This series consists of talks in the areas of Cosmology, Gravitation and Particle Physics.
The most remarkable recent discovery in fundamental physics is that the Universe is undergoing accelerated expansion. A proper understanding of its physical origin forces us to make a hard choice between dynamical and environmental scenarios. The former approach predicts the existence of a new long distance physics in the gravitational sector, while the second relies on the vast landscape of vacua with different values of the cosmological constant. I will discuss achievements and shortcomings of both approaches, and illustrate them in the concrete examples.
Cosmological observations will soon distinguish between the standard slow roll inflationary paradigm and some of its recently developed alternatives. Driven by developments in string theory, many new models include features such as non-minimal kinetic terms, leading to large non-gaussianities, making them observationally testable in the CMB. Models of slow roll inflation can also give rise to large non- gaussianities if the initial inflationary state was sufficiently excited, with a shape dependence that will be clearly distinguishable.
I\'ll introduce a particular class of fundamental string configurations in the form of closed loops stabilized by internal dynamics. I\\\'ll describe their classical treatment and embedding in models of string cosmology. I\\\'ll present the quantum version and the semiclassical limit that provides a microscopic description of dipole black rings. I\\\'ll show the parametric matching between the degeneracy of microstates and the entropy of the supergravity solution.
The history of human knowledge is often highlighted by our efforts to explore beyond our apparent horizon. In this talk, I will describe how this challenge has now evolved into our quest to understand the physics at/beyond the cosmological horizon, some twenty orders of magnitude above Columbuss original goal.
We consider a consistent construction of the supersymmetric action for a codimension-two brane in six-dimensional Salam-Sezgin supergravity. When the brane carries a tension, we supersymmetrize the brane tension action by introducing a localized Fayet-Iliopoulos term on the brane and modifying the bulk SUSY transformations.
As a result, we find that among the axisymmetric vacua of the system, the unwarped background with football-shaped extra dimensions respects N=1 supersymmetry. We extend the analysis to include the brane multiplets with the couplings to the bulk fields.
Linear cosmological perturbation theory is pivotal to a theoretical understanding of current cosmological experimental data provided e.g. by cosmic microwave anisotropy probes. A key issue in this theory is to extract the gauge invariant degrees of freedom which allow unambiguous comparison between theory and experiment. In this talk we will present a manifeslty gauge invariant formulation of general relativistic perturbation theory.
We have two strong reasons to argue that Einstein\'s theory of general relativity may be incomplete. First, given that it cannot be expressed within a consistent quantum field theory there is reason to expect higher energy corrections. Second, the observation that we are undergoing a current epoch of accelerated expansion might indicate that our understanding of gravity breaks down at the largest scales.