Non-Canonical Scalar Fields and Their Applications in Cosmology and Astrophysics.

Abstract

In this thesis we will discuss several issues concerning cosmological applications of non-canonical scalar fields, which are generically referred to as k-essence. First, we consider two examples of k-essence. These are the rolling tachyon and static spherically symmetric solutions of non-canonical scalar fields in flat space.

Next, we consider static spherically symmetric solutions of non-canonical scalar fields coupled to gravity as a way to explain dark matter halos as a coherent state of the scalar field. The non-trivial solutions have negative energy density near the origin, though the total energy is positive.

After this we show that, for general scalar fields, stationary configurations are possible for shift symmetric theories only.

The next discussion outlines a general program for reconstructing the action of non-canonical single field inflation models from CMBR power spectrum data.

Finally, we study a novel means of coupling neutrinos to a Lorentz violating k-essence background. We first look into the effect k-essence has on the neutrino dispersion relation, and derive the neutrino velocity in a k-essence background. Next, we look at the effect on neutrino oscillations.