Estimation of the Sensitive Volume for Gravitational-wave Source Populations Using Weighted Monte Carlo Integration

The population analysis and estimation of merger rates of compact binaries is one of the important topics in gravitational wave (GW) astronomy. The primary ingredient in these analyses is the population-averaged sensitive volume. Typically, sensitive volume, of a given search to a given simulated source population, is estimated by drawing signals from the population model and adding them to the detector data as injections. Subsequently injections, which are simulated gravitational waveforms, are searched for by the search pipelines and their signal-to-noise ratio (SNR) is determined. Sensitive volume is estimated, by using Monte-Carlo (MC) integration, from the total number of injections added to the data, the number of injections that cross a chosen threshold on SNR and the astrophysical volume in which the injections are placed. So far, only fixed population models have been used in the estimation of the merger rates. However, as the scope of population analysis broaden in terms of the methodologies and source properties considered, due to an increase in the number of observed GW signals, the procedure will need to be repeated multiple times at a large computational cost. In this letter we address the problem by performing a weighted MC integration. We show how a single set of generic injections can be weighted to estimate the sensitive volume for multiple population models; thereby greatly reducing the computational cost. The weights in this MC integral are the ratios of the output probabilities, determined by the population model and standard cosmology, and the injection probability, determined by the distribution function of the generic injections. Unlike analytical/semi-analytical methods, which usually estimate sensitive volume using single detector sensitivity, the method is accurate within statistical errors, comes at no added cost and requires minimal computational resources.Comment: 11 pages, 1 figur

VAMANA: Modeling Binary Black Hole Population withMinimal Assumptions

We introduce VAMANA, that models the binary black-hole population using a mixture model and facilitates excellent fitting of the model with the data. Flexibility of our modeler results in smaller uncertainties on the posterior distributions and the estimated merger rates allowing extraction of features in the population that may not be visible in parametric methods that model the population using phenomenological models. We present the mass and the spin distribution modeled on the binary black-hole mergers observed during LIGO's and Virgo's first and second observation runs and estimate the binary black-hole merger rate to be $26.6^{+18.2}_ {-13.8}\,\mathrm{Gpc}^{-3}\mathrm{yr}^{-1}$

What's in a binary black hole's mass parameter?

The black hole masses measured from gravitational wave observations appear to cluster around specific mass values. Consequently, the primary~(and chirp) mass distribution of binary black holes inferred using these measurements shows four emerging peaks. These peaks are approximately located at a primary~(chirp) mass value of 10$M_\odot$~(8$M_\odot$), 20$M_\odot$~(14$M_\odot$), 35$M_\odot$~(28$M_\odot$) and 63$M_\odot$~(49$M_\odot$). Although the presence of the first and third peaks has been attributed to binary black hole formation in star clusters or due to the evolution of stellar binaries in isolation, the second peak has received relatively less attention because it lacks significance in the primary mass distribution. In this article, we report that confidence in the second peak depends on the mass parameter we choose to model the population on. Unlike primary mass, this peak is significant when modelled on the chirp mass. We discuss the disparity as a consequence of mass asymmetry in the observations that cluster at the second peak. Finally, we report this asymmetry as part of a potential trend in the mass ratio distribution manifested as a function of the chirp mass, but not as a function of primary mass, when we include the observation GW190814 in our modelling. The chirp mass is not a parameter of astrophysical relevance. Features present in the chirp mass, but not in the primary mass, are relatively difficult to explain and expected to garner significant interest

Constraining black-hole spins with gravitational wave observations

The observation of gravitational-wave signals from merging black-hole binaries enables direct measurement of the properties of the black holes. An individual observation allows measurement of the black-hole masses, but only limited information about either the magnitude or orientation of the black hole spins is available, primarily due to the degeneracy between measurements of spin and binary mass ratio. Using the first six black-hole merger observations, we are able to constrain the distribution of black-hole spins. We perform model selection between a set of models with different spin population models combined with a power-law mass distribution to make inferences about the spin distribution. We assume a fixed power-law mass distribution on the black holes, which is supported by the data and provides a realistic distribution of binary mass-ratio. This allows us to accurately account for selection effects due to variations in the signal amplitude with spin magnitude, and provides an improved inference on the spin distribution. We conclude that the first six LIGO and Virgo observations (Abbott et al. 2016a, 2017a,b,c) disfavour highly spinning black holes against low spins by an odds-ratio of 15:1; thus providing strong constraints on spin magnitudes from gravitational-wave observations. Furthermore, we are able to rule out a population of binaries with completely aligned spins, even when the spins of the individual black holes are low, at an odds ratio of 22,000:1, significantly strengthening earlier evidence against aligned spins (Farr et al. 2017). These results provide important information that will aid in our understanding on the formation processes of black-holes

