arXiv subjects

C. Karathanasis

Publications and source records attributed to C. Karathanasis.

6 recordsLinked to original sources

arXiv2022

An instrumented baffle for the Advanced Virgo Input Mode Cleaner End Mirror

A novel instrumented baffle surrounding the suspended end mirror in the input mode cleaner cavity of the Virgo interferometer was installed in spring 2021. Since then, the device has been regularly operated in the experiment and the obtained results indicate a good agreement with simulations of the stray light inside the optical cavity. The baffle will operate in the upcoming O4 observation run, serving as a demonstrator of the technology designed to instrument the baffles in front of the main mirrors in time for O5. In this paper we present a detailed description of the baffle design, including mechanics, front-end electronics, data acquisition, as well as optical and vacuum tests, calibration and installation procedures, and performance results.

physics.ins-det↗

arXiv2022

Cosmology in the dark: How compact binaries formation impact the gravitational-waves cosmological measurements

Information about the mass spectrum of compact stars can be used to infer cosmological parameters from gravitational waves (GW) in the absence of redshift measurements obtained from electromagnetic (EM) observations. This method will be fundamental in measuring and testing cosmology with GWs for current and future ground-based GW detectors where the majority part of sources are detected without an associated EM counterpart. In this proceeding, we will discuss the prospects and limitations of this approach for studying cosmology. We will show that, even when assuming GW detectors with current sensitivities, the determination of the Hubble constant is strongly degenerate with the maximum mass for black hole production. We will discuss how assuming wrong models for the underlying population of black hole events can bias the Hubble constant estimate up to 40\%.

gr-qc↗

arXiv2021

Measurement of the Stray Light in the Advanced Virgo Input Mode Cleaner Cavity using an instrumented baffle

A new instrumented baffle was installed in Spring 2021 at Virgo surrounding the suspended mirror in the input mode cleaner triangular cavity. It serves as a demonstrator of the technology designed to instrument the baffles in the main arms in the near future. We present, for the first time, results on the measured scattered light distribution inside the cavity as determined by the new device using data collected between May and July 2021, with Virgo in commissioning phase and operating with an input laser power in the cavity of 28.5~W. The sensitivity of the baffle is discussed and the data is compared to scattered light simulations.

astro-ph.IM↗

arXiv2021

Cosmology in the dark: On the importance of source population models for gravitational-wave cosmology

Knowledge of the shape of the mass spectrum of compact objects can be used to help break the degeneracy between the mass and redshift of the gravitational wave (GW) sources, and thus can be used to infer cosmological parameters in the absence of redshift measurements obtained from electromagnetic observations. In this paper, we study extensively different aspects of this approach, including its computational limits and achievable accuracy. We focus on ground-based detectors with current and future sensitivities, we first perform the analysis of an extensive set of simulated data with a hierarchical Bayesian scheme inferring population and cosmological parameters. We consider a population model (power-law plus Gaussian) which exhibits characteristic scales (extremes of the mass spectrum, presence of an accumulation point) that allows an indirect estimate of the source redshift. Our analysis of this catalog highlights and quantifies the tight interplay between source population and cosmological parameters, as well as the influence of initial assumptions (whether formulated on the source or cosmological parameters). We then validate our results by an "end-to-end" analysis using simulated GW data and posterior samples generated from Bayesian samplers used for GW parameter estimation, thus mirroring the analysis chain used for observational data for the first time in literature. Our results then lead us to re-examine the estimation of $H_0$ obtained with GWTC-1, and we show explicitly how population assumptions impact the final $H_0$ result. Our results underline the importance of inferring population and cosmological parameters jointly (and not separately as is often assumed). The only exception, as we discuss, is if an electromagnetic counterpart was to be observed for all the BBH events: then the population assumptions have less impact on the estimation of cosmological parameters.

gr-qc↗

arXiv2021

Bayesian inference for compact binary coalescences with BILBY: Validation and application to the first LIGO--Virgo gravitational-wave transient catalogue

Gravitational waves provide a unique tool for observational astronomy. While the first LIGO--Virgo catalogue of gravitational-wave transients (GWTC-1) contains eleven signals from black hole and neutron star binaries, the number of observations is increasing rapidly as detector sensitivity improves. To extract information from the observed signals, it is imperative to have fast, flexible, and scalable inference techniques. In a previous paper, we introduced BILBY: a modular and user-friendly Bayesian inference library adapted to address the needs of gravitational-wave inference. In this work, we demonstrate that BILBY produces reliable results for simulated gravitational-wave signals from compact binary mergers, and verify that it accurately reproduces results reported for the eleven GWTC-1 signals. Additionally, we provide configuration and output files for all analyses to allow for easy reproduction, modification, and future use. This work establishes that BILBY is primed and ready to analyse the rapidly growing population of compact binary coalescence gravitational-wave signals.

astro-ph.IM↗

arXiv2020

Gravitational wave friction in light of GW170817 and GW190521

We use the gravitational wave (GW) events GW170817 and GW190521, together with their proposed electromagnetic counterparts, to constrain cosmological parameters and theories of gravity beyond General Relativity (GR). In particular we consider models with a time-varying Planck mass, large extra-dimensions, and a phenomenological parametrization covering several beyond-GR theories. In all three cases, this introduces a friction term into the GW propagation equation, effectively modifying the GW luminosity distance. We set constraints on $Λ$CDM parameters and GR deviation parameters using two sets of priors on the Hubble constant and matter energy density. With priors set to the measured Planck's mission values, we find that with the inclusion of GW190521, the two GR deviation parameters constraints improves by a factor $\sim 10$, we report a number of spacetime dimensions compatible with $4$ with an precision of $2.5\%$ (at 95\% CL) and an upper limit to the variation of Netwon's constant at the epoch of GW170817 $<20\%$. With wide priors on the Hubble constant and matter energy density, we show that it is still possible to constrain the $Λ$CDM parameters and GR deviation parameters conjointly from GW170817 and GW190521 obtaining constraints on GR deviation parameters which are a factor $2-6$ worse than the results using restricted priors on $Λ$CDM parameters.

gr-qc↗