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.

Thesis (D.M.A.)--University of Texas at Austin, 1999. / Vita. Includes bibliographical references (leaves 81-83). Available also in a digital version from Dissertation Abstracts.

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.

The art of fugue, BWV 1080 / Johann Sebastian Bach -- String quartet no. 64 in D major, op. 76 no. 5 / Franz Joseph Haydn -- String quartet no. 10 in E flat major, op. 51 "Slavonic" / Antonin Dvorak -- Pannonia boundless / Aleksandra Vrebalov. / text

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This thesis deals with string theory at finite temperature. String theory has attracted considerable attention in recent years because of its ability to unify the fundamental forces and particles in nature and provide a quantized description of gravity. However, many aspects of this theory remain mysterious, including its behavior at high temperature. One guiding principle for finite temperature string theory is the observation that a quantum theory at finite temperature can be recast as a zero-temperature theory in which a Euclidean time dimension is compactified on a circle. This temperature/radius correspondence holds in quantum mechanics as well as quantum field theory, and is normally assumed to hold in string theory as well. However it was shown recently that this correspondence fails for a class of string theories, called heterotic strings. This motivates a search for an alternate way to restore this correspondence, as well as a reevaluation of the thermodynamic behaviour of other classes of string theories, namely Type~II and Type~I. We find that contrary to the established wisdom, all ten dimensional string theories have a similar behaviour at finite temperature. This also leads us to the conclusion that the Heterotic and Type~I theory behave in a dual way at finite temperature.

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.