Description
I will present a formalism to characterize the imprints of post-recombination fluctuation sources.
I will consider a sequestered dark sector interacting only gravitationally with the Standard Model
and dark matter. For dynamics on timescales much shorter than the Hubble time, stress-tensor
conservation restricts the source to continuous contributions and instantaneous injections of pressure
and anisotropic stress. The latter dominates the integrated Sachs–Wolfe signal, enabling strong
constraints on such sources from the Cosmic Microwave Background. As an example, I will bound the
allowed dark-sector energy density for late first-order phase transitions. If times permits I will also discuss extension
of this framework before recombination.