Speaker
Description
In this talk, I discuss recent advances in Lorentzian quantum cosmology using group field theory (GFT) condensate cosmology and effective spin foams.
First, in the GFT approach, I introduce the complete Barrett-Crane (cBC) TGFT model coupled to four scalar fields, establishing a connection between the causal character of quantum geometry and relational scalar clock and rods. This allows to derive relational cosmological perturbation equations from quantum entanglement between spacelike and timelike tetrahedra (discussed in detail in Luca Marchetti's talk).
Second, in the effective spin foam approach, I introduce Lorentzian frustum geometries for spatially flat, isotropic and homogeneous cosmology, addressing causality violations, scalar field coupling, and discrete dynamics. Following new results in (2+1)-dimensional Lorentzian spin foams (see José Diogo Simão's talk), we propose an effective spin foam model for (2+1)-dimensional quantum cosmology with a path integral measure derived from spin foams.
Overall, this talk epmhasizes the importance of timelike building blocks in quantum cosmology, advocating for models that incorporate a causally complete set of discrete Lorentzian geometries.