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.