Search Talks

Surprisingly, several basic questions in classical and quantum gravity, which were resolved some 40-50 years ago for zero $\Lambda$, still remain open in the $\Lambda >0$ case. In particular, for $\Lambda >0$, we still do not have a satisfactory notion of gravitational radiation or Bondi 4-momentum in exact general relativity, nor a positive energy theorem. Similarly, the standard constructions of `in' and `out' Hilbert spaces that we routinely use (e.g. in the analysis of black hole evaporation) do not extend to the $\Lambda >0$ case. In this talk I will present some illustrative examples of these quandaries and introduce a systematic approach to resolve the open issues.

 

Thanks to the spectacular observational advances since the 1990s, a `standard model' of the early universe has now emerged. However, since it is based on quantum field theory in curved space-times, it is not applicable in the Planck era. Using techniques from loop quantum gravity, the theory can be extended over the 12 orders of magnitude in density and curvature from the onset of inflation all the way back to the Planck regime, providing us with a possible completion of the standard model.

Contrary to a wide-spread belief, the resulting pre-inflationary dynamics can have observational consequences for the longest wave length modes of cosmological perturbations. Thus, there is now an an interesting interplay between fundamental theory and observations. The talk will provide a broad overview of these results addressed to non-experts.

Web-links:

Viewpoint: A glance at the earliest universe; APS Physics Spotlighting Exceptional Research: http://physics.aps.org/articles/v5/142

U tube video

http://www.youtube.com/watch?v=IFcQuEw0oY8&feature=c4-overview&list=UUtOgK

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In holographic duality a gravitational spacetime emerges as an equivalent description of a lower-dimensional conformal field theory (CFT) living on the asymptotic boundary. Traditionally, the dimension not present in the CFT is interpreted in terms of its Renormalisation Group flow. In this talk I exploit the relation between boundary entanglement entropies and bulk minimal surfaces to define a quantitative framework for the holographic Renormalisation Group, in which quantum information theory plays a fundamental role. I will provide operational, quantitative, information-theoretic characterizations of several geometric concepts in asymptotically AdS3 spacetimes, including the radial direction and lengths of bulk curves.

Perhaps the biggest conceptual benefit of the information-theoretic framework for holographic Renormalisation Group is a quantitative correspondence between holography and the Multi-Scale Entanglement Renormalisation Ansatz (MERA). I also discuss prospects for understanding the near-horizon structure of black holes.

The last decade has seen a wave of characterizations of quantum theory using the formalism of generalized probability theory.

In this talk, I will introduce a novel operational approach to characterizing and reconstructing quantum theory which puts an observer’s information acquisition -- rather than the probability structure – centre stage. In particular, we consider an observer interrogating a system with binary questions and explain how an elementary set of rules governing the observer’s acquisition of information about the system leads to qubit quantum theory. The derivation is constructive, elucidating, among other things, the origin of entanglement, monogamy and more generally the correlation structure. This approach also yields a new characterization of pure states in terms of ‘conserved informational charges’ which, in turn, define the unitary group.

In this talk I will propose a general correspondence which associates a non-perturbative quantum mechanical operator to a toric Calabi-Yau manifold, and I will propose a conjectural expression for its spectral determinant. As a consequence of these results, I will derive an exact quantization condition for the operator spectrum. I will give a concrete illustration of this conjecture by focusing on the example of local P2. This approach also provides a non-perturbative Fermi gas picture of topological strings on toric background and suggests the existence of an underlying theory of M2 branes behind this formulation.