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.

Talk by Barry Wardell (Cornell & UCD)

Title: Self-force via worldline integration: from extreme mass ratio inspirals to
cosmic strings
Time: Wednesday, September 10th, 11am
Place: 241 Nicholson

Abstract:
Of the potential sources of gravitational waves, two of the most fascinating
candidates are compact-object binary systems and cosmic strings. Binary
systems typically involve a pair of neutron stars or black holes inspiralling and coalescing to produce a single remnant. On the other hand, cosmic strings are a generic feature predicted by a large number of cosmological models and fundamental physics; like binary systems their existence is expected to generate large amounts of gravitational radiation.

Although these two phenomena are quite distinct in their origins and physical features, both can be modelled using closely related techniques. This talk presents a novel approach to both problems which combines new numerical and analytical methods and yields geometrical insight into the contributions to self-interaction from curved geometry (back-scattering) and trapping of null geodesics.

Talk by Ivan Agullo

Talk by Ivan Agullo

Title: Electromagnetic duality in QFT in curved space-time
Time: Tuesday July 8th 11am
Place: 241 Nicholson

Talk by Jorge Pullin

Title: The Casimir effect on a quantum spacetime
Time: Tuesday July 8th 3pm
Place: 241 Nicholson

Talk by Richard Price

Title: Black Hole Plunges; Understanding What the Computers Tell Us
Time: Monday July 7th 2014, 3pm
Place: 241 Nicholson

Talk by Brajesh Gupt

Title: Some numerical and phenomenological studies in loop quantum cosmology
Time: Monday June 23 2014
Place: 241 Nicholson

Abstract:
A key feature of the singularity resolution in loop quantum cosmology (LQC) is the occurrence of the quantum bounce when the spacetime curvature becomes comparable to the Planck scale. The presence of quantum bounce greatly modifies the dynamics of the early universe and can have important implications for the observational signatures. Although the quantum bounce has been previously studied via numerical methods for initial conditions that correspond to large macroscopic universes at late times, a detailed study of the robustness of the quantum bounce for a generic class of initial condition has so far been missing due to severe computational challenges. I will talk about a numerical scheme, Chimera, which we have developed to tackle these computational challenges. I will also discuss some phenomenological implications on the quantum bounce in anisotropic spacetimes.

Talk by Brajesh Gupt (LSU)

Title: Non-singular AdS-dS transitions in a landscape scenario
Time: Wednesday April 2
Place: 241 Nicholson

Abstract:
In the multiverse scanario allowing eternal inflation, it is an important problem to understand transitions between different vacua, of which the ones from anti-deSitter to de-Sitter is forbidden in the classical theory. In this talk, we consider toy landscape potentials: a double well and a triple well potential allowing anti-deSitter and de-Sitter vacua, in the effective dynamics of loop quantum cosmology for the k
=−1 FRW model. We show that due to the non-perturbative quantum gravity effects as understood in loop quantum cosmology, non-singular anti-deSitter to de-Sitter transitions are possible. In the future evolution, an anti-deSitter bubble universe does not encounter a big crunch singularity but undergoes a big bounce occurring at a scale determined by the underlying quantum geometry. These non-singular transitions provide a mechanism through which a probe or a ``watcher,'' used to define a local measure, can safely evolve through the bounce and geodesics can be smoothly extended from anti-deSitter to de-Sitter vacua.

Talk by Anton Joe (LSU)

Title: Effective dynamics of Kantowski-Sachs spacetime in loop quantum cosmology
Time: Wednesday April 2
Place: 241 Nicholson

Abstract:
We study singularity resolution in Kantowski-Sachs spacetime in the effective loop quantum cosmology setting for various matter models such as dust, radiation, cosmic strings, cosmological constant and scalar fields. We find the inverse triad correction and bounds on energy density, shear scalar and expansion scalar. The evolution of universe after bounce is studied and found that a Nariai-like spacetime is obtained for different choices of matter. We analyze the stability of these quantum Nariai-like spacetimes with respect to homogeneous perturbations and find that unlike classical Nariai spacetimes, these are stable.