Improved constraint on the primordial gravitational-wave density using recent cosmological data and its impact on cosmic string models

Understand

The production of a primordial stochastic gravitational-wave background by processes occuring in the early Universe is expected in a broad range of models.

• Observing this background would open a unique window onto the Universe's evolutionary history.
• Probes like the Cosmic Microwave Background (CMB) or the Baryon Acoustic Oscillations (BAO) can be used to set upper limits on the stochastic gravitational-wave background energy density $\Omega_{GW}$ for frequencies above $10^{-15}$ Hz.
• We perform a profile likelihood analysis of the Planck CMB temperature anisotropies and gravitational lensing data combined with WMAP low-$\ell$ polarization, BAO, South Pole Telescope and Atacama Cosmology Telescope data.