Since 2002 Perimeter Institute has been recording seminars, conference talks, and public outreach events using video cameras installed in our lecture theatres. Perimeter now has 7 formal presentation spaces for its many scientific conferences, seminars, workshops and educational outreach activities, all with advanced audio-visual technical capabilities. Recordings of events in these areas are all available On-Demand from this Video Library and on Perimeter Institute Recorded Seminar Archive (PIRSA). PIRSA is a permanent, free, searchable, and citable archive of recorded seminars from relevant bodies in physics. This resource has been partially modelled after Cornell University's arXiv.org.
It is an important task to embed inflation in a fundamental microphysical theory such as string theory. Since string theory possesses a vast landscape of 4-dimensional theories, we would like to know which portions contain inflation and which do not. I prove a no-go theorem that inflation and de Sitter vacua are forbidden in an exponentially large number of infinite families of simple and well understood compactifications of type IIA string theory. I also mention more complicated and less well understood compactifications, which may have the ingredients for our cosmology.
Directional detection of dark matter can provide unambiguous observation of dark matter (DM) interactions even in the presence of insidious backgrounds. The DM-TPC collaboration is developing a detector with the goal of measuring the direction and sense (\'\'head-tail\'\') of nuclear recoils produced in spin-dependent DM interactions. The detector consists of a low pressure TPC with optical readout filled with CF4 gas at low pressure. A collision between a WIMP with a gas molecule results in a nucleus recoil of 1-2 mm.
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.