105 research outputs found

    VAMANA: Modeling Binary Black Hole Population withMinimal Assumptions

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    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 26.613.8+18.2Gpc3yr126.6^{+18.2}_ {-13.8}\,\mathrm{Gpc}^{-3}\mathrm{yr}^{-1}

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

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    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 10MM_\odot~(8MM_\odot), 20MM_\odot~(14MM_\odot), 35MM_\odot~(28MM_\odot) and 63MM_\odot~(49MM_\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

    Reconstruction of Chirp Mass in the Search of Compact Binaries

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    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

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    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

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

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    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

    The Emergence of Structure in the Binary Black Hole Mass Distribution

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    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

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

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    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

    Exploring features in the binary black hole population

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    Vamana is a mixture model framework that infers the astrophysical distribution of chirp mass, mass ratio, and spin component aligned with the orbital angular momentum for the binary black holes (BBH) population. We extend the mixing components in this framework to also model the redshift evolution of merger rate and report all the major one- and two-dimensional features in the BBH population using the 69 gravitational-wave signals detected with a false alarm rate <1 yr−1 in the third Gravitational-Wave Transient Catalog (GWTC-3). Endorsing our previous report and a recent corroborating report from LIGO Scientific, Virgo, and KAGRA Collaborations, we observe the chirp mass distribution has multiple peaks and a lack of mergers with chirp masses 10–12 M⊙. In addition, we observe that aligned spins show mass dependence with heavier binaries exhibiting larger spins, the mass ratio shows a dependence on the chirp mass but not on the aligned spin, and the redshift evolution of the merger rate for the peaks in the mass distribution is disparate. These features possibly reflect the astrophysics associated with the BBH formation channels. However, additional observations are needed to improve our limited confidence in them
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