Talk by Roberto De Pietri

Title: The Physics of Binary Neutron Star mergers: the fate of the six galactic binary systems and the associate gravitational wave signal.

Time: 11:00 Wednesday November 9th 2016

Place: 241 Nicholson

The subject is a joint work with Frank Loeffler (A. Feo, R. De Pietri, F. Maione and F. Loeffler, Modeling Mergers of Known Galactic Systems of Binary Neutron Stars. arXiv:1608.02810.) as well as results from: (1) Classical and Quantum Gravity, 33, no. 17, 175009 (2016)arXiv:1605.03424.(2) Phys. Rev. D 93, 064047 arXiv:1509.08804.

Talk by Dr. Jonathan Blackman

Title: Surrogate models of gravitational waveforms from numerical relativity simulations of black hole mergers

Time: 11:00 Tuesday October 25 2016
Place: 241 Nicholson

Abstract:

GW150914 was the first detection of gravitational waves from a binary black hole merger, bringing us into the era of gravitational wave astronomy. From such gravitational wave detections, we can put constraints on deviations from general relativity (GR), as well as measure the masses and spins of the black holes involved in the merger. Such measurements require knowledge of the gravitational waveforms predicted by GR for all relevant masses and spins. Numerical relativity (NR) simulations are now sufficiently robust that we can accurately simulate binary black hole mergers and obtain the waveform for all but the most extreme parameters, but they are too computationally expensive for a dense coverage of the parameter space. The effective-one-body model and phenomenological waveform models agree well with NR for the parameters of GW150914, but could be insufficiently accurate for estimating the parameters of a loud gravitational wave detection in other regions of the parameter space. NR surrogate models attempt to rapidly and accurately interpolate the waveforms from a set of NR simulations over a subset of parameter space. Using the Spectral Einstein Code (SpEC), we have built NR surrogate models for non-spinning binaries with mass ratios up to 10, and for spinning precessing binaries with a restricted spin direction on the smaller black hole. They typically perform an order of magnitude better than other waveform models when compared to NR waveforms which were not included in the surrogate training set, and can be used in gravitational wave parameter estimation.

Talk by Guillermo Mena-Marugán

Title: 

Uniqueness of the quantization of Dirac fields with unitary dynamics

Time: Wednesday May 11th 11:00am
Place: 241 Nicholson

Talk by Brajesh Gupt

Title: Can inflation in closed FLRW model have observational imprints?

Abstract: We study gauge invariant perturbations in an inflationary FLRW universe with positive spatial curvature. The resulting two point function at the end of inflation shows suppression of power at large scales (corresponding to $\ell < 30$ at CMB). By comparing our results with the recent Planck data we revisit the constraints of spatial curvature and discuss the role of spatial curvature on the estimation of other cosmological parameters. We also highlight the main differences from the standard inflationary scenario in a flat FLRW model and potential implications for tensor modes, non-gaussianity and future observations.

Time: Wednesday April 27th 11:30am
Place: 241 Nicholson

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.