ACGRG 10Welcome reception Monday 9 December from 16:30 to 18:30 in the Te Toki a Rata foyer. See the map (note: North is not on top in this map). The building is on Kelburn parade and can easily be reached with the local bus lines 18e, 21, 22, and 37. All other lectures/workshop will take place either in the Te Toki a Rata foyer, or in Te Toki a Rata lecture theatre 1 (TTRLT1). The conference and the teachers' workshop will take place in the Te Toki a Rata lecture theatre 1 (TTRLT1) at the Kelburn Campus. Welcome reception, morning and afternoon tea will be in the adjoining foyer. See the map (note: North is not on top in this map). The building is on Kelburn parade and can easily be reached with the local bus lines 18e, 21, 22, and 37.
ProgramFrom Tuesday to Thursday, the ACGRG10 conference takes place. On Friday, there will be a workshop for highschool teachers.
|Monday, 9/12||Tuesday, 10/12||Wednesday, 11/12||Thursday, 12/12||Friday, 13/12|
|5:00pm||Welcome Reception||ASGRG BGM|
Abstracts for ACGRG10
- Malcolm Anderson (Universiti Brunei Darussalam): Hypersurface Averages in Perturbed FLRW Cosmologies — Thursday, 12:00pm
The analysis of the effects of stochastic perturbations on a general FLRW space-time is complicated by the fact that the evolution of a fluctuation mean must be represented as a sequence of averages over a foliation of space-like hypersurfaces in the perturbed space-time, and there are many such choices of foliations. Furthermore, a correction can normally be evaluated only after each foliating hypersurface has been matched to a constant-time hypersurface in the FLRW background, and again there is no unique way of doing this.
In this talk I will discuss how both these difficulties can be resolved. The issue of hypersurface identification can be circumvented by indexing the foliation with the hypersurface average of a second observable - which would ideally be the redshift (although this is technically challenging). And I will argue that there are good physical reasons for choosing the hypersurfaces themselves to be co-moving with the cosmic fluid, in a sense which can be made mathematically rigorous. Within this framework, it is possible to classify a wide range of second-order corrections that have been proposed over the last 20 years.
- Estelle Asmodelle (University of Queensland): Dihedrally Opposed Orthogonal 4D Representation of Minkowski Spacetime — Wednesday, 11:30am
It is generally believed that 4D graphing of orthogonal axes is not possible. However, in this paper, I present a new, novel and simple graphical method for representing 4-Dimensional [4D] space or 4D Minkowski spacetime to facilitate a compact and comprehensive conceptual model. This is more than a pedagogic analysis, for it provides a framework for opposing orthogonal 4D graphical representation of special relativity. The geometric concept could later be expanded into curved spacetime for a graphical model of general relativity as well. The plotting of a 4D coordinate system is measured relative to the standard Cartesian coordinate system is achieved by employing the shear factor ξ. This method plots x1, x2, x3 and x4 onto x, y, and z axes producing a structure by the intersection of 4-planes, being a combination of pentahedrons sections. Minkowski spacetime diagrams and other 4D structures are mapped in this manner. Heuristically, this method also provides new insights into the spacetime lightcone structure and boundary, such that aspects of the 4D lightcone. The most significant pedagogical contribution is that this method proves a practical and simple methodology for students to visually conceptualise some aspects of 4D flat spacetime.
- Krzysztof Bolejko (University of Tasmania): Searching for non-Riemannian signatures in cosmological data — Thursday, 9:00am
The Einstein's theory of gravity, General Relativity (GR) was build on the theory of Special Relativity. This generalisation required utilising the full generality of the Riemannian geometry. Over the last 100 year, GR has successfully passed all observational tests. Currently, a number of tests are based on using the cosmological data to test GR. However, many of the present-day cosmological tests of GR are still based on the assumption of the Riemannian geometry. In order to fully study and test various extensions of GR one is also required to move beyond the Riemannian geometry. In my talk I will focus on light propagation and discuss what signatures in cosmological observational data could point to non-Riemannian effects. This talk will not be a comprehensive review of the issue — it will only focus on the distance and redshift relations. I will discuss "Litmus test"-type signatures which should not be observed if the geometry of the Universe is Riemannian. I will discuss observational constraints and talk how future surveys could provide a better insight into the underlying geometry of our Universe.
