Plenary Abstracts

Florian Beyer

University of Otago

Guided tour through AVTD regions of the BKL world

In this talk, I discuss the concept of so-called AVTD solutions of Einstein's field equations and its relation to the BKL conjecture and strong cosmic censorship. After a review of the current state of knowledge, I talk about a new result by Ames, Isenberg, LeFloch and myself about the existence of a large family of smooth half-polarized T2-symmetric vacuum solutions with AVTD behavior. This result was obtained using a new Fuchsian existence theorem for quasilinear symmetric hyperbolic systems.

Richard Easther

University of Auckland

Gravitational Waves From The Early Universe

A variety of processes in the very early universe can generate a stochastic background of gravitational waves. These include fluctuations generated quantum mechanically during the inflationary epoch, and gravitational waves sourced by phase transitions or other nonlinear processes in the early universe. I will discuss these mechanisms and their potential to provide information on the physics of the primordial universe, and highlight the different experimental challenges they present.

Steve Maddox

University of Canterbury

Galaxy Surveys and Large-scale Structure in the Universe

Observations of the distribution of galaxies on large scales have been useful in determining cosmological parameters, the growth of density fluctuations in the universe, and the formation and evolution of galaxies. I will summarize the basic ideas and some recent work based on the Herschel ATLAS, a new sub-mm galaxy survey.

Andrew Melatos

University of Melbourne

Nuclear astrophysics with gravitational wave telescopes

Neutron stars are currently the only natural settings where one can study experimentally the fundamental physics of bulk nuclear matter in the true many-body limit. Gravitational waves in the hectohertz band will provide unprecedented opportunities to explore this physics by measuring directly the internal motions of neutron stars. In this review, examples are given of how gravitational-wave data can be inverted to infer the thermodynamic coefficients (e.g. compressibility, viscosity), state of superfluidity, and electrical properties (e.g. resistivity, state of magnetization) of nuclear matter. Astrophysical phenomena to be reviewed include rotational glitches in isolated pulsars and thermonuclear X-ray bursts in accreting neutron stars. Exciting new opportunities abound to do multi-messenger astronomy in these and many other areas, by combining radio, X-ray, and gravitational-wave data from current- and next-generation detectors.

Renate Meyer

University of Auckland

Markov chain Monte Carlo methods for Bayesian gravitational radiation data analysis

We give a review of Markov chain Monte Carlo (MCMC) techniques for estimating the physical parameters associated with a gravitational radiation signal. The techniques are applicable to gravitational radiation detectors that are ground based (such as LIGO) or space based (such as LISA) and have been applied to simulated signals of coalescing binary inspirals (black holes and/or neutron stars), rapidly rotating neutron stars and bursts. We briefly recall the Bayesian approach to statistical inference and illustrate simulation-based posterior computation. In many applications, the standard application of the basic Metropolis-Hastings algorithm or Gibbs sampler yields poor mixing. Thus, tuning algorithms to the specific problem becomes very important to speed up convergence. In many applications, only a combination of various different strategies for convergence acceleration yields an efficient sampling of the parameter space. We focus in particular on the problem of estimating parameters of gravitational wave burst signals from simulations of rotating stellar core collapse and bounce and outline our approach via a principal component analysis of signal waveforms that yields a random effects linear regression model. A MH-within-Gibbs routine can be used to efficiently sample from the posterior distribution. It is shown how the reconstructed signal and the eigenvector amplitude estimates provide information on the physical parameters associated with the core collapse event.

Todd Oliynyk

Monash University

Lagrange coordinates for the Einstein-Euler equations

Perfect fluid balls are used to model many different types of physical objects such as gaseous planets and stars. An important physical problem is to understand the evolution of these fluid balls. Due to the presence of a free boundary at the fluid vacuum interface, establishing existence and uniqueness of solutions is a difficult problem. In this talk, I will describe a new approach to this problem that is based on a symmetric hyperbolic formulation of the Einstein-Euler equations in Lagrange coordinates. Unlike previous formulations, the Lagrange coordinates are adapted to a vector formulation of the Euler equations due independently to J. Frauendiener and R.A. Walton. As I will show, the vector nature and geometric structure of the Frauendiener-Walton formulation makes it possible to exploit the diffeomorphism freedom available in order to fix Lagrange coordinates while retaining a symmetric hyperbolic form for the Einstein-Euler equations. Time permitting, I will also discuss two applications of these Lagrange coordinates. The first is to provide a geometric description of the zero shift and densitized lapse coordinate systems for the Einstein equations. The second is to establish the existence of solutions in 2 space time dimensions to the Euler equations with a physical vacuum.

Dan Shaddock

Australian National University

From LISA to GRACE: Space-based gravitational observations

The Gravity Recovery and Climate Experiment (GRACE) is a joint NASA German Space Agency mission to study key aspects of the Earth’s climate. Orbiting since 2002, GRACE uses precision measurements of gravity to produce maps of melting polar ice and changes in continental ground water. GRACE consists of twin satellites separated a few hundred kilometres in a polar, low-Earth orbit. A map of the Earth’s gravity field is inferred from micrometre-level changes in the satellites’ separation. NASA is planning on launching the GRACE Follow-On mission in 2016 in partnership with Germany. GRACE Follow-On will be almost identical to GRACE except that a laser ranging instrument is planned to augment the microwave ranging instrument. Derived largely from the gravitational wave detector technology of LIGO and LISA, this laser instrument should improve on the GRACE range measurement by a factor of 20. This talk will present GRACE science and technology, and provide an overview of the laser ranging instrument.

Rachel Webster

University of Melbourne

Microlensing Quasars

Gravitational microlensing is establishing itself as a powerful probe of quasar structure. In this talk, I will briefly discuss the observed differences between microlensing in the sparse regime and microlensing at high optical depths. The latter case, which is being explored in quasar studies, must be coupled with statistical studies based on modelling the emission regions. Several different approaches have proven successful in providing measurements of the geometric sizes of the emission regions. The current state of these studies will be described and the talk will conclude with a discussion of future prospects of this technique.