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Astrophysics, Cosmology and Extragalactic Astrophysics, astro-ph.CO,General Relativity and Quantum Cosmology, gr-qc
Abstract:
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 [Nat.
Astron. 3, 272 (2019)] 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 $z\gtrsim 2$, and as a tool to cross-check and
cross-validate cosmological EM measurements with complementary GW observations.
