Talks

Recent results have shown that quantum computers can approximate the value of a tensor network efficiently. These results have initiated a search for tensor networks which contract to computationally interesting quantities. Topological Lattice Field Theories (TLFTs) are one source of such networks; when defined appropriately, networks arising from TLFTs contract to give topological invariants. In this elementary talk, we will define and classify TLFTs which lead to invariants of surfaces, and sketch out the corresponding quantum algorithm. Our exposition will be targetted at a general mathematically-inclined audience; no previous knowledge of field theories is required.

We examine the embedding of dark energy energy models based upon supergravity. We analyse the structure of the soft supersymmetry breaking terms in presence of dark energy. We pay attention to their dependence on the quintessence field and to the electroweak symmetry breaking, ie the pattern of fermions masses at low energy within the MSSM coupled to quintessence. In particular, we compute explicitly how the fermion masses generated through the Higgs mechanism depend on the quintessence field for a general model of quintessence. Fifth force and equivalence principle violations are potentially present as the vev of the Higgs bosons become quintessence field dependent. We emphasize that equivalence principle violations are a generic consequence of the fact that, in the MSSM, the fermions couple diffeently to the two Higgs doublets. Finally, we also discuss how the scaling of the cold dark and baryonic matter energy density is modified.

This course provides a thorough introduction to the bosonic string based on the Polyakov path integral and conformal field theory. We introduce central ideas of string theory, the tools of conformal field theory, the Polyakov path integral, and the covariant quantization of the string. We discuss string interactions and cover the tree-level and one loop amplitudes. More advanced topics such as T-duality and D-branes will be taught as part of the course. The course is geared for M.Sc. and Ph.D. students enrolled in Collaborative Ph.D. Program in Theoretical Physics. Required previous course work: Quantum Field Theory (AM516 or equivalent). The course evaluation will be based on regular problem sets that will be handed in during the term. The primary text is the book: 'String theory. Vol. 1: An introduction to the bosonic string. J. Polchinski (Santa Barbara, KITP) . 1998. 402pp. Cambridge, UK: Univ. Pr. (1998) 402 p.' All interested students should contact Alex Buchel at abuchel@uwo.ca as soon as possible.

This course provides a thorough introduction to the bosonic string based on the Polyakov path integral and conformal field theory. We introduce central ideas of string theory, the tools of conformal field theory, the Polyakov path integral, and the covariant quantization of the string. We discuss string interactions and cover the tree-level and one loop amplitudes. More advanced topics such as T-duality and D-branes will be taught as part of the course. The course is geared for M.Sc. and Ph.D. students enrolled in Collaborative Ph.D. Program in Theoretical Physics. Required previous course work: Quantum Field Theory (AM516 or equivalent). The course evaluation will be based on regular problem sets that will be handed in during the term. The primary text is the book: 'String theory. Vol. 1: An introduction to the bosonic string. J. Polchinski (Santa Barbara, KITP) . 1998. 402pp. Cambridge, UK: Univ. Pr. (1998) 402 p.' All interested students should contact Alex Buchel at abuchel@uwo.ca as soon as possible.

In this talk I will review how ideas borrowed from perturbative Quantum Gravity and Effective Field Theory (EFT) in Particle Physics can be applied to problems in General Relativity (GR), such as calculating gravitational wave emission by inspiralling spinning binary systems, including finite size effects and absorption. I will discuss in somewhat more detail how to account for dissipative effects, where the GR/EFT duality is used to predict the power loss due to absorption in the dynamics of binary spinning Black Holes.

We derive a universal upper bound on the weight of the lowest primary operator in any two-dimensional conformal field theory with a given central charge. Translated into gravitational language using the AdS/CFT dictionary, our result proves rigorously that the lightest massive state in any theory of 3D gravity and matter with negative cosmological constant can be no heavier than a particular function the cosmological constant and the Planck scale. For a large AdS space, the lower bound approaches the mass of the lightest BTZ black hole. The derivation applies at finite central charge and does not rely on an asymptotic expansion at large central charge, or on any use of semiclassical or bulk physics. Neither does our proof rely on any special property of the CFT such as supersymmetry or holomorphic factorization. The only assumptions are unitarity, modular invariance, and a discrete spectrum. Our proof firmly demonstrates for the first time that there exists a universal center-of-mass energy beyond which a theory of 'pure' quantum gravity can never consistently be extended.

Condensed matter systems at ultra low-temperature that show purely quantum phenomena – even on big scales (superfluidity, superconductivity, Bose-Einstein condensates); measurements in the quantum world; probing the foundations of quantum theory.

Fundamental interactions between elementary particles, using deep ideas involving mathematical symmetry for restoring unity to the fundamental laws of nature (strong and weak nuclear forces, electromagnetism and gravity).

Many aspects of geometry, black holes, novel views on the evolution of the universe (was there something before the Big Bang?), the interplay and unification of general relativity and quantum physics, and science of consciousness.

Cosmology, in particular applying the physics of elementary particles to the extremely hot and violent conditions of the early universe, and exploring deep questions about the big bang, the fate of our universe, and the hope for intelligent life (here or elsewhere)