Attractive Lagrangians for Noncanonical Inflation

Treating inflation as an effective theory, we expect the effective Lagrangian to contain higher-dimensional kinetic operators suppressed by the scale of UV physics. When these operators are powers of the inflaton kinetic energy, the scalar field can support a period of noncanonical inflation which is smoothly connected to the usual slow-roll inflation. We show how to construct noncanonical inflationary solutions to the equations of motion for the first time, and demonstrate that noncanonical inflation is an attractor in phase space for all small- and large-field models. We identify some sufficient conditions on the functional form of the Lagrangian that lead to successful noncanonical inflation since not every Lagrangian with higher-dimensional kinetic operators can support noncanonical inflation. This extends the class of known viable Lagrangians and excludes many Lagrangians which do not work.Comment: 39 pages, 9 figures. v2. Fixed typos, added reference, small changes to examples; v3. Added discussion of field redefinitions, added references, matches published versio

Initial Conditions for Non-Canonical Inflation

We investigate the dynamics of homogeneous phase space for single-field models of inflation. Inflationary trajectories are formally attractors in phase space, but since in practice not all initial conditions lead to them, some degree of fine tuning is required for successful inflation. We explore how the dynamics of non-canonical inflation, which has additional kinetic terms that are powers of the kinetic energy, can play a role in ameliorating the initial conditions fine tuning problem. We present a qualitative analysis of inflationary phase space based on the dynamical behavior of the scalar field. This allows us to construct the flow of trajectories, finding that trajectories generically decay towards the inflationary solution at a steeper angle for non-canonical kinetic terms, in comparison to canonical kinetic terms, so that a larger fraction of the initial-conditions space leads to inflation. Thus, non-canonical kinetic terms can be important for removing the initial conditions fine-tuning problem of some small-field inflation models.Comment: 15 pages, 9 figure

D3-brane Vacua in Stabilized Compactifications

D3-branes feel no force in no-scale flux compactifications of type IIB string theory, but the nonperturbative effects required to stabilize the Kahler moduli break the no-scale structure and generate a potential for D3-brane motion, confining the branes to certain loci. D3-branes away from these loci break supersymmetry spontaneously, by an F-term. We present the general conditions for supersymmetric D3-brane vacua in models with a single Kahler modulus, then explicitly calculate these vacua for D3-branes moving on the tip of the warped deformed conifold. We find both continuous moduli spaces and isolated vacua. In addition, we show that anti-D3-branes and D3-branes are localized to the same regions by the nonperturbative potential, avoiding a potential obstacle to brane inflation. We apply these results to determine whether angular motion of a brane in a throat could play an important role in inflation, and find that any inflation along the angular directions is short-lived because the field space is very small.Comment: 30 pages, LaTeX. v2: references added, typos fixe

Probing the Geometry of Warped String Compactifications at the LHC

Warped string compactifications, characterized by non-singular behavior of the metric in the infrared (IR), feature departures from the usual anti-de Sitter warped extra dimensions. We study the implications of the smooth IR cutoff for Randall-Sundrum (RS) type models. We find that the phenomenology of the KK gravitons (including their masses and couplings) depends sensitively on the precise shape of the warp factor in the IR. In particular, we analyze the warped deformed conifold and find that the spectrum differs significantly from that of RS, and present a simple prescription (a mass gap ansatz) which can be used to study the phenomenology of IR modifications to 5-d warped extra dimensions.Comment: 4 pages, 4 figures; v2. typos corrected, references added, improved resolution of Figure

Multifield DBI Inflation and Non-Gaussianities

We analyze the trajectories for multifield DBI inflation, which can arise in brane inflation models, and show that the trajectories are the same as in typical slow roll inflation. We calculate the power spectrum and find that the higher derivative terms of the DBI action lead to a suppression of the contribution from the isocurvature perturbations. We also calculate the bispectrum generated by the isocurvature perturbation, and find that it leads to distinctive features.Comment: 7 pages, 4 figures; v2. references added; v3. typos corrected, matches published versio