This series consists of talks in the area of Quantum Gravity.
The entanglement entropy, while being under the spotlight of theoretical physics for more than ten years now, remains very challenging to compute, even in free quantum field theories, and a number of issues are yet to be explored.
I will discuss a proposed mechanism to fix the value of the top quark mass from asymptotic safety of gravity and matter, and will review the status of the proposal.
In this talk I will discuss several recent advances in loop quantum cosmology and its extension to inhomogeneous models. I will focus on spherically symmetric spacetimes and Gowdy cosmologies with local rotational symmetry in vacuum. I will discuss how to implement a quantum Hamiltonian evolution on these quantizations. Then, I will focus on how we can extract predictions from those quantum geometries, and finally analyze a concrete example: cosmological perturbations on Bianchi I spacetimes in LQC.
I suggest a minimal practical formal structure for a more fundamental theory than the Standard Model + GR and review a mechanism that produces such a structure. The proposed mechanism has possibilities of producing non-canonical phenomena in SU(2) and SU(3) gauge theories which might allow conditional predictions that can be tested.
The slides and other writings are posted on my web page
http://www.physics.rutgers.edu/~friedan/#Perimeter
The Bondi mass loss formula has been central in the context of early research on gravitational waves. We show how it can be understood as a particular case of BMS current algebra and discuss the associated central extension. We then move down to three dimensions where a more complete picture emerges.
Canonical quantization schemes often suggest modifications to classical dynamics, such as in an effective Friedmann equation. However, although often ignored, they also necessarily imply new effects for quantum space-time leading to new (quantum) symmetries. The invariant line-element, corresponding to new geometrical structures emerging in the presence of holonomy modifications in loop quantum gravity, shall be consistently derived in this talk. We shall use black-hole models to illustrate new features of this quantum space-time, going beyond standard Riemannian manifolds.
In the first part of the talk, I will describe the new large N limit of tensor models, based on the “index” of graphs (in contrast to the standard large N expansion based on the “degree”), and the associated new large D limit of matrix models. This new limit sheds an interesting light on the relation between disordered models à la SYK, tensor models and black holes. In the second part of the talk, I will apply these ideas to discuss the phase diagrams of some strongly coupled matrix quantum mechanics.
In this talk, I will summarize the status of the numerical evaluation of spin foam amplitudes focusing on the Lorentzian EPRL-FK model. I will illustrate how numerical methods can lift some limitations of the theory helping us understand better its continuum and semi-classical limit.
We argue that in quantum gravity there is no stable equilibrium state corresponding to the Born rule. Our main argument rests on the continued controversy over the physical meaning of the Wheeler-DeWitt equation. We suggest that attempts to interpret it are hampered by the conventional assumption that probabilities should be governed by a fixed Born rule. It is possible to abandon this assumption in a de Broglie-Bohm interpretation.
Singularities, boundary points of spacetime beyond which no extension is possible, continue to intrigue both mathematicians and physicists since they are places where our current understanding of physical law breaks down. The question of whether they exist in physical situations is still an open one. Fifty years ago, Hawking and Penrose developed the first general model independent singularity theorems. These theorems showed that singularities have to exist in any spacetime that satisfies certain properties.