Search for gravitational-lensing signatures in the full third observing run of the LIGO-Virgo network

Gravitational lensing by massive objects along the line of sight to the source causes distortions of gravitational wave-signals; such distortions may reveal information about fundamental physics, cosmology and astrophysics. In this work, we have extended the search for lensing signatures to all binary black hole events from the third observing run of the LIGO--Virgo network. We search for repeated signals from strong lensing by 1) performing targeted searches for subthreshold signals, 2) calculating the degree of overlap amongst the intrinsic parameters and sky location of pairs of signals, 3) comparing the similarities of the spectrograms amongst pairs of signals, and 4) performing dual-signal Bayesian analysis that takes into account selection effects and astrophysical knowledge. We also search for distortions to the gravitational waveform caused by 1) frequency-independent phase shifts in strongly lensed images, and 2) frequency-dependent modulation of the amplitude and phase due to point masses. None of these searches yields significant evidence for lensing. Finally, we use the non-detection of gravitational-wave lensing to constrain the lensing rate based on the latest merger-rate estimates and the fraction of dark matter composed of compact objects

Ultralight vector dark matter search using data from the KAGRA O3GK run

Among the various candidates for dark matter (DM), ultralight vector DM can be probed by laser interferometric gravitational wave detectors through the measurement of oscillating length changes in the arm cavities. In this context, KAGRA has a unique feature due to differing compositions of its mirrors, enhancing the signal of vector DM in the length change in the auxiliary channels. Here we present the result of a search for U(1)B−L gauge boson DM using the KAGRA data from auxiliary length channels during the first joint observation run together with GEO600. By applying our search pipeline, which takes into account the stochastic nature of ultralight DM, upper bounds on the coupling strength between the U(1)B−L gauge boson and ordinary matter are obtained for a range of DM masses. While our constraints are less stringent than those derived from previous experiments, this study demonstrates the applicability of our method to the lower-mass vector DM search, which is made difficult in this measurement by the short observation time compared to the auto-correlation time scale of DM

The Effect Of Director Monitoring On Bid And Ask Spreads

We examine whether the market assesses a lower level of information asymmetry to firms that are perceived to be monitored more intensely by members of the board of directors. We use changes in bid-ask spreads as proxies for changes in information asymmetry between the firm and the market around the time earnings are announced. Our study is innovative in its association of director monitoring with levels of information asymmetry as reflected in quoted spreads. Our sample includes 145 firms included in the Toronto Stock Exchange 300 Index (TSX-300). The TSX\u27s hybrid market structure provides a unique international setting in which to examine the effects of governance on information asymmetry. Results indicate that the market attributes a lower level of information asymmetry to firms with a larger proportion of outside directors on the board. Contrary to our predictions, we find the larger the proportion of voting rights held by directors, the higher the level of information asymmetry attributed to the firm. We provide some evidence that a separate CEO/Chair leadership structure is associated with reduced information asymmetry. From a practice perspective, we are able to provide some preliminary insight into the potential value attributed by market participants to the imposition of regulation surrounding certain director monitoring activities