We will be hosting two visitors to our group, Michel Buck and Ian Jubb, who will give seminars on Monday afternoon (June 22). The talk will both be held in AP&M room 7421, at 1 pm (Michel Buck) and 2:30 pm (Ian Jubb).

Dr. Michel Buck

Northeastern University, Department of Physics

Title: An overview of causal sets

Abstract: Causal set theory is an approach to quantum gravity based on the idea that spacetime is fundamentally discrete and Lorentz invariant. Structurally, a causal set is a locally finite partial order, or a transitive DAG (directed acyclic graph). After a brief introduction to the idea, I will give an overview of some of the recent research activity in causal sets. Some topics I hope to touch on are: measures of discrete geometry (e.g. distance, curvature,…), dynamics on causal sets (e.g. classical and quantum fields), and phenomenology from causal sets (e.g. dark energy).

Ian Jubb

Imperial College London, Department of Physics

Title: Boundary Terms for Causal Sets

Abstract: In Causal Set theory the ordering of the spacetime “atoms” and their number are meant to give us all of the geometrical information. Thus, we should be able to construct causal set expressions that give us back particular geometrical quantities. In this talk I will describe a recent result that allows one to determine the Gibbons-Hawking-York (GHY) boundary term for a causal set. The GHY term appears in the action for a spacetime with a boundary, and is simply the integral over the extrinsic curvature of that boundary. A side effect of the work behind this result was the emergence of a new way to calculate the dimension of a causal set. Finally, I would like to discuss the boundary contributions that are “hidden” in the bulk action for a causal set.