In $Lambda$CDM cosmology, structure formation is halted shortly after dark energy dominates the mass/energy budget of the Universe. A manifestation of this effect is that in such a cosmology the turnaround radius has an upper bound. Recently, a new,
local, test for the existence of dark energy in the form of a cosmological constant was proposed based on this turnaround bound. Before designing an experiment that, through high-precision determination of masses and turnaround radii, will challenge $Lambda$CDM cosmology, we have to answer two important questions: first, when turnaround-scale structures are predicted to be close enough to their maximum size, so that a possible violation of the bound may be observable. Second, which is the best mass scale to target for possible violations of the bound. Using the Press-Schechter formalism, we find that turnaround structures have in practice already stopped forming, and consequently, the turnaround radius of structures must be very close to the maximum value today. We also find that the mass scale of $sim 10^{13} M_odot$ characterizes turnaround structures that start to form in a statistically important number density today. This mass scale also separates turnaround structures with different cosmological evolution: smaller structures are no longer readjusting their mass distribution inside the turnaround scale, they asymptotically approach their ultimate abundance from higher values, and they are common enough to have, at some epoch, experienced major mergers with structures of comparable mass; larger structures exhibit the opposite behavior. We call this mass scale the transitional mass scale and we argue that it is the optimal for the purpose outlined above. As a corollary result, we explain the different accretion behavior of small and larger structures observed in already conducted numerical simulations.
Recent Planck results have shown that radiation from the cosmic microwave background passes through foregrounds in which aligned dust grains produce polarized dust emission, even in regions of the sky with the lowest level of dust emission. One of th
e most commonly used ways to remove the dust foreground is to extrapolate the polarized dust emission signal from frequencies where it dominates (e.g., ~ 350 GHz) to frequencies commonly targeted by cosmic microwave background experiments (e.g., ~150 GHz). In this paper, we describe an interstellar medium effect that can lead to decorrelation of the dust emission polarization pattern between different frequencies due to multiple contributions along the line of sight. Using a simple 2-cloud model we show that there are two conditions under which this decorrelation can be large: (a) the ratio of polarized intensities between the two clouds changes between the two frequencies; (b) the magnetic fields between the two clouds contributing along a line of sight are significantly misaligned. In such cases, the 350 GHz polarized sky map is not predictive of that at 150 GHz. We propose a possible correction for this effect, using information from optopolarimetric surveys of dichroicly absorbed starlight.
