Aspects of D-brane inflation

Inflation has been suggested as a solution to cosmological problems but it ultimately needs to be derived from a fundamental theory such as string theory. In this thesis we study the embedding of inflation into string theory using the D-brane inflation scenario as case study. We first review the relevant aspects of string compactifications and D-branes and construct the effective action of the inflationary D3-brane. We then study multifield D-brane inflation including compactification corrections to the inflaton action that arise from UV deformations of a warped throat geometry emerging from the ISD supergravity solution. One particular issue here is to investigate in detail the cosmological consequences of realistic angular dependent potentials in the D-brane inflation scenario in a fully UV/IR consistent way. Embedding a warped throat into a compact Calabi-Yau space with all moduli stabilized breaks the no-scale structure and induces angular dependence in the potential of the probe D3-brane. We solve the D3-brane equations of motion from the DBI action in the warped deformed conifold including linearized as well as non-linear perturbations around the ISD supergravity solution. Our numerical solutions show that angular dependence is a next to leading order correction to the dominant radial motion of the brane, however, just as angular motion typically increases the amount of inflation (spinflation), having additional angular dependence from linearized perturbations also increases the amount of inflation

Temperature in the Throat

We study the temperature of extended objects in string theory. Rotating probe D-branes admit horizons and temperatures a la Unruh effect. We find that the induced metrics on slow rotating probe D1-branes in holographic string solutions including warped Calabi-Yau throats have distinct thermal horizons with characteristic Hawking temperatures even if there is no black hole in the bulk Calabi-Yau. Taking the UV/IR limits of the solution, we show that the world volume black hole nucleation depends on the deformation and the warping of the throat. We find that world volume horizons and temperatures of expected features form not in the regular confining IR region but in the singular nonconfining UV solution. In the conformal limit of the UV, we find horizons and temperatures similar to those on rotating probes in the AdS throat found in the literature. In this case, we also find that activating a background gauge field form the U(1) R--symmetry modifies the induced metric with its temperature describing two different classes of black hole solutions.Comment: Revised, extended and published versio

Spinflation with Angular Potentials

We investigate in detail the cosmological consequences of realistic angular dependent potentials in the brane inflation scenario. Embedding a warped throat into a compact Calabi-Yau space with all moduli stabilized breaks the no-scale structure and induces angular dependence in the potential of the probe D3-brane. We solve the equations of motion from the DBI action in the warped deformed conifold including linearized perturbations around the imaginary self-dual solution. Our numerical solutions show that angular dependence is a next to leading order correction to the dominant radial motion of the brane, however, just as angular motion typically increases the amount of inflation (spinflation), having additional angular dependence also increases the amount of inflation. We also derive an analytic approximation for the number of e-foldings along the DBI trajectory in terms of the compactification parameters.Comment: 20 pages, 10 figures. Revised to published version: minor errors corrected, references and discussion adde