- Shon Shachar Boublil (University of Western Australia and Einstein-First project): Building and Teaching an Einsteinian Physics curriculum in WA — Thursday, 3:30pm
Einsteinian physics encompasses ideas of quantum mechanics and General relativity. This includes the geometry of curved spaces, universality of the speed of light, gravity, wave-particle nature of matter and radiation, quantisation, the intrinsic quantum statistical nature of all physical measurements, and applications of Einsteinian physics in the modern world. Despite the enormous impact of Einsteinian physics in many important aspects of human endeavour, the science taught in primary and secondary schools worldwide are based on 19th century Newtonian concepts. The Einstein-First project aims to test and evaluate learning progressions of modern physics through primary and secondary school. This project will sequence, integrate and test research-informed teaching and learning materials.
- Hristu Culetu (Ovidius University): Accelerating anisotropic fluid — Cancelled
- Jörg Frauendiener (University of Otago): The Sagnac effect in General Relativity — Wednesday, 12:00pm
The Sagnac effect can be described as the difference in travel time between two photons traveling along the same path in opposite directions. In this talk we explore the consequences of this characterisation in the context of General Relativity. We derive a general expression for this time difference in an arbitrary space-time for arbitrary paths. In general, this formula is not very useful since it involves solving a differential equation along the path. However, we also present special cases where a closed form expression for the time difference can be given. We discuss the effect in a small neighbourhood of an arbitrarily moving observer in their arbitrarily rotating reference frame. We also discuss the special case of stationary space-times and point out the relationship between the Sagnac effect and Fizeau’s “aether-drag” experiment.
- Maria Eugenia Gabach Clement (Universidad Nacional de Cordoba): Quasilocal quantities in General Relativity — Wednesday, 9:00am
In this talk we discuss the use of quasilocal quantities in General Relativity, mainly quasilocal mass, angular momentum and center of mass of a physical system.
We focus on the proposal by Chen, Wang and Yau and explore several aspects, like the relation to other definitions, meanings and applications to the geometrical inequalities problem.
- Michael Good (Nazarbayev University): Remnant-free Moving Mirror Model of Black Hole Radiation Field — Cancelled
- Jörg Hennig (University of Otago): Solitons and Black Holes — Tuesday, 9:00am
Among the vast number of nonlinear PDEs, a few belong to the remarkable class of integrable (soliton) equations. Examples include the Korteweg–de Vries (KdV) equation, the Sine-Gordon equation and the Ernst equation(s) in general relativity. After a brief history of solitons ("waves of translation"), we will see how nonlinear soliton equations are related to linear matrix problems and how this can be used to study properties of the solutions and to obtain exact solutions. In particular, we consider Bäcklund transformations and Riemann-Hilbert techniques. Then we look at a number of applications to general relativistic black hole spacetimes, including a constructive uniqueness proof of the Kerr solution, the balance problem for two black holes and a black hole area product formula.
- David Kofron (Charles University): Point particles and Appell's solutions on the axis of Kerr black hole for arbitrary spin in terms of the Debye potentials — Tuesday, 11:00am
The Teukolsky master equation — fundamental equation for test fields of any spin, or perturbations, in type D spacetimes — is usually treated in its separated form in analytical calculations. Then the solutions representing even the simplest sources — point particles — are expressed in terms of series. The only known exception is a static particle (charge or mass) in the vicinity of Schwarzschild black hole.
We present a generalization of this result to a static point particle of arbitrary spin at the axis of Kerr black hole. A simple algebraic formula for the Debye potential from which all the NP components of the field under consideration can be generated is written down.
Later, we focus on the electromagnetic field and employ the old Appell's trick to get so called electromagnetic magic field on the Kerr background.
We also show that a static electric point charge above the Kerr black hole induces, except an expected electric monopole, also a magnetic monopole charge on the black hole itself. This contribution has to be compensated.
On a general level we show that any solution of Teukolsky equation can serve as a Debye potential for field of the same spin and vice versa. We also discuss the Teukolsky–Starobinsky identities.
- Woei Chet Lim (Waikato University): Monotonic functions in Bianchi models with a scalar field — Tuesday, 3:00pm
The dynamics of Bianchi models are described by a system of ODEs. Qualitative results such as attractors can be obtained. The Hamiltonian provides a natural monotonic function that may be helpful in isolating the attractors. I will illustrate this with examples, and point out the limitations of this method.
- Francisco Lobo (University of Lisbon): Generalized curvature-matter couplings in modified gravity — Wednesday, 10:30am
In this talk, we review a plethora of modified theories of gravity with generalized curvature-matter couplings. The explicit non-minimal couplings, for instance, between an arbitrary function of the scalar curvature and the Lagrangian density of matter, induces a non-vanishing covariant derivative of