Talks

In these lectures, we will study the bosonic theory of higher-spin gravity in four dimensions. After discussing the reasons for interest in the theory, we will focus on the equations of motion and their content. We will aim to construct the equations from the ground up in a motivated way. The logical order will differ somewhat from standard introductions. As preliminaries, we will discuss the geometry of spinors and twistors in (anti) de Sitter space, along with various viewpoints on free massless fields with arbitrary spin. An ulterior goal of the lectures is to introduce a new version of the theory (arXiv:1502.06685), formulated on a fixed (A)dS background

Freeze-in is a general and calculable mechanism for dark matter production in the early universe. Assuming a standard cosmological history, such a framework predicts metastable particles with a lifetime generically too long to observe their decays in a collider environment. In this talk I will report work in progress where we consider alternative cosmologies, where entropy dumped in the primordial Standard Model plasma leads to shorter lifetime for the metastable particles in order to reproduce the observed dark matter density. Famous examples are moduli decays in SUSY theories and inflationary reheating. Remarkably, for a large region of the parameter space the decay lengths are in the displaced vertex range and they can be observable at present and future colliders.

A classical Einstein-Rosen bridge changes the topology of spacetime,allowing (for example) electric field lines to penetrate it. It has recently been suggested that in the bulk of a theory of quantum gravity, the quantum entanglement of ordinary perturbative quanta should be viewed as creating a quantum version of an Einstein-Rosen bridge between the quanta, or a “quantum wormhole”. For this “ER=EPR” correspondence to make sense it then seems necessary for a quantum wormhole to allow (for example) electric field lines to penetrate it. I will discuss (within low-energy effective field theory) whether or not this happens.

I propose a quantum gravity model in which the fundamental degrees of freedom are pure information bits for both discrete space-time points and links connecting them. The Hamiltonian is a very simple network model consisting of a ferromagnetic Ising model for space-time vertices and an antiferromagnetic Ising model for the links. As a result of the frustration arising between these two terms, the ground state self-organizes as a new type of low-clustering graph with finite Hausdorff dimension. The model has three quantum phases: a mean field phase in which the spectral and Hausdorff dimensions coincide and are larger then 4. A fluctuations-dominated phase in which the Hausdorff dimension can only be 4 and the spectral dimension is lower than the Hausdorff dimension and a disordered phase in which there is no space-time interpretation. The large-scale dimension 4 of the universe is related to the upper critical dimension 4 of the Ising model. An ultraviolet fixed point at the lower critical dimension of the Ising model implies the absence of space-time at very small scales. At finite temperatures the universe emerges without big bang and without singularities from a ferromagnetic phase transition in which space-time itself forms out of a hot soup of information bits. When the temperature is lowered the universe unfolds and expands by lowering its connectivity, a mechanism I have called topological expansion. The model admits also macroscopic black hole configurations corresponding to graphs containing holes with no space time inside and around which there are "Schwarzschild-like horizons" with a lower spectral dimension and an entropy proportional to their surface. 

The known basic building blocks of matter, the quarks and leptons, come in three generations or flavors.
The masses and interactions of the different flavors show a very hierarchical structure and the origin of these hierarchies remains an unsolved mystery of particle physics. The same hierarchies lead to a very high sensitivity of flavor changing processes to new undiscovered particles even outside the reach of direct searches at particle colliders.
In this colloquium I will present recent developments in constructing a theory of flavor and highlight the complementarity of flavor, Higgs, and collider physics in searching for new phenomena at the TeV scale and beyond.

String Theory LEGOs for Black Holes

Four decades ago, Stephen Hawking posed a paradox about black holes and quantum theory that still challenges the imaginations of theoretical physicists today. One of the most promising approaches to resolving the "information paradox" (the notion that nothing, not even information itself, survives beyond a black hole's point-of-no-return event horizon) is string theory, a part of modern physics that has wiggled its way into the popular consciousness.

