Selected Topics on the Dark Side.

Although significant progress has been made in understanding the nature and history of our universe there are still many open questions in cosmology. The nature of the dark energy (DE) and dark matter (DM) are still elusive. Phantom Cosmology provides an unique opportunity to ``connect'' the phantom driven DE phase to the inflationary era. We present a concrete model where the energy density cycles through several phases. The model predicts transitions from a standard radiation/matter dominated regime to a dark energy/inflationary phases, in a repetitive pattern. An interesting feature of this formalism is that once we include interactions between the ``phantom fluid'' and ordinary matter, the phantom phase naturally gives way to a near exponential inflationary expansion, avoiding the Big Rip singularity. The first phase of stellar evolution in the history of the Universe may be Dark Stars (DS), powered by DM heating. We investigated the properties of DS assuming DM annihilations explain recently found cosmic ray anomalies. Our results show that the final stellar properties, once the star enters the main sequence, are always roughly the same. However the lifetime, final mass, and final luminosity of the DS show moderate dependence on boost factor and concentration parameter. We propose two mechanisms that could explain the growth of Dark Stars to become supermassive (SMDS). The launch of the James Webb Space Telescope (JWST) opens up the possibility of detecting SMDS. Using various dropout redshift selection functions we show that JWST could detect SMDS in a typical deep field survey. Specifically, at z ~ 10 there could be several million SMDS detected as JBand dropouts. The detection of ten-million SMDS is relatively slim at the same z~10. The 1e7 SMDS have a significant chance of being observed as a HBand dropout at z~12, whereas the million-sollarmass SMDS could show up in extremely large numbers (~200) in a typical deep field survey as an F150W dropout. The most promising technique to use in searching for SMDS would be the HBand dropouts. Such an observational discovery would confirm the existence of a new phase of stellar evolution powered by dark matter.Ph.D.PhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/86532/1/cilie_1.pd