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We show that future observations of binary neutron star systems with electromagnetic counterparts together with the traditional probes of low- and high-redshift Type Ia supernovae (SNe Ia) can help resolve the Hubble tension. The luminosity distance inferred from these probes and its scatter depend on the underlying cosmology. By using the gravitational lensing of light or gravitational waves emitted by, and peculiar motion of, these systems we derive constraints on the sum of neutrino masses, the equation of state of dark energy parametrized in the form $w_0 + w_a (1-a)$, along with the Hubble constant and cold dark matter density in the universe. We show that even after marginalizing over poorly constrained physical quantities, such as the sum of neutrino masses and the nature of dark energy, low-redshift gravitational-wave observations, in combination with SNe Ia, have the potential to rule out new physics as the underlying cause of the Hubble tension at $gtrsim 5.5sigma$.
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Gravitational waves detected from well-localized inspiraling binaries would allow to determine, directly and independently, both binary luminosity and redshift. In this case, such systems could behave as standard candles providing an excellent probe of cosmic distances up to $z <0.1$ and thus complementing other indicators of cosmological distance ladder.
Gravitational waves (GWs) directly measure the luminosity distance to the merger, which, when combined with an independent measurement of the sources redshift, provides a novel probe of cosmology. The proposed next generation of ground-based GW detectors, Einstein Telescope and Cosmic Explorer, will detect tens of thousands of binary neutron stars (BNSs) out to cosmological distances ($z>2$), beyond the peak of the star formation rate (SFR), or cosmic noon. At these distances, it will be challenging to measure the sources redshifts by observing electromagnetic (EM) counterparts or statistically marginalizing over a galaxy catalog. In the absence of an EM counterpart or galaxy catalog, Ding et al. showed that theoretical priors on the merger redshift distribution can be used to infer parameters in a $w$CDM cosmology. We argue that in the BNS case, the redshift distribution will be measured by independent observations of short gamma ray bursts (GRBs), kilonovae, and known BNS host galaxies. We show that, in addition to measuring the background cosmology, this method can constrain the effects of dark energy on modified GW propagation. We consider the simple case in which the BNS rate is textit{a priori} known to follow the SFR. If the SFR is perfectly known, $mathcal{O}(10,000)$ events (to be expected within a year of observation with Cosmic Explorer) would yield a sub-tenth percent measurement of the combination $H_0^{2.8}Omega_M$. Fixing $H_0$ and $Omega_M$, this method may enable a 5% measurement of the dark energy equation of state parameter. Fixing the background cosmology and probing modified GW propagation, the running of the Planck mass parameter $c_M$ may be measured to $pm0.02$. Although realistically, the redshift evolution of the merger rate will be uncertain, prior knowledge of the peak redshift will provide valuable information for standard siren analyses.
The purpose of this work is to investigate the prospects of using the future standard siren data without redshift measurements to constrain cosmological parameters. With successful detections of gravitational wave (GW) signals an era of GW astronomy has begun. Unlike the electromagnetic domain, GW signals allow direct measurements of luminosity distances to the sources, while their redshifts remain to be measured by identifying electromagnetic counterparts. This leads to significant technical problems for almost all possible BH-BH systems. It is the major obstacle to cosmological applications of GW standard sirens. In this paper, we introduce the general framework of using luminosity distances alone for cosmological inference. The idea is to use the prior knowledge of the redshift probability distribution for coalescing sources from the intrinsic merger rates assessed with population synthesis codes. Then the posterior probability distributions for cosmological parameters can be calculated. We demonstrate the performance of our method on the simulated mock data and show that the luminosity distance measurement would enable an accurate determination of cosmological parameters up to $20%$ uncertainty level. We also find that in order to infer $H_0$ to 1% level with flat $Lambda$CDM model, we need about $10^5$ events.
An interesting test on the nature of the Universe is to measure the global spatial curvature of the metric in a model independent way, at a level of $|Omega_k|<10^{-4}$, or, if possible, at the cosmic variance level of the amplitude of the CMB fluctuations $|Omega_k|approx10^{-5}$. A limit of $|Omega_k|<10^{-4}$ would yield stringent tests on several models of inflation. Further, improving the constraint by an order of magnitude would help in reducing model confusion in standard parameter estimation. Moreover, if the curvature is measured to be at the value of the amplitude of the CMB fluctuations, it would offer a powerful test on the inflationary paradigm and would indicate that our Universe must be significantly larger than the current horizon. On the contrary, in the context of standard inflation, measuring a value above CMB fluctuations will lead us to conclude that the Universe is not much larger than the current observed horizon, this can also be interpreted as the presence of large fluctuations outside the horizon. However, it has proven difficult, so far, to find observables that can achieve such level of accuracy, and, most of all, be model-independent. Here we propose a method that can in principle achieve that, this is done by making minimal assumptions and using distance probes that are cosmology-independent: gravitational waves, redshift drift and cosmic chronometers. We discuss what kind of observations are needed in principle to achieve the desired accuracy.
Quasars have recently been used as an absolute distance indicator, extending the Hubble diagram to high redshift to reveal a deviation from the expansion history predicted for the standard, $Lambda$CDM cosmology. Here we show that the Laser Interferometer Space Antenna (LISA) will efficiently test this claim with standard sirens at high redshift, defined by the coincident gravitational wave (GW) and electromagnetic (EM) observations of the merger of massive black hole binaries (MBHBs). Assuming a fiducial $Lambda$CDM cosmology for generating mock standard siren datasets, the evidence for the $Lambda$CDM model with respect to an alternative model inferred from quasar data is investigated. By simulating many realizations of possible future LISA observations, we find that for $50%$ of these realizations (median result) 4 MBHB standard siren measurements will suffice to strongly differentiate between the two models, while 14 standard sirens will yield a similar result in $95%$ of the realizations. In addition, we investigate the measurement precision of cosmological parameters as a function of the number of observed LISA MBHB standard sirens, finding that 15 events will on average achieve a relative precision of 5% for $H_0$, reducing to 3% and 2% with 25 and 40 events, respectively. Our investigation clearly highlights the potential of LISA as a cosmological probe able to accurately map the expansion of the universe at $zgtrsim 2$, and as a tool to cross-check and cross-validate cosmological EM measurements with complementary GW observations.
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