arXiv subjects

Kristen Schumacher

Publications and source records attributed to Kristen Schumacher.

5 recordsLinked to original sources

arXiv2026

The Stochastic Siren: Astrophysical Gravitational-Wave Background Measurements of the Hubble Constant

We report the first measurement of the Hubble constant $H_0$ using the stochastic gravitational-wave background arising from binary black hole mergers. This astrophysical background is sensitive to the expansion history of the Universe and thus can be used for cosmological parameter inference independently of not only electromagnetic methods, but also gravitational-wave standard siren approaches. We describe the background's cosmological dependence and show how it can be used as a ``stochastic siren'' to measure $H_0$. By analyzing existing resolved binary black hole mergers and the current non-detection of the background, we find that $H_0$ can be measured more accurately relative to using resolved mergers alone. We also note that the stochastic siren may serve a unique role in the Hubble tension in that the lower bound of the $H_0$ measurement would progressively increase with continued non-detection of the background.

astro-ph.CO↗

arXiv2025

Better early than never: A new test for superluminal gravitational wave polarizations

In some beyond-Einstein theories of gravity, gravitational waves can contain up to six polarizations, which are allowed to propagate at different speeds faster than light. These different propagation speeds imply that polarizations generated by the same source will not arrive simultaneously at the detector. Current constraints on the speed of propagation of transverse-traceless polarizations, however, indicate that any additional polarizations must arrive with or before the transverse-traceless ones. We propose a new technique to test for the existence of superluminal, non-transverse-traceless polarizations that arrive in the data before a gravitational-wave observation of transverse-traceless modes. We discuss the circumstances in which these non-transverse-traceless polarizations would be detectable and what constraints could be placed if they are not detected. To determine whether this new test of general relativity with gravitational wave observations is practical, we outline and address many of the challenges it might face. Our arguments lead us to conclude that this new test is not only physically well-motivated but also feasible with current detectors.

gr-qc↗

arXiv2023

Gravitational wave constraints on Einstein-æther theory with LIGO/Virgo data

Lorentz symmetry is a fundamental property of Einstein's theory of general relativity that one may wish to test with gravitational wave observations. Einstein-aether theory is a model that introduces Lorentz-symmetry breaking in the gravitational sector through an aether vector field, while still leading to second-order field equations. This well-posed theory passes particle physics constraints because it modifies directly only the gravitational sector, yet it predicts deviations in the inspiral and coalescence of compact objects. We here, for the first time, put this theory to the test by comparing its gravitational wave predictions directly against LIGO/Virgo gravitational wave data. We construct a waveform model for Einstein-aether theory, EA_IMRPhenomD_NRT, through modifications of the general relativity IMRPhenomD_NRTidalv2 model (used by the LIGO/VIRGO collaboration). This model constructs a reponse function that not only contains the transverse-traceless polarization, but also additional Einstein-aether (scalar and vectorial) polarizations simultaneously. We then use the many current constraints on the theory to construct non-trivial priors for the Einstein-aether coupling constants. After testing the waveform model, we conduct parameter estimation studies on two gravitational wave events: GW170817 and GW190425. We find that these data are not sufficiently informative to place constraints on the theory that are stronger than current bounds from binary pulsar, solar system and cosmological observations. This is because, although Einstein-aether modifications include additional polarizations and have been computed beyond leading post-Newtonian order, these modifications are dominated by (already-constrained) dipole effects. These difficulties make it unclear whether future gravitational wave observations will be able to improve on current constraints on Einstein-aether theory.

gr-qc↗

arXiv2023

Gravitational wave polarizations with different propagation speeds

In some modified theories of gravity, gravitational waves can contain up to six different polarizations, which can travel at speeds different from that of light. Searches for these different polarizations in gravitational wave data are important because any detection would be clear evidence of new physics, while clear non-detections could constrain some modified theories. The first step toward searching the data for such gravitational wave content is the calculation of the amplitudes of these different polarizations. Here we present a model-independent method to obtain the different polarizations of gravitational waves directly from the metric perturbation in theories where these polarizations are allowed to travel at different speeds. We develop our calculations so that the same procedure works with either the metric perturbation itself or its trace-reversed form. Our results are in agreement with previous work in the limit that all polarization speeds are the speed of light. We demonstrate how our model-independent method can be used with two specific modified theories of gravity, suggesting its wide applicability to other theories that allow for different gravitational wave propagation speeds. We further extend the parametrized post-Einsteinian formalism to apply to such theories that travel with different speeds. Finally, we discuss how the different speeds of different polarizations may affect null stream tests of general relativity with gravitational wave observations by multiple interferometers. Differences in propagation speeds may make null streams ineffective or lead to the detection of what seem to be isolated scalar or vector modes.

gr-qc↗

arXiv2020

Measuring Nuclear Matter Parameters with NICER and LIGO/Virgo

The NICER Collaboration recently reported the measurement of the mass and radius of a pulsar PSR J0030+0451. We here use this new measurement to constrain one of the higher-order nuclear matter parameters $K_{\mathrm{sym,0}}$. We further combine the tidal measurement of the binary neutron star merger GW170817 by LIGO/Virgo to derive a joint 1-$σ$ constraint as $K_{\mathrm{sym,0}} = -102^{+71}_{-72}$ MeV. We believe this is the most reliable bound on the parameter to date under the assumption that there is no new physics above the saturation density which impacts neutron star observations.

astro-ph.HE↗