Gravitational-Wave Constraints on the Progenitors of Fast Radio Bursts

The nature of fast radio bursts (FRBs) remains enigmatic. Highly energetic radio pulses of millisecond duration, FRBs are observed with dispersion measures consistent with an extragalactic source. A variety of models have been proposed to explain their origin. One popular class of theorized FRB progenitor is the coalescence of compact binaries composed of neutron stars and/or black holes. Such coalescence events are strong gravitational-wave emitters. We demonstrate that measurements made by the LIGO and Virgo gravitational-wave observatories can be leveraged to severely constrain the validity of FRB binary coalescence models. Existing measurements constrain the binary black hole rate to approximately $5\%$ of the FRB rate, and results from Advanced LIGO's O1 and O2 observing runs may place similarly strong constraints on the fraction of FRBs due to binary neutron star and neutron star--black hole progenitors.Comment: 5 pages, 2 figures, published in ApJL. Additional minor updates to match published version, updating metadat

Gravitational-Wave Geodesy: A New Tool for Validating Detection of the Stochastic Gravitational-Wave Background

A valuable target for advanced gravitational-wave detectors is the stochastic gravitational-wave background. The stochastic background imparts a weak correlated signal into networks of gravitational-wave detectors, and so standard searches for the gravitational-wave background rely on measuring cross-correlations between pairs of widely-separated detectors. Stochastic searches, however, can be affected by any other correlated effects which may also be present, including correlated frequency combs and magnetic Schumann resonances. As stochastic searches become sensitive to ever-weaker signals, it is increasingly important to develop methods to separate a true astrophysical signal from other spurious and/or terrestrial signals. Here, we describe a novel method to achieve this goal -- gravitational-wave geodesy. Just as radio geodesy allows for the localization of radio telescopes, so too can observations of the gravitational-wave background be used to infer the positions and orientations of gravitational-wave detectors. By demanding that a true observation of the gravitational-wave background yield constraints consistent with the baseline's known geometry, we demonstrate that we can successfully validate true observations of the gravitational-wave background while rejecting spurious signals due to correlated terrestrial effects.Comment: Minor typos correcte

Compassion Predictors in Undergraduates: A Catholic College Example

Compassion is sorely needed in contemporary society, including within faith-based colleges. Past research has examined the prevention of compassion fatigue in healthcare professions, but relatively little research exists on the predictors of compassion, particularly among student populations. This study examines the factors associated with higher compassion levels in graduating college seniors, revealing demographic, experiential, and beliefrelated factors contributing to compassion. Results suggest that the general profile of a highly compassionate graduating college senior is a student who is female, politically liberal, religious, studying the natural or social sciences, actively involved in community service or volunteering, and who has undergone workshops on racial/cultural awareness and sensitivity

A Parameter-Free Tour of the Binary Black Hole Population

The continued operation of the Advanced LIGO and Advanced Virgo gravitational-wave detectors is enabling the first detailed measurements of the mass, spin, and redshift distributions of the merging binary black hole population. Our present knowledge of these distributions, however, is based largely on strongly parameteric models; such models typically assume the distributions of binary parameters to be superpositions of power laws, peaks, dips, and breaks, and then measure the parameters governing these "building block" features. Although this approach has yielded great progress in initial characterization of the compact binary population, the strong assumptions entailed leave it often unclear which physical conclusions are driven by observation and which by the specific choice of model. In this paper, we instead model the merger rate of binary black holes as an unknown autoregressive process over the space of binary parameters, allowing us to measure the distributions of binary black hole masses, redshifts, component spins, and effective spins with near-complete agnosticism. We find the primary mass spectrum of binary black holes to be doubly-peaked, with a fairly flat continuum that steepens at high masses. We identify signs of unexpected structure in the redshift distribution of binary black holes: a uniform-in-comoving volume merger rate at low redshift followed by a rise in the merger rate beyond redshift $z\approx 0.5$. Finally, we find that the distribution of black hole spin magnitudes is unimodal and concentrated at small but non-zero values, and that spin orientations span a wide range of spin-orbit misalignment angles but are also unlikely to be truly isotropic.Comment: 24 pages, 14 figures; code can be found at http://github.com/tcallister/autoregressive-bbh-inference and data can be download from https://zenodo.org/record/761609

