Talk by Jorge Pullin

Title: Conformal loop quantum gravity: first steps
Time: Thursday April 7th 12:30pm
Place: 241 Nicholson

Talk by Dr. Mercedes Martin Benito

Speaker: Dr. Mercedes Matín-Benito, Radboud University, 

Title: Uniqueness of the Fock representation of Dirac fields in closed FRW cosmology.

Time: 11:00 Wednesday Nov 18 2015
Place: 241 Nicholson

Abstract:

I will discuss about the ambiguity that exists in the Fock quantization of free fields in curved spacetimes, and how to employ physically motivated criteria to fix such ambiguity and thus select a privileged Fock representation. In the familiar case of Fock quantization of free fields in Minkowski, demanding Poincaré invariance fixes the vacuum and therefore the Fock representation. In contrast, in non-stationary situations we cannot longer demand time-translation invariance to select the vacuum of the representation. We can still ask for invariance under the group of spatial isometries of the background, but in general this criterion is not enough to remove the ambiguity in the representation. Then a natural question arises: can we demand extra criteria to select a privileged vacuum? In turns out that in certain non-stationary spacetimes, such as compact cosmological spacetimes, the answer is in the affirmative: Demanding a unitary implementation of the dynamics in the quantum theory serves to select a unique (up to unitary equivalence) Fock representation. I will illustrate this fact in the particular case of a Dirac field propagating in a homogeneous and isotropic spacetime with the spatial sections given by three-spheres.

Talk by Dr. V. Sreenath, LSU

Talk by Dr. V. Sreenath

Speaker: Dr. V. Sreenath, LSU

Title: Computation and characteristics of inflationary three-point functions
Time: 11:00 Wednesday August 26 2015
Place: 241 Nicholson

Abstract:

In this talk, divided into two parts, I shall describe our efforts to numerically evaluate the inflationary three-point functions (which evidently include, apart from the oft-considered scalar bi-spectrum, the cross-correlations involving scalars and tensors as well as the tensor bi-spectrum), and also discuss the consistency relations obeyed by all the three-point functions. In the first part of the talk, I shall outline the numerical procedure we have constructed, based on the Maldacena formalism, to compute the three-point functions in single field inflationary models involving the canonical scalar field. After introducing dimensionless non-Gaussianity parameters to characterize the scalar-tensor cross-correlations, I shall utilize the numerical code to study the behavior of non-Gaussianity parameters describing all the three-point functions in three types of inflationary models which contain departures from slow roll and lead to power spectra with features that result in an

improved fit to the CMB data. In the second part of the talk, following a sketch of the derivation of the consistency relations, I shall express the consistency relations in terms of the non-Gaussianity parameters and explicitly examine (analytically as well as numerically) the validity of these relations away from slow roll. I shall illustrate that the consistency conditions hold true even in scenarios consisting of strong departures from slow roll.

Talk by Dr. Edward Wilson-Ewing

Speaker: Dr. Edward Wilson-Ewing, Albert Einstein Institute
Title: Loop Quantum Cosmology with Self-Dual Variables
Time: 11:00 Wednesday May 27 2015
Place: 241 Nicholson

Abstract:

I will present some recent results on a loop quantization of the closed Friedmann universe using the complex-valued self-dual Ashtekar variables.  In particular, I will explain in detail how the reality conditions are imposed via the choice of the inner product, and also of the need to introduce a family of generalized holonomies in the quantum theory.  I will end by comparing the resulting quantum theory with standard loop quantum cosmology.

Talk by Prof. Emil Mottola

Speaker: Prof. Emil Mottola, Theoretical Division, Los Alamos National Laboratory. 
Title: Instability of de Sitter Space, the Schwinger effect and Dynamical Dark energy

Date: Wednesday December 3rd
Time: 11am
Place: Room 241 Nicholson

Global de Sitter space is unstable to particle creation. The O(4, 1) de Sitter invariant state is a 
de finite phase coherent superposition of particle and anti-particle solutions in both the asymptotic 
past and future, and therefore is not a true vacuum state. In the closely analogous case of a constant, 
uniform electric field, a time symmetric state analogous to the de Sitter invariant one is constructed, 
which is also not a stable vacuum state, because of the Schwinger effect. The role of a quantum anomaly
in the growth of perturbations and symmetry breaking is emphasized in both cases. Consequences
of this result for cosmology and the problem of vacuum dark energy will be discussed.

Talk by Suzanne Lanery

Speaker: Suzanne Lanery, Friedrich Alexander Universitaet, Erlangen.
Title: Extending the phase space of loop quantum gravity
Date: Monday December 1st
Time: 3pm
Place: Room 241 Nicholson

Abstract: Instead of formulating the state space of a quantum field theory over a single big Hilbert space, it has been proposed by Jerzy Kijowski to describe quantum states as projective families of density matrices over a collection of smaller, simpler Hilbert spaces. I will discuss the physical motivations for this approach and explain how it can be implemented in the context of LQG. While the resulting state space forms a natural extension of the Ashtekar-Lewandowski Hilbert space, it treats position and momentum variables on equal footing. This paves the way for the construction of semi-classical states beyond fixed graph level, and eventually for the derivation of symmetry reduced models from full LQG.

Talk by Cohl Furey

Date: Monday, November 24th 2014
Time: 3pm
Place: 241 Nicholson
Speaker: Cohl Furey, Perimeter Institute

Title:  Charge quantization from a number operator

Abstract:

Here, we explain how an unexpected algebraic structure, the division algebras, can be seen to underlie a generation of quarks and leptons.  From this new vantage point, electrons and quarks are simply excitations from the neutrino, which formally plays the role of a vacuum state.

Using the ladder operators which exist within the system, we build a number operator in the usual way. It turns out that this number operator, divided by 3, mirrors the behaviour of electric charge. As a result, we see that electric charge is quantized because number operators can only take on integer values.

Finally, we show a simple hermitian form, which leads uniquely to the nine generators of SUc(3) and Uem(1). This gives a direct route to the two unbroken gauge symmetries of the standard model.