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Cosmography with bright and Love sirens

Arnab DhaniSsohrab BorhanianAnuradha GuptaBangalore Sathyaprakash
Dec 2022
Precision cosmology is crucial to understand the different energy componentsin the Universe and their evolution through cosmic time. Gravitational wavesources are standard sirens that can accurately map out distances in theUniverse. Together with the source redshift information, we can then probe theexpansion history of the Universe. We explore the capabilities of variousgravitational-wave detector networks to constrain different cosmological modelswhile employing separate waveform models for inspiral and post-merger part ofthe gravitational wave signal from equal mass binary neutron stars. We considertwo different avenues to measure the redshift of a gravitational-wave source:first, we examine an electromagnetic measurement of the redshift via either akilonova or a gamma ray burst detection following a binary neutron star merger(the electromagnetic counterpart method); second, we estimate the redshift fromthe gravitational-wave signal itself from the adiabatic tides between thecomponent stars characterized by the tidal Love number, to provide a secondmass-scale and break the mass-redshift degeneracy (the counterpart-lessmethod). We find that the electromagnetic counterpart method is better suitedto measure the Hubble constant while the counterpart-less method places morestringent bounds on other cosmological parameters. In the era ofnext-generation gravitational-wave detector networks, both methods achievesub-percent measurement of the Hubble constant $H_0$ after one year ofobservations. The dark matter energy density parameter $\Omega_{\rm M}$ in the$\Lambda$CDM model can be measured at percent-level precision using thecounterpart method, whereas the counterpart-less method achieves sub-percentprecision. We, however, do not find the postmerger signal to contributesignificantly to these precision measurements.