LSUREL

Wednesday, March 18, 2020

Speaker: Alejandro Corichi, UNAM Morelia.

Place: Via Zoom.

Date: Thursday, March 19th.

Time: 10am

Title: TBA

Thursday, January 23, 2020

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.

Tuesday, November 19, 2019

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.

Group Seminar by Adrià Delhom I Latorre

Speaker: Adrià Delhom I Latorre
Place: 241 Nicholson

Date: Wednesday Nov 20th

Time: 13:30

Title: Curvature-based Metric-affine gravity

Abstract: I will give an overview of metric-affine gravity theories, focusing in those with actions built with the Ricci tensor, trying to emphasize the phenomenological aspects of these theories that are similar to those encountered in quantum gravity theories. First, I will review the different frameworks that fall within metric-affine gravity (teleparallel, gauge gravity, etc.). Focusing on actions built upon curvature tensors (curvature-based), I will then explain why low-curvature modifications to GR, that could explain the accelerated expansion, are ruled out by experiments. Then I will show why metric-affine higher order curvature theories can be free from ghosts and the role played by projective symmetry on this. After that, I will give some results involving black hole like objects that arise naturally in several metric-affine models are described by non-singular spacetimes (in the sense of geodeticall completeness). I will also present some bouncing cosmological models within these theories and how the LQC dynamics can be mimicked by an f(R) theory. Finally, I will show how in some curvature-based metric-affine gravity the matter sector develops non-linear interactions that can be used to constrain these theories.

Wednesday, November 13, 2019

Online seminar by Marcin Kisielowski

Speaker: Marcin Kisielowski

Place: 241 Nicholson

Date: Wednesday Nov 13th

Time: 11 AM

Title: Spin-foam model for gravity coupled to massless scalar field

Abstract: In my talk I will present a spin-foam model for gravity coupled to massless scalar field which we derived from the Canonical Loop Quantum Gravity. We generalized to the full theory the scheme first proposed in the context of Loop Quantum Cosmology by Ashtekar, Campiglia and Henderson, later developed by Henderson, Rovelli, Vidotto and Wilson-Ewing.