Seminar by David Garfinkle

Talk time and date:

Nov 11th at 11 AM in Nicholson 241

Title: Spikes in the approach to spacetime singularities

Abstract: As a spacetime singularity is approached spatial structures develop on a small and ever shrinking spatial scale.  These structures are called spikes.  This talk will cover analytic approximations of spikes, numerical simulations of spikes, and the possibility that spikes might be destroyed by the effects of quantum gravity.

Seminar by Marios Christodoulou

  Talk time and date:
  Nov 8th at 11:30 in Nicholson 241

Title: Complete Observable from covariant LQG: The Planck Star Tunneling time

Abstract: 

Covariant LQG provides the machinery to define probability amplitudes for transitions between 3D geometries via a path integral over interpolating quantum spacetimes. An astrophysically relevant probability is expected for the transition of a Black Hole to a White Hole geometry. The setup for this calculation provides a concrete example of how to use cov LQG and extract a complete observable from the theory and how to deal with the "problem of time".

 

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