Reconstruction of Chirp Mass in the Search of Compact Binaries

Excess energy method is used in searches of gravitational waves (GWs) produced from sources with poorly modeled characteristics. It identifies GW events by searching for a coincidence appearance of excess energy in a GW detector network. While it is sensitive to a wide range of signal morphologies, the energy outliers can be populated by background noise events (background), thereby reducing the statistical confidence of a true signal. However, if the physics of the source is partially understood, weak model dependent constraints can be imposed to suppress the background. This letter presents a novel idea of using the reconstructed chirp mass along with two goodness of fit parameters for suppressing background when search is focused on GW produced from the compact binary coalescence

Nonprofessional Phagocytosis Can Facilitate Herpesvirus Entry into Ocular Cells

Phagocytosis is a major mechanism by which the mediators of innate immunity thwart microbial infections. Here we demonstrate that human herpesviruses may have evolved a common mechanism to exploit a phagocytosis-like entrapment to gain entry into ocular cells. While herpes simplex virus-1 (HSV-1) causes corneal keratitis, cytomegalovirus (CMV) is associated with retinitis in immunocompromised individuals. A third herpesvirus, human herpesvirus-8 (HHV-8), is crucial for the pathogenesis of Kaposi's sarcoma, a common AIDS-related tumor of eyelid and conjunctiva. Using laser scanning confocal microscopy, we show that successful infection of ocular cell types by all the three viruses, belonging to three divergent subfamilies of herpesviruses, is facilitated by induction of F-actin rich membrane protrusions. Inhibitors of F-actin polymerization and membrane protrusion formation, cytochalasin D and latrunculin B, were able to block infection by all three viruses. Similar inhibition was seen by blocking phosphoinositide 3 kinase signaling, which is required for microbial phagocytosis. Transmission electron microscopy data using human corneal fibroblasts for HSV-1, human retinal pigment epithelial cells for CMV, and human conjunctival epithelial cells for HHV-8 are consistent with the possibility that pseudopod-like membrane protrusions facilitate virus uptake by the ocular cells. Our findings suggest a novel mechanism by which the nonprofessional mediators of phagocytosis can be infected by human herpesviruses

The Emergence of Structure in the Binary Black Hole Mass Distribution

We use the gravitational wave signals from binary black hole merger events observed by LIGO and Virgo to reconstruct the underlying mass and spin distributions of the population of merging black holes. We reconstruct the population using the mixture model framework VAMANA (Tiwari 2020) using observations in GWTC-2 occurring during the first two observing runs and the first half of the third run (O1, O2, and O3a). Our analysis identifies a structure in the chirp mass distribution of the observed population. Specifically, we identify peaks in the chirp mass distribution at 8, 14, 26, and 45M and a complementary structure in the component mass distribution with an excess of black holes at masses of 9, 16, 30, and 57M. Intriguingly, the location of subsequent peaks are separated by a factor of around two and there is a lack of mergers with chirp masses of 10--12M. We speculate that these features could be footprints of the hierarchical merger scenario. In simplest terms, these features can be explained by a mass-gap near 13M causing black-holes pile-up near the first peak combined with the scenario in which lower mass black-holes hierarchically merge to produce higher mass black-holes. However, if we accept this scenario we have to attribute the existence of a mass gap, lack of cross-generation merger peaks, and lack of high spins in most of the observations to unknown physics. Currently, the results are limited in measurement accuracy due to small numbers of observations, but if confirmed by the aid of future gravitational wave observations these features could have far-reaching implications

Legal Efforts to Curb Child Marriage in India, USA and Australia: A Comparative Analysis

Child marriage is a practice prevalent in many developing as well as developed countries. Despite many legislations and schemes introduced by the respective governments to prevent this immoral practice, it still continues to exist in our society either due to loopholes in the enacted legislations or because society does not accept the laws, giving primacy to their cultural practices or orthodox beliefs. This paper gives a detailed version of child marriage in India by exploring its historical facet, the impact of legislations prevailing and their intelligible conflict with personal laws of various communities. The paper also discusses the laws enacted in the USA and Australia to curb this practice and makes a comparative study regarding the efficiency of these laws

What's in a binary black hole's mass parameter?

The black hole (BH) masses measured from gravitational wave observations appear to cluster around specific mass values. Consequently, the primary (and chirp) mass distribution of binary black holes (BBHs) inferred using these measurements shows four emerging peaks. These peaks are approximately located at a primary (chirp) mass value of 10 (8 ⁠), 20 (14 ⁠), 35 (28 ⁠), and 63 (49 ⁠). Although the presence of the first and third peaks has been attributed to BBH formation in star clusters or due to the evolution of stellar binaries in isolation, the second peak has received relatively less attention because it lacks significance in the primary mass distribution. In this article, we report that confidence in the second peak depends on the mass parameter we choose to model the population on. Unlike primary mass, this peak is significant when modelled on the chirp mass. We discuss the disparity as a consequence of mass asymmetry in the observations that cluster at the second peak. Finally, we report this asymmetry as part of a potential trend in the mass ratio distribution manifested as a function of the chirp mass, but not as a function of primary mass, when we include the observation GW190814 in our modelling. The chirp mass is not a parameter of astrophysical relevance. Features present in the chirp mass, but not in the primary mass, are relatively difficult to explain and expected to garner significant interest