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The Lorentzian path sum in causal set theory(CST)  can be defined using the discrete EInstein-Hilbert or Benincasa-Dowker-Glaser(BDG)  action. It has been a long standing question  in CST whether  the path sum is  dominated by a class of non-continuum like layered posets — this would make it much harder to find a dynamically generated continuum approximation —  or whether the BDG action suppresses this contribution.  In this talk I will discuss a series of results that show that to  leading order in the saddle point approximation,  this dominating  class of layered posets is strongly suppressed. Moreover this is true for a  more general class of actions which include the BDG action.   We conclude with some remarks on the interpretation of these results and related  open questions. 

Zoom link:  https://pitp.zoom.us/j/91794153633?pwd=TTFnS0hpQ2s5eFVDM3k5ZDkxcndkUT09

In this mini course, I shall introduce the basic concepts in 2D topological orders by studying simple models of topological orders and then introduce topological quantum computing based on Fibonacci anyons. Here is the (not perfectly ordered) syllabus.                      

•        Overview of topological phases of matter
•        Z2 toric code model: the simplest model of 2D topological orders
•        Quick generalization to the quantum double model
•        Anyons, topological entanglement entropy, S and T matrices
•        Fusion and braiding of anyons: quantum dimensions, pentagon and hexagon identities
•        Fibonacci anyons
•        Topological quantum computing.

In this talk I will show the equivalence of several different tests of the Jacobi identity for celestial currents at tree level, in particular finding a simple, practical condition on hard momentum space 4-point amplitudes in any EFT. Along the way I will clarify the role of the order of soft and collinear limits in obstructing the Jacobi identity for soft insertions and I will argue that, despite their current-algebra-like properties, soft insertions as formulated in this talk cannot be interpreted as local operators in celestial conformal field theory.

Zoom link:  https://pitp.zoom.us/j/99642885302?pwd=dWZhbzZUYnBuSlJ3UzBhSHdqdzVKdz09