14th International Symposium on Particles, Strings and Cosmology (PASCOS '08)
A class of non-canonical inflationary models is identified, where the leading-order contribution to the non-Gaussianity of the curvature perturbation is determined by the sound speed of the fluctuations in the inflaton field. Included in this class of models is the effective action for multiple coincident branes in the finite n limit. The action for this configuration is determined using a powerful iterative technique, based upon the fundamental representation of SU(2).
Considering gravitino dark matter scenarios, cosmological constraints on the sparticle masses and on the reheating temperature of inflation will be discussed. These constraints are relevant for prospects of phenomenology at the LHC and for our understanding of inflation and the baryon asymmetry of the Universe.
I point out that there is a curvature singularity problem appearing on non-linear level that generally plagues f(R) models that modify Einstein gravity in the infrared. It is caused by the fact that for the effective scalar degree of freedom, the curvatur
We consider the most general treatment of primordial non-Gaussianities, arising from modifying the initial state. Besides considering non-Gaussian effects due to subhorizon particle production, we parameterize the initial non-Gaussian features in terms of a Boundary Effective Field Theory (BEFT). Both effects contribute to the final result for the bispectrum, and we use this to put constraints on the initial state.
We consider the gravity in the system consisting of the BPS D3-brane embedded in the flat background geometry, produced by the solutions of the supergravity. The effective action for this system is represented by the sum of the Hilbert-Einstein and DBI actions. We derive the Wheeler-De Witt equation for this system and obtain analytical solutions in some special cases. We also calculate tunneling probability from Planckian size of D3-brane to the classical regime. This paper appeared in Phys. Rev. D 77, 066017 (2008)
We derive a simple consistency relation from the running of the tensor-to-scalar ratio. This new relation is first order in the slow-roll approximation. While for single field models we can obtain what can be found by using other observables, multi-field cases in general give non-trivial contributions dependent on the geometry of the field space and the inflationary dynamics, which can be probed observationally from this relation.
We construct a consistent supersymmetric action for chiral and vector multiplets living on codimension-two branes in a six-dimensional chiral gauged supergravity. A nonzero brane tension can be compatible with the bulk supersymmetry by introducing a brane-localized Fayet-Iliopoulos term proportional to the brane tension. Moreover, we show that a brane chiral multiplet with nonzero R charge has a nontrivial coupling to the extra component of the U(1)_R gauge field strength and a singular scalar self-interaction term.
I will present a model of inflation in string theory, where the inflaton field corresponds to a Wilson line in the worldvolume of a D-brane, and in the presence of magnetic flux. Inflation ends in a hybrid fashion, when the Wilson line achieves a critical value and an open string mode becomes tachyonic. This scenario predicts a nearly flat, or red tilted, spectrum of scalar perturbations, with negligible primordial gravitational waves. Interestingly, there is a simple compactification in which the eta-problem, appearing in models of brane inflation, is absent.
About 20-30 years ago, scientific community was interested in knowing whether dark matter can carry gauge charges. The answer was found to be no. Today, we can ask a similar question: Can dark energy carry gauge charges? The answer this time seems to be yes. We study the possibility that the current accelerated expansion of the universe is driven by the vacuum energy density of a colored scalar field which is responsible for a phase transition in which the gauge SU(3)_c symmetry breaks.
We study the cosmological evolution of an induced gravity model with a self-interacting scalar field $sigma$ and in the presence of matter and radiation. Such model leads to Einstein Gravity plus a cosmological constant as a stable attractor among homogeneous cosmologies and is therefore a viable dark-energy (DE) model for a wide range of scalar field initial conditions and values for its positive $gamma$ coupling to the Ricci curvature $gamma sigma^{2}R$.