This series consists of talks in the area of Quantum Gravity.
A burst of gravitational radiation passing through an arrangement of freely falling test masses far from the source will cause a permanent displacement of the masses, called the ''gravitational memory''. It has recently been found that this memory is closely related to the change in the so called ''super-translation'' charge carried by the spacetime, where ''super-translations'' here refer to an unexpected enlargement of the asymptotic symmetries of general relativity beyond the expected asymptotic Poincare-transformations, known already since the work of Bondi et al.
I will discuss the possibilities to mimic black hole physics in fluid flows. The starting point is an analogy discovered by Unruh between the propagation of sound in a flowing fluid and waves around a black hole. In these analog setups, it is possible to test various black hole effects, and challenge their robustness. In a recent water wave experiment, we have shown how to exploit this analogy to observe superradiant scattering, that is, the amplification of waves by extraction of angular momentum from a rotating flow.
In this talk I will discuss the SYK model from a quantum field theoretical perspective and present an i epsilon prescription which regularizes the divergences of the model.
I will talk about the relation between non-local theories and gravity. The main thesis is that non-local field theories naturally induce gravity, even at the classical level. Supporting this idea, I will study bi-local scalar field theories, which involve minimal deviations from locality. We will treat them both, bi-local theories and gravity perturbatively. We will see that bi-local theories encode gravity together with higher spin fields.
I will discuss the role(s) of the Immirzi parameter in Loop Quantum Gravity, insisting on the Poisson algebra formed by Thiemann's complexifier, the volume and the Hamiltonian constraint. In particular, we will see how loop quantum cosmology is a direct quantization of this CVH Poisson algebra and how cosmological evolution amounts to a flow in the Immirzi parameter.
In this talk, I will discuss the asymptotic safety paradigm, and will highlight that it can provide a framework for a predictive ultraviolet completion for gravity and matter. Specifically, I will discuss compelling hints that exist for the realization of asymptotic safety in pure gravity, and will then present recent progress on the case of gravity coupled to Standard Model matter.
I will explain how cosmological dynamics emerge from the hydrodynamics of isotropic group field theory condensate states in the Gross-Pitaevskii approximation. The correct Friedmann equations are recovered in the classical limit for some choices of the parameters in the action for the group field theory, and quantum gravity corrections arise in the high-curvature regime causing a bounce which generically resolves the big-bang and big-crunch singularities.
By applying loop quantum gravity techniques to 2+1 gravity with a positive cosmological constant Λ, we show how the local gauge symmetry of the theory encoded in the constraint algebra acquires the quantum group structure of SOq(4). By means of an Inonu-Wigner contraction of the quantum group bi-algebra we obtain the kappa-Poincaré algebra of the flat quantum space-time symmetries.
In this talk we present the study of canonical gravity in finite regions for which we introduce a generalisation of the Gibbons-Hawking boundary term including the Immirzi parameter. We study the canonical formulation on a spacelike hypersuface with a boundary sphere and show how the presence of this term leads to a new type of degrees of freedom coming from the restoration of the gauge and diffeomorphism symmetry at the boundary. In the presence of a loop quantum gravity state, these boundary degrees of freedom localize along a set of punctures on the boundary sphere.