On the inference of cosmological parameters with gravitational waves

Abstract

Gravitational waves provide an alternative route to determine the values of cosmological parameters. Similarly to electromagnetic observations, cosmological inference canproceed in different ways. A late-time or local approach attempts
to reconstruct the history of the Universe using measurements in the nearby Universe. The analogues of supernova standard candles in gravitational-wave astronomy are compact binary coalescences, which act as standard sirens. In addition to individual sources, we also expect a stochastic background of gravitational waves from unresolved astrophysical sources, whose spectral shape encodes information about the source population and, indirectly, about cosmology. For the early-Universe case, we may instead observe a cosmological (primordial) stochastic background of gravitational waves, which would allow us, in principle, to probe new physics at energies much closer to the Big Bang than those accessible through electromagnetic observations. While the local approach is already possible with current and future ground-based detectors, the observability of a primordial stochastic background remains uncertain, both for experimental and theoretical reasons.
In this talk I will review gravitational waves as cosmological probes, their complementarity with traditional probes, and discuss some of their intrinsic challenges. I will present the case of individual sources as well as that of stochastic backgrounds.
Finally, I will discuss recent results from current observations and advances in the search for and characterisation of stochastic gravitational-wave backgrounds.