First search for a stochastic gravitational-wave background from ultralight bosons

Ultralight bosons with masses in the range 10^(−13)  eV ≤ m_b ≤ 10^(−12)  eV can induce a superradiant instability around spinning black holes (BHs) with masses of order 10−100  M⊙. This instability leads to the formation of a rotating “bosonic cloud” around the BH, which can emit gravitational waves (GWs) in the frequency band probed by ground-based detectors. The superposition of GWs from all such systems can generate a stochastic gravitational-wave background (SGWB). In this work, we develop a Bayesian data analysis framework to study the SGWB from bosonic clouds using data from Advanced LIGO and Advanced Virgo, building on previous work by Brito et al. [Phys. Rev. D 96, 064050 (2017)]. We further improve this model by adding a BH population of binary merger remnants. To assess the performance of our pipeline, we quantify the range of boson masses that can be constrained by Advanced LIGO and Advanced Virgo measurements at design sensitivity. Furthermore, we explore our capability to distinguish an ultralight boson SGWB from a stochastic signal due to distant compact binary coalescences (CBC). Finally, we present results of a search for the SGWB from bosonic clouds using data from Advanced LIGO’s first observing run. We find no evidence of such a signal. Due to degeneracies between the boson mass and unknown astrophysical quantities such as the distribution of isolated BH spins, our analysis cannot robustly exclude the presence of a bosonic field at any mass. Nevertheless, we show that under optimistic assumptions about the BH formation rate and spin distribution, boson masses in the range 2.0×10^(−13)  eV ≤ m_b ≤ 3.8×10^(−13)  eV are excluded at 95% credibility, although with less optimistic spin distributions, no masses can be excluded. The framework established here can be used to learn about the nature of fundamental bosonic fields with future gravitational wave observations

Compassion development in higher education

Many schools of psychology and religious studies intend to promote the cultivation of compassion. Compassion is currently an integral area of study in psychology, religious studies, and higher education, specifically in faith-based higher education. While secular universities in the United States strive to generate disciplinary-based knowledge through scholarship, their ability to promote students\u27 use of the information they are learning to create positive social change has typically lagged. Conscious of the magnitude of today\u27s global issues and dissatisfied with the current disparity between the world\u27s reality and university curricula, scholars have begun to re-imagine the role of higher education in forming the leaders who will face our most exigent problems. The present article reviews how compassion can be integrated into university curriculum, specifically in faith-based institutions. The article also discusses how compassion can be measured throughout the course of undergraduates\u27 careers

Polarization-based Tests of Gravity with the Stochastic Gravitational-Wave Background

The direct observation of gravitational waves with Advanced LIGO and Advanced Virgo offers novel opportunities to test general relativity in strong-field, highly dynamical regimes. One such opportunity is the measurement of gravitational-wave polarizations. While general relativity predicts only two tensor gravitational-wave polarizations, general metric theories of gravity allow for up to four additional vector and scalar modes. The detection of these alternative polarizations would represent a clear violation of general relativity. The LIGO-Virgo detection of the binary black hole merger GW170814 has recently offered the first direct constraints on the polarization of gravitational waves. The current generation of ground-based detectors, however, is limited in its ability to sensitively determine the polarization content of transient gravitational-wave signals. Observation of the stochastic gravitational-wave background, in contrast, offers a means of directly measuring generic gravitational-wave polarizations. The stochastic background, arising from the superposition of many individually unresolvable gravitational-wave signals, may be detectable by Advanced LIGO at design-sensitivity. In this paper, we present a Bayesian method with which to detect and characterize the polarization of the stochastic background. We explore prospects for estimating parameters of the background, and quantify the limits that Advanced LIGO can place on vector and scalar polarizations in the absence of a detection. Finally, we investigate how the introduction of new terrestrial detectors like Advanced Virgo aid in our ability to detect or constrain alternative polarizations in the stochastic background. We find that, although the addition of Advanced Virgo does not notably improve detection prospects, it may dramatically improve our ability to estimate the parameters of backgrounds of mixed polarization.Comment: 24 pages, 20 figures; Accepted by PRX. This version includes major changes in response to referee comments and corrects an error in Eq. E