Throwing pebbles in the primordial pond

We consider anisotropies in the Cosmic Microwave Background (CMB) generated by spatially limited seeds; these objects could correspond to relics of high energy symmetry breaking in the early universe. It is shown how the CMB perturbation propagate beyond the size of the seed in the form of waves traveling with the CMB sound velocity. Moreover, these waves are the substantial part of the signal, both for polarization and temperature. The explanation of this phenomenology in terms of the CMB equations is given. Observationally, this effect is threefold promising. First, it enlarges the signal from a seed intersecting the last scattering surface to the scale of the CMB sound horizon at decoupling, that is roughly one degree in the sky. Second, it offers cross correlation possibilities between the polarization and temperature signals. Third, it allows to unambiguously distinguish these structures from point-like astrophysical sources.