I will discuss the Lorentzian quantum gravity path integral in simplicial approaches like Regge calculus and spin foams. I will draw connections between three different aspects of the Lorentzian path integral: firstly the appearance of light cone irregular configurations, which result in a surprising ambiguity for the Lorentzian path integral, secondly the fate of spike configurations in the...
The conceptual and computational progresses in the covariant framework of LQG have brought a number of results in its application to cosmology. In this talk I highlight some of the most interesting steps forward in spinfoam cosmology. I briefly review the general assumption in defining the cosmological model. I focus then on the development of a novel strategy to compute cosmological...
Based on the exact holographic duality formula related the Ponzano-Regge amplitudes for 3d quantum gravity and the 2d inhomogeneous Ising model, I will clarify the relation between bulk path integrals and boundary theory in the context of spinfoams. Through simple toy-models, I will explain how bulk observables become the coupling constants of the boundary theory, and vice-versa how the bulk...
Quantum gravitational tunneling effects are expected to give rise to a number of interesting observable phenomena, including, in particular, the evolution of black holes at the end of their existence. Covariant Loop Quantum Gravity provides a framework to study these phenomena, yet a precise identification of tunneling processes is still not known. Motivated by tunneling processes, I will...
Computing spin foam amplitudes explicitly is still a challenging task, in particular for 2-complexes consisting of multiple vertices. In this talk I will present three algorithms that will help construct and compute amplitudes more efficiently.
The first algorithm allows us to easily construct 2-complexes and the associated amplitude. We define the number of spin foam vertices and choose...
Are the atoms of space distinguishable? In this talk I discuss recent developments on the construction of a diffeomorphism invariant notion of entanglement entropy of a region in loop quantum gravity and spinfoams.
How complex is the structure of quantum geometry? In loop quantum gravity, atoms of space are SU(2) 4-valent intertwiners, which describe quantum tetrahedra. The complexity of this construction has a concrete consequence in recent efforts to simulate quantum geometry models and toward experimental demonstrations of quantum gravity effects. There is, then, a computational and an experimental...
To study the large-j asymptotics of Lorentzian spinfoam EPRL models on complex four dimensional geometries with internal points, it is crucial to first understand the underlying impact of geometrical structures on the spinfoam amplitudes, due to the existence of continuous critical points and their non-trivial contribution in the covariant path integral formalism. In this paper we propose...
Spin foams arose as the covariant (path integral) formulation of quantum gravity depicting transition amplitudes between different quantum geometry states. Though a lot of progress has been made in defining the underlying mathematics, actually calculating the corresponding amplitudes is still a challenging topic, especially for more complicated, thus more physically-relevant cases. Following...
The Barbero-Immirzi parameter appears in the EPRL spinfoam model via a duality rotation. In an effective field theory description, this duality rotation results in a relation between the coupling constants of parity-even and parity-odd higher-curvature terms. We study cosmic inflation in this effective theory and show that the observation of a primordial tensor polarization, together with the...
In this talk, we develop a quantum theory of homogeneously curved tetrahedron geometry, by applying the combinatorial quantization to the phase space of tetrahedron shapes defined in arXiv:1506.03053. Our method is based on the relation between this phase space and the moduli space of SU(2) flat connections on a 4-punctured sphere. The quantization results in the physical Hilbert space as the...
This talk reports on a recent proposal for a Lorentzian spin-foam coherent amplitude in 2+1 dimensions, defined for an arbitrary combination of space- and time-like edges. The construction makes use of a new set of boundary coherent states, derived from the correspondence between Majorana spinors and space-like 2+1 vectors. The amplitude is shown to recover the Lorentzian Regge action in the...
Area metrics generalize spacetime geometry based on lengths and provide a candidate parametrization of the extended configuration space of loop quantum gravity and spin foams in the semiclassical regime. On this basis, I will consider generally covariant actions to second order in area metric fluctuations and derivatives. The effective actions for the subset of area metric degrees of freedom...
Can one compute thermodynamic quantities, such as entropy, with a Lorentzian path integral? Using a regularization of the path integral via Regge calculus, we will see that the answer is affirmative.
Irregularities in the light cone structure, e.g. configurations with contractible closed timelike curves, play an essential role for this conclusion. Such light cone irregularities contribute...
We expect quantum field theories for matter to acquire intricate corrections due to their coupling to quantum fluctuations of the gravitational field. This can be precisely worked out in 3D quantum gravity: after integrating out quantum gravity, matter fields are effectively described as non-commutative quantum field theories, with quantum-deformed Lorentz symmetries. An open question...
