The Milky Way did not form in isolation, but is the product of a complex evolution of generations of mergers, collapses, star formation, supernovae and collisional heating, radiative and collisional cooling, and ejected nucleosynthesis. Moreover, all of this occurs in the context of the cosmic expansion, the formation of cosmic laments, dark-matter haloes, spiral density waves, and emerging dark energy. This paper summarizes a review of recent attempts to reconstruct this complex evolution. We compare simulated properties with various observed properties of the Local Group. Among the generic features of simulated systems is the tendency for galactic halos to form within the dark matter filaments that define a super- galactic plane. Gravitational interaction along this structure leads to a streaming ow toward the two dominant galaxies in the cluster. We analyze this alignment and streaming flow and compare with the observed properties of Local-Group galaxies. Our comparison with Local Group properties suggests that some dwarf galaxies in the Local Group are part of a local streaming ow. These simulations also suggest that a significant fraction of the Galactic halo formed at large distances and arrived later along these streaming ows.

We consider a late decaying dark matter model in which cold dark matter begins to decay into relativistic particles at a recent epoch (z ≤ 1). A complete set of Boltzmann equations for dark matter and other relevant particles particles is derived, which is necessary to calculate the evolution of the energy density and density perturbations. We show that the large entropy production and associated bulk viscosity from such decays leads to a recently accelerating cosmology consistent with observations. We determine the constraints on the decaying dark matter model with bulk viscosity by using a MCMC method combined with observational data of the CMB and type Ia supernovae.

If the present universe is slightly open then pre-in ation curvature would appear as a cosmic dark-flow component of the CMB dipole moment. We summarize current cosmological constraints on this cosmic dark ow and analyze the possible constraints on parameters characterizing the pre-in ating universe in an in ation model with a present-day very slightly open ΛCDM cosmology. We employ an analytic model to show that for a broad class of in ation-generating effective potentials, the simple requirement that the observed dipole moment represents the pre-in ation curvature as it enters the horizon allows one to set upper and lower limits on the magnitude and wavelength scale of pre-in ation uctuations in the in aton field and the curvature parameter of the pre-in ation universe, as a function of the fraction of the total initial energy density in the in aton field. We estimate that if the current CMB dipole is a universal dark flow (or if it is near the upper limit set by the Planck Collaboration) then the present constraints on ΛCDM cosmological parameters imply rather small curvature Ωk ~ 0:1 for the pre-in ating universe for a broad range of the fraction of the total energy in the in aton field at the onset of in ation. Such small pre-in ation curvature might be indicative of open-in ation models in which there are two epochs of in ation.