We present a simple and extendable format which is applicable to various kinds of gravitational wave sources including binaries of compact objects and systems undergoing gravitational collapse, but is nevertheless sufficiently general to be useful for other purposes.
119368956
Mu2e: a Muon to Electron Conversion Experiment at Fermilab
Abstract We present the status of Mu2e, a proposed experiment to measure the rate of muon to electron conversion in the field of a nucleus. The Mu2e experiment will be hosted by Fermilab at a new muon campus, using a new beamline to deliver protons to the muon generation target. Mu2e will use a series of three solenoids to collect, transport, stop, and analyze the muons produced when the 8 GeV pulsed proton beam from the booster hits the tungsten production target. The 200 nsec wide proton pulse is designed to have a ratio of out-of-time to in-time protons better than 10 − 10 , insuring a measurement time window of approximately 1 microsecond essentially free from beam pion background. A precision, low-mass straw tube tracker will measure electron momenta with a precision of 1/1000, allowing clean separation of the conversion signal from Decay In Orbit electrons, the principle experimental background. Extensive coverage of multi-layer scintillation counters will detect 99.99% of the cosmic muons which could generate fake signals. A crystal calorimeter will provide particle ID to further reduce backgrounds. Detailed simulations show a 3-year run with 7.56 × 10 17 stopped muons will allow a Single Event Sensitivity of 2 × 10 − 17 , allowing an estimated 90% confidence level sensitivity to R μ e of 6 × 10 − 17 , a four-orders of magnitude improvement over existing limits. The Mu2e schedule is technically limited, with commissioning beginning in 2019. Mu2e may also run at Project X with 10× higher luminosity using either an aluminum or titanium target after minimal upgrades.
124330538
Giant resonances observed in the scattering of 96- and 115-MeV alpha particles
Beams of 96- and 115-MeV $alpha$ particles were used to study the giant resonance region in 27 nuclei ranging from $sup 14$N to $sup 208$Pb. A prominent broad (GAMMA=3--7 MeV) peak is present in the spectra at an excitation energy of approx.63/A$sup 1$/$sup 3$ MeV for all nuclei studied with A> or =36. No such prominent peak is apparent for A<32. The angular distributions of the peak are characterized by an oscillatory behavior which is quite different from the monotonic behavior of the background. Distorted wave calculations with L=2 reproduce the experimental angular distributions quite well for most of the nuclei. Energy-weighted sum rule fractions range from 30--50% for the lighter targets to near 100% for the heavier targets. Distorted wave calculations with a breathing mode (L=0) form factor fail to reproduce the observed resonance strength by about a factor of 3 for all targets. The width of the peak is smallest for the closed shell nuclei $sup 40$Ca, $sup 90$Zr, $sup 144$Sm, and $sup 208$Pb. A small but significant broadening is observed in the rare-earth region of deformed nuclei. The giant dipole resonance is not appreciably excited for any of the targets. (AIP)
119056791
Boundary states and black hole entropy
A formal derivation of black hole entropy is given as a sum over boundary states. The boundary states are labeled by energy and momentum surface densities, and parametrized by the boundary metric. The sum over state labels is expressed as a functional integral with measure determined by the density of states. The sum over metrics is expressed as a functional integral with measure determined by the universal expression for the inverse temperature gradient at the horizon. The analysis applies to any stationary, nonextreme black hole in any theory of gravitational and matter fields.
119367319
Gravitational waves from the dynamical bar instability in a rapidly rotating star
A rapidly rotating, axisymmetric star can be dynamically unstable to an $m=2$ ``bar'' mode that transforms the star from a disk shape to an elongated bar. The fate of such a bar-shaped star is uncertain. Some previous numerical studies indicate that the bar is short lived, lasting for only a few bar-rotation periods, while other studies suggest that the bar is relatively long lived. This paper contains the results of a numerical simulation of a rapidly rotating $\ensuremath{\gamma}=5/3$ fluid star. The simulation shows that the bar shape is long lived: once the bar is established, the star retains this shape for more than 10-bar-rotation periods, through the end of the simulation. The results are consistent with the conjecture that a star will retain its bar shape indefinitely on a dynamical time scale, as long as its rotation rate exceeds the threshold for secular bar instability. The results are described in terms of a low-density neutron star, but can be scaled to represent, for example, a burned-out stellar core that is prevented from complete collapse by centrifugal forces. Estimates for the gravitational-wave signal indicate that a dynamically unstable neutron star in our galaxy can be detected easily by the first generation of ground based gravitational-wave detectors. The signal for an unstable neutron star in the Virgo cluster might be seen by the planned advanced detectors. The Newtonian-quadrupole approximation is used throughout this work.
1026408
Turduckening black holes: An Analytical and computational study
We provide a detailed analysis of several aspects of the turduckening technique for evolving black holes. At the analytical level we study the constraint propagation for a family of formulations of Einstein's field equations and identify under what conditions the turducken procedure is rigorously justified and under what conditions constraint violations will propagate to the outside of the black holes. We present high resolution spherically symmetric studies which verify our analytical predictions. Then we present three-dimensional simulations of single distorted black holes using different variations of the turduckening method and also the puncture method. We study the effect that these different methods have on the coordinate conditions, constraint violations, and extracted gravitational waves. We find that the waves agree up to small but nonvanishing differences, caused by escaping superluminal gauge modes. These differences become smaller with increasing detector location.