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What can be the cause of the accelerated expansion of the Universe? Currently, there are only two contenders, dark energy or modified gravity at very large distances. As part of this project we will study both possibilities.

Dark Energy: A dark energy possessing a peculiar equation of state (EOS) with w < 0. The cosmological constant, Lambda, is the simplest case, w=-1. Quantum field theories -- the basis of all of our understanding of the physical world -- predict a vacuum energy which acts like a nonzero cosmological constant. However, Lambda as observed is ~60 - 120 orders of magnitude smaller than predicted, by far the largest such discrepancy in all of science.

Modified Gravity: Our current models of cosmology rest on the success of general relativity. Nevertheless, the theory may well fail at the enormous distances relevant to the dark energy problem. Here, too, absolutely new ideas are required to present viable alternatives to the status quo. Any alternative theory must not only reproduce the successes of relativity, but also make new predictions that can be observationally tested.

Publications
  1. Mapping the Dark Kinetics S. Bashinsky, ApJ, submitted arXiv:0707.0692
  2. Perturbations of Dark Sectors from the CMB,
    S. Bashinsky, to appear in the Proceedings of the 11th Marcel Grossmann Meeting
  3. Direct Reconstruction of the Dark Energy Scalar-Field Potential
    C. Li, D.E. Holz, and A. Cooray, Phys. Rev. D75, 103503, astro-ph/0611128

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