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Full-Text Articles in Physical Sciences and Mathematics
Dark-Energy Evolution Across The Cosmological-Constant Boundary, Robert R. Caldwell, Michael Doran
Dark-Energy Evolution Across The Cosmological-Constant Boundary, Robert R. Caldwell, Michael Doran
Dartmouth Scholarship
We explore the properties of dark-energy models for which the equation of state, w, defined as the ratio of pressure to energy density, crosses the cosmological-constant boundary w=−1. We adopt an empirical approach, treating the dark energy as an uncoupled fluid or a generalized scalar field. We describe the requirements for a viable model, in terms of the equation of state and sound speed. A generalized scalar field cannot safely traverse w=−1, although a pair of scalars with w>−1 and w<−1 will work. A fluid description with a well-defined sound speed can also cross the boundary. Contrary to expectations, such a crossing model does not instantaneously resemble a cosmological constant at the moment w=−1 since the density and pressure perturbations do not necessarily vanish. But because a dark energy with w<−1 dominates only at very late times, and because the dark energy is not generally prone to gravitational clustering, then crossing the cosmological-constant boundary leaves no distinct imprint.
Cosmic Shear Of The Microwave Background: The Curl Diagnostic, Asantha Cooray, Marc Kamionkowski, Robert R. Caldwell
Cosmic Shear Of The Microwave Background: The Curl Diagnostic, Asantha Cooray, Marc Kamionkowski, Robert R. Caldwell
Dartmouth Scholarship
Weak-lensing distortions of the cosmic-microwave-background (CMB) temperature and polarization patterns can reveal important clues to the intervening large-scale structure. The effect of lensing is to deflect the primary temperature and polarization signal to slightly different locations on the sky. Deflections due to density fluctuations, gradient-type for the gradient of the projected gravitational potential, give a direct measure of the mass distribution. Curl-type deflections can be induced by, for example, a primordial background of gravitational waves from inflation or by second-order effects related to lensing by density perturbations. Whereas gradient-type deflections are expected to dominate, we show that curl-type deflections can …