Speaker
Description
I will discuss cosmological domain walls with a review of their
evolution and how they produce gravitational waves. Particular
attention will be devoted to melting domain walls which are described
by tension red-shifting with the expansion of the Universe, so that
this network eventually fades away completely. These melting domain
walls emit gravitational waves with the low-frequency spectral shape
favoured by the recent NANOGrav 15 yrs data. This scenario involves a
feebly coupled scalar field, which can serve as a promising dark
matter candidate. This ultra-light dark matter has mass below 0.01 neV
which is accessible through planned observations thanks to the effects
of superradiance of rotating black holes. This talk is based on recent
works: arXiv:2104.13722, arXiv:2112.12608, arXiv:2307.04582 and
arXiv: 2406.17053.