Dr. Amanda Peet, a physicist at the University of Toronto, will describe how the string toolbox allows study of the extreme physics of black holes in new and fruitful ways. Dr. Peet will unpack that toolbox to reveal the versatility of strings and (mem)branes, and will explore the intriguing notion that the world may be a hologram.

Most of the matter in the Universe is dark; determining the composition and interactions of this dark matter is among the defining challenges in particle physics today. I will briefly summarize the present status of dark matter searches and the case for exploration beyond the WIMP paradigm, particularly “light dark matter” close to but beneath the weak scale. I will define sharp milestones in sensitivity needed to decisively explore the best-motivated light dark matter scenarios, and describe experimental techniques to reach these milestones over the next several years.

In these lectures, we will study the bosonic theory of higher-spin gravity in four dimensions. After discussing the reasons for interest in the theory, we will focus on the equations of motion and their content. We will aim to construct the equations from the ground up in a motivated way. The logical order will differ somewhat from standard introductions. As preliminaries, we will discuss the geometry of spinors and twistors in (anti) de Sitter space, along with various viewpoints on free massless fields with arbitrary spin. An ulterior goal of the lectures is to introduce a new version of the theory (arXiv:1502.06685), formulated on a fixed (A)dS background.

Using quantum control in foundational experiments allows new theoretical and experimental possibilities. We show how, e.g.,  quantum controlling devices reverse a temporal ordering in  detection. We consider probing of wave–particle duality in   quantum-controlled and the entanglement-assisted delayed-choice experiments. Then we discuss other situations where quantum control may be useful, and finally demonstrate how the techniques we developed are applied to the study of  consistency of the classically reasonable requirements.  In a version of the delayed-choice experiment which ostensibly combines determinism, independence of hidden variables on the conducted experiments, and wave-particle objectivity we show that these ideas are incompatible with any theory, not only with quantum mechanics.

We review recent versions of the information paradox, framed in the context of the AdS/CFT correspondence. We describe how they can be resolved using "state dependent" bulk to boundary maps for the black hole interior in AdS/CFT. We argue that this feature is necessary not only for single sided black holes but also for the eternal black hole.

We resolve some potential ambiguities in this map. We extend this construction of the black hole interior to entangled systems and show how a version of the ER=EPR conjecture emerges naturally in this process. Finally, we comment on the possible semi-classical origins of state-dependence.

Astrophysical observations suggest that the majority of matter in the Universe is made up of novel Weakly Interacting Massive Particles (WIMPs).  Such WIMPs are often predicted by extensions to the Standard Model.  Efforts have been underway for more than two decades to detect WIMPs directly in detectors on earth.  The challenge is great because of the small energies involved and the low interaction rates. The field has been driven by progress in detectors able to identify radioactive backgrounds. I will review how recent enthusiasm for low-mass WIMPs, which was generated by tantalizing hints seen in several experiments, has waned.  Lastly, I will discuss various ideas to check the longstanding DAMA WIMP-detection claim, including the feasibility of alkali-halide cryogenic detectors.

Can we learn about New Physics with astronomical and astro-particle data? Understanding how this is possible is key to unraveling one of the most pressing mysteries at the interface of cosmology and particle physics: the fundamental, particle nature of the dark matter.
I will discuss some of the recent puzzling findings in astro-particle and astronomical observations that might be related to signals from dark matter. I will first review the status of explanations to the cosmic-ray positron excess, emphasizing how we might be able to discriminate between astrophysical sources and dark matter. 
I will then discuss the evidence for an X-ray line at 3.5 keV, and present new results on systematic effects and on the role of previously underestimated astrophysical lines.
Finally, I will discuss a reported excess of gamma rays from the central regions of the Galaxy.  I will address the question of whether we are possibly observing a signal from dark matter annihilation, how to test this hypothesis, and which astrophysical mechanisms constitute the relevant background.