Seminar by Ivan Agulló

Speaker: Ivan Agulló, LSU

Place: The Cloud

Date: Thursday July 29th

Time: 12pm Central.

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Recorded lecture.

Title: Stimulated Hawking effect on an Optical White-Black Hole

Abstract:

In this informal talk I’ll summarize my recent work 2107.10217 with A. Brady and D. Kranas, on which we study the Hawking effect in optical systems containing the analog of a pair white-black hole. Our work contains a synergistic combination of analytical and numerical methods. Our analytical treatment is based on techniques from quantum Gaussian information, and it provides a simple and efficient model to describe all aspects of the out state, including the entanglement between any bi-partition. These tools allow us to analyze for the first time subtle aspects of the Hawking process, like the influence that ambient thermal noise and detector inefficiencies have on the out state. We find that aspects of the Hawking effect that are of quantum origin, i.e.\ quantum entanglement, are extremely fragile to the influence of inefficiencies and noise. More importantly, we propose a protocol to amplify and observe these quantum aspects, based on seeding the process with a single-mode squeezed input. Our ideas open the door to new possibilities of experimental verification of the Hawking effect.

Seminar by Francesco Sartini

 

Speaker: Francesco Sartini, ENS Lyon

Place: The Cloud

Date: Thursday July 22nd

Time: 12pm Central.

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https://lsu.zoom.us/j/6574388959

Title: Black Hole interior: Symmetries and regularization

Abstract:

The spacetime in the interior of a black hole can be described by an homogeneous line element, for which the Einstein–Hilbert action reduces to a one-dimensional mechanical model. We have shown that this model exhibits a symmetry under the (2+1)-dimensional Poincaré group. The existence of this symmetry provides a powerful criterion to discriminate between different regularization and quantization schemes. It also unravels new aspects of symmetry for black holes, and opens the way towards a rigorous group quantization of the interior. Remarkably, the physical ISO(2,1) symmetry can be seen as a broken infinite-dimensional symmetry. This is done by reinterpreting the action for the model as a geometric action for the BMS3 group, where the configuration space variables are elements of the algebra bms3 and the equations of motion transform as coadjoint vectors.

Seminar by Hongguang Liu

Speaker: Honggang Liu, FAU Erlangen

Place: The Cloud

Date: Thursday January 14th

Time: 12pm Central.

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https://lsu.zoom.us/j/96989058282

Title: Improved Effective Dynamics of Loop-Quantum-Gravity Black Hole and Nariai Limit

Abstract: We propose a new model of the spherical symmetric quantum black hole in the reduced phase space formulation. We deparametrize gravity by coupling to the Gaussian dust which provides the material coordinates. The foliation by dust coordinates covers both the interior and exterior of the black hole. After the spherical symmetry reduction, our model is a 1+1 dimensional field theory containing infinitely many degrees of freedom. The effective dynamics of the quantum black hole is generated by an improved physical Hamiltonian 𝐇 where the holonomy correction is implemented by the 𝜇-bar-scheme regularization with a Planckian area scale Δ (which often chosen as the minimal area gap in Loop Quantum Gravity). The effective dynamics recovers the semiclassical Schwarzschild geometry at low curvature regime and resolves the black hole singularity with Planckian curvature. Our model predicts that the evolution of the black hole at late time reaches the charged Nariai geometry dS2xS2 with Planckian radii. The Nariai geometry is stable under linear perturbations but may be unstable by nonperturbative quantum effects. Our model suggests the existence of quantum tunneling of the Nariai geometry and a scenario of black-hole-to-white-hole transition. During the transition, the linear perturbations exhibit chaotic dynamics with Lyapunov exponent 𝜆=2𝜋𝑇∼1/Δ relating to the Hawking temperature T of dS2. In addition, the Nariai geometry in our model provides an interesting example of Wheeler's bag of gold and contains infinitely many infrared soft modes with zero energy density. These infrared modes span a Hilbert space carrying a representation of 1-dimensional spatial diffeomorphisms (or the Witt/Virasoro algebra). The spatial diffeomorphisms are conserved charges of the effective dynamics by 𝐇.

Seminar by Anupam Mazumdar

 

Speaker: Anupam Mazumdar, University of Groningen
Place: The Cloud

Date: Tuesday, December 15th

Time: 9am

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https://lsu.zoom.us/j/6574388959?pwd=UlVxUzYrUHMvSW1GVUswSjVJc2I0QT09

Title: Witnessing Quantum gravity in a laboratory via miniaturist quantum accelerator

Abstract: Unveiling the nature of spacetime remains one of the final frontiers of modern theoretical physics. I will discuss how to witness the quantum nature of gravity in a table-top experiment by creating the right witness involving the two neutral masses (spin embedded) undergoing through the Stern-Gerlach apparatus. I will discuss various challenges involved in pursuing the dream of witnessing graviton and the critical challenges. There are many challenges to be met and I will discuss the important ones: (1)  To create a macroscopic quantum superposition of heavy masses via the Stern-Gerlach setup while controlling the stray gravitational acceleration and the gravity gradient noise, (2) Precise constraints on the magnetic field/current such that various electromagnetic interactions are under control, (3) Vacuum dominated Casimir effect which will create the main background for the experiment, (4) Constraints on vacuum and temperatures, (5) Feasibility of the experiment in a drop-tower, (6) The material properties and patch potentials. I will briefly discuss time scales for realising such an accelerator which will witness for the first time the graviton in a terrestrial laboratory.

Audio+Slides of the talk (.mp4) (500mb)

Subtitles (.vtt) (80kb)

Speaker: Alejandro Corichi, UNAM Morelia.

Place: Via Zoom.

Date: Thursday, March 19th.

Time: 10am

Title: TBA

Group seminar by Jorge Pullin

Speaker: Jorge Pullin
Place: Digital Media Theater

Date: Thursday, January 9th

Time: 3:30pm

Title: Universality and scaling in the collapse of spherical scalar fields in semiclassical loop quantum gravity.

Group Seminar by Susanne Schander

Speaker: Susanne SchanderPlace: 241 Nicholson

Date: Wednesday Nov 19th

Time: 13:30

Title: Backreactions in Quantum Cosmological Perturbation Theory

Abstract:

Cosmological perturbation theory has a long tradition for describing the early phases of the Universe. As the observations of the CMB radiation suggest, it is reasonable, at least as a first approximation, to implement cosmological inhomogeneities as small perturbations around homogeneous and isotropic FRW solutions. In these approaches, backreactions between the inhomogeneities and the background are usually neglected. There is an ongoing debate about how and to which extend these backreactions affect the large scale structure of the Universe. Even at a purely classical level, there is no conclusive answer to this question yet.

In my talk, I am going to present a new systematic formalism for implementing backreactions in cosmological perturbation theory, in which both, the perturbations and the homogeneous degrees of freedom are considered as quantum degrees of freedom. As a more realistic theory of quantum fields on quantum cosmological space times, it can help to close the gap between a full theory of quantum gravity and symmetry-reduced models of quantum cosmology, and to confront these theories with observations. Our results show that quantum backreactions imply non-trivial corrections that are potentially phenomenologically significant.