A classical Hamiltonian system can be reduced to a subsystem of "relevant observables" using the pull-back under a Poisson embedding of the "relevant phase space" into the "full phase space". Since a quantum theory can be thought of a noncommutative phase space, one encounters the problem of the embedding of noncommutative spaces, when one tries to extend the reduction via a pull-back to a quantum theory. This problem can be solved for a class of physically interesting quantum systems and embeddings using an analogy to finding the base space of an embedded fibre bundle via the projection in the full fibre bundle. The resulting construction is then applied to Loop Quantum Gravity to extract a cosmological sector. This sector turns out to be similar but not equivalent to Loop Quantum Cosmology.
Non-Gaussianities are a generic prediction of multi-field inflationary models and within reach of upcoming experiments. After reviewing current observational limits and the physical origin of a non-zero three point correlation function, I will discuss the possibility of detectable non-Gaussian signatures in a certain class of multi-field inflationary models, upon which assisted inflation/N-flation lies. Using the delta-N formalism within the slow roll approximation and focusing on N-flation (quadratic potentials without cross-coupling), we will see that said signatures are suppressed as the number of e-foldings grows, and that this suppression is increased in models with a broad spectrum of masses.
We thus conclude that the production of a large non-Gaussian signal in models of this type is very unlikely.
A number of mechanisms have been introduced in previous literature that might be responsible for transitions between metastable minima in a scalar field theory coupled to gravity. The connection between these transition mechanisms has remained unclear, and current formulations of eternal inflation only include a subset of the allowed processes. In the first part of this talk, I will discuss how a number of transition mechanisms can be unified in the thin-wall limit, with interesting consequences for quantum cosmology and eternal inflation. I will then discuss making predictions in an eternally inflating universe, and introduce a measure for eternal inflation that is based on transitions rather than vacua.
We will discuss applications of the recently developed twistor-space methods in perturbative quantum field-theory. The two central topics will be 1) the unitarity bootstrap approach to hard scattering amplitudes in QCD and 2) the analysis of the UV structure of N=8 supergravity.
Quantum gravity in an AdS space-time is described by an SU(N) Yang-Mills theory on a sphere, a bounded many-body system. We argue that in the high temperature phase the theory is intrinsically non-perturbative in the large N limit. At any nonzero value of the \\\'t Hooft coupling $lambda$, an exponentially large (in N^2) number of free theory states of wide energy range (of order N) mix under the interaction. As a result the planar perturbation theory breaks down. We argue that an arrow of time emerges and the dual string configuration should be interpreted as a stringy black hole
Due to recent, as well as less recent, work on perturbative N=8 supergravity and N=4 super Yang-Mills in 4d, the two theories are appearing more and more closely related. These relations include similar \"MHV-rule\" constructions, one-loop structure and, perhaps, the same UV behavior, namely UV finiteness. This talk introduces some of the methods to study the relations.
In the context of AdS/CFT, it has been recently proposed that Wilson loops in higher representation of the gauge group have a dual description in terms of D-branes in AdS_5xS^5. After reviewing this new dictionary, I will present a computation of correlators between chiral primaries of N=4 SYM and Wilson loops in large symmetric and antisymmetric representations. These correlators can be computed both in supergravity using D-branes and in gauge theory from a matrix model, with precise agreement between the two sides
It has been conjectured that maximally supersymmetric SU(N) Yang-Mills theory is dual to a String Theory on asymptotically AdS_5 times S^5 backgrounds. This is known as the AdS/CFT correspondence. In this talk I will show how using one-loop calculations in the gauge theory, one can study the emergence of the dual String Theory. We will see, quite explicitly, the emergence of closed strings, D-branes, open strings and space-time itself. This is done in a reduced sector (SU(2) sector), where the gauge theory can be written as Matrix Quantum Mechanics. This simple sector provides a toy model of a non-perturbative quantum theory of gravity.