String Theory, Space-Time Non-Commutativity and Structure Formation

A natural consequence of string theory is a non-commutative structure of space-time on microscopic scales. The existence of a minimal length, and a modification of the effective field theory are two consequences of this space-time non-commutativity. I will first explore some consequences of the modifications of the effective field theory for structure formation in the context of an inflationary cosmology. Then, I will explore the possibility that the existence of a minimal length will lead to a structure formation scenario different from inflation. Specifically, I will discuss recent work on string gas cosmology.Comment: 12 pages, 2 figures, based on an invited talk at the 21st Nishinomiya-Yukawa Memorial Symposium, Nov. 11 - 16, 2006, to be publ. in the proceedings (Prog. Theor. Phys. Suppl.

Principles, Progress and Problems in Inflationary Cosmology

Inflationary cosmology has become one of the cornerstones of modern cosmology. Inflation was the first theory within which it was possible to make predictions about the structure of the Universe on large scales, based on causal physics. The development of the inflationary Universe scenario has opened up a new and extremely promising avenue for connecting fundamental physics with experiment. This article summarizes the principles of inflationary cosmology, discusses progress in the field, focusing in particular on the mechanism by which initial quantum vacuum fluctuations develop into the seeds for the large-scale structure in the Universe, and highlights the important unsolved problems of the scenario. The case is made that new input from fundamental physics is needed in order to solve these problems, and that thus early Universe cosmology can become the testing ground for trans-Planckian physics.Comment: 8 pages, 8 figures commissioned article for the AAPPS Bulletin, appeared in 200

Cosmology of the Very Early Universe

In these lectures I focus on early universe models which can explain the currently observed structure on large scales. I begin with a survey of inflationary cosmology, the current paradigm for understanding the origin of the universe as we observe it today. I will discuss some progress and problems in inflationary cosmology before moving on to a description of two alternative scenarios - the Matter Bounce and String Gas Cosmology. All early universe models connect to observations via the evolution of cosmological perturbations - a topic which will be discussed in detail in these lectures.Comment: 38 pages, 15 figures, to be published in the proceedings of the XIV Special Course in Astronomy, Observatorio Nacional, Brazi