Aspects of inflation in string theory.

by Daniel Baumann

In this thesis we make small steps towards the ambitious goal of a microphysical understanding of the inflationary era in the early universe. We identify three key questions that require a proper understanding of the ultraviolet limit of the theory: (i) the delicate flatness of the inflaton potential, (ii) the possibility of observable gravitational waves and (iii) a large non-Gaussianity of the primordial density fluctuations. We study these fundamental aspects of inflation in the context of string theory.;V (&phis;): In the first half of the thesis, we give the first fully explicit derivation of the potential for warped D-brane inflation. The analysis exposes the eta-problem, relates effective parameters in the inflaton Lagrangian to microscopic string theory input, and illustrates important correlations between the parameters of the potential. We show that compactification constraints significantly limit the possibility of obtaining inflationary solutions in these scenarios.;r: All inflationary models that predict an observable gravitational wave signal require that the inflaton field evolves over a super-Planckian range. In the second half of the thesis, we derive a microscopic bound on the maximal inflaton field variation for D-brane models. The bound arises from the compact nature of the extra dimensions and puts a strong upper limit on the gravitational wave signal.;fNL: Finally, we explain that our limit on the field range also significantly constrains the parameter space of Dirac-Born-Infeld inflation. In this case the bound strongly restricts the possibility of a large non-Gaussianity in the primordial fluctuations.

286 pages, NOOKstudy eTextbook