Gravitational waves from the early universe

Understand

Even though different models could already be constrained using CMB data, these models remained unconstrained at higher frequency scales, and, therefore, the knowledge of new physics at these scales remained limited, relying on theoretical assumptions and extrapolations.

• Recently, however, we experienced the advent of gravitational-wave and multi-messenger astronomy, including the outstanding detections by the LIGO-Virgo collaboration and the searches for Hellings-Downs correlations in pulsar timing data.
• Over the next decades, ongoing and future collaborations will explore different frequency ranges of the gravitational wave spectrum, granting access to regimes inaccessible by the CMB and collider experiments.
• These include ground-based, space-borne, and pulsar timing array searches for gravitational waves.