No description available.

No description available.

Thesis (Ph. D.)--University of Chicago, Dept. of Physics, August 1997. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--Rutgers University, 2008. / "Graduate Program in Physics and Astronomy." Includes bibliographical references (p. 93-97).

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (p. 131-133).

Thesis (Ph. D.)--University of Chicago, Dept. of Physics, December 2003. / Includes bibliographical references. Also available on the Internet.

Diss. (sammanfattning) Uppsala : Univ., 2005. / Härtill 6 uppsatser. Med sammanfattning på svenska med titel: Strängteori vid horisonten.

Thesis (Ph. D.)--University of Chicago, Department of Physics, August, 2003. / Includes bibliographical references. Also available on the Internet.

No description available.

Though historically the word "tachyon" has been used to describe hypothetical particles which propagate faster than the speed of light, in a more modern context the term has been recycled to refer to certain unstable states in field theory. This thesis explores the role of tachyonic instabilities in cosmology considering tachyons which arise in string theory and also more conventional, field theoretic instabilities. Our study of such instabilities is, in part, motivated by attempts to embed inflation into string theory. We will argue that the study of string theory models of inflation is well-motivated and may provide a rare potential observational window into string physics. / After reviewing the necessary background material concerning inflation, cosmological perturbation theory and tachyonic instabilities we study in detail the dynamics of the tachyonic instability which marks the end of a particular string theory model of inflation, focusing on the processes of reheating and cosmic string production. We show that the peculiar dynamics of the open string tachyon leads to various novelties in these processes and consider also potential observational consequences. / We consider tachyonic preheating at the end of hybrid inflation in a conventional field theory setting and show that the preheating process can leave an observable imprint on the Cosmic Microwave Background, either through n = 4 contamination of the power spectrum or else through large nongaussian signatures. The possibility of large nongaussianity is particularly interesting since it demonstrates that hybrid inflation provides one of the few well-motivated models which can generate an observable nongaussian signature. / Finally, we study a novel string theoretic model of inflation, p-adic inflation. This model is nonlocal, however, it is free of the usual problems (such as ghosts) which plague nonlocal theories. Furthermore, the nonlocal structure of the theory leads to a variety of unexpected dynamics including the possiblity of a slowly rolling inflaton, despite an extremely steep potential.