Transformation Groups Seminar

Speaker: Stephen Theriault (University of Southampton)

"Polyhedral products for connected sums of simplicial complexes"

Time: 09:30

Room: https://westernuniversity.zoom.us/s/93798234275, Passcode: 520011

We investigate how the homotopy type of a polyhedral product changes under the operation of taking the connected sum of two simplicial complexes. This is obtained as a consequence of a more general result that considers how the homotopy type of a polyhedral products changes under the operation of gluing two simplicial complexes together along a common full subcomplex.

Colloquium

Speaker: Muxin Han (Florida Atlantic University)

" Four-dimensional Spinfoam Quantum Gravity with Cosmological Constant"

Time: 15:30

Room: MC 107

We present a formulation of 4-dimensional Lorentzian spinfoam quantum gravity with cosmological constant. The construction of spinfoam amplitudes uses the state-integral model of PSL(2,C) Chern-Simons theory and the implementation of simplicity constraint. The formulation has 2 key features: (1) spinfoam amplitudes are all finite, and (2) With suitable boundary data, the semiclassical asymptotics of the vertex amplitude has two oscillatory terms, with phase plus or minus the 4-dimensional Lorentzian Regge action with cosmological constant for the constant curvature 4-simplex.