Abstract
ABSTRACTThe Laser Interferometer Space Antenna (LISA) will open the mHz frequency window of the gravitational-wave (GW) landscape. Among all the new GW sources expected to emit in this frequency band, extreme mass-ratio inspirals (EMRIs) constitute a unique laboratory for astrophysics and fundamental physics. Here, we show that EMRIs can also be used to extract relevant cosmological information, complementary to both electromagnetic (EM) and other GW observations. By using the loudest EMRIs (S/N > 100) detected by LISA as dark standard sirens, statistically matching their sky localization region with mock galaxy catalogues, we find that constraints on H0 can reach ∼1.1 per cent (∼3.6 per cent) accuracy, at the 90 per cent credible level, in our best(worst)- case scenario. By considering a dynamical dark energy (DE) cosmological model, with ΛCDM parameters fixed by other observations, we further show that in our best(worst)- case scenario ∼5.9 per cent (∼12.3 per cent) relative uncertainties at the 90 per cent credible level can be obtained on w0, the DE equation of state parameter. Besides being relevant in their own right, EMRI measurements will be affected by different systematics compared to both EM and ground-based GW observations. Cross-validation with complementary cosmological measurements will therefore be of paramount importance, especially if convincing evidence of physics beyond ΛCDM emerges from future observations.
Highlights
The first direct detection of gravitational waves (GWs) in 2015 (Abbott et al 2016a) ended a long experimental quest and opened a new observational window onto the Universe
By using the loudest extreme mass-ratio inspirals (EMRIs) (SNR>100) detected by Laser Interferometer Space Antenna (LISA) as dark standard sirens, statistically matching their sky localisation region with mock galaxy catalogs, we find that constraints on H0 can reach ∼1.1% (∼3.6%) accuracy, at the 90% credible level, in our best case scenario
As expected, our results obtained with M1 are superseded by those obtained with M6, as in this case the total number of useful EMRIs is more than doubled
Summary
The first direct detection of gravitational waves (GWs) in 2015 (Abbott et al 2016a) ended a long experimental quest and opened a new observational window onto the Universe. The simultaneous measurement of both the luminosity distance (from the GW waveform) and the redshift (from EM observations) of a GW source provides data points to fit the so-called distance-redshift relation (Peebles 1993; Weinberg 2008), which links the luminosity distance to the redshift of each point in the Universe and is a function of the cosmological parameters characterizing the cosmic background expansion. At low redshift this relation becomes the Hubble law, that only depends on the Hubble constant H0. Future observations of similar events will reduce the uncertainty on H0 (Dalal et al 2006; Nissanke et al 2013; Chen et al 2018), and possibly will help solving the tension on its measured value between local and CMB observations (e.g. Ade et al (2016); Aghanim et al (2018); Riess et al (2016, 2019); Mörtsell & Dhawan (2018); Feeney et al (2019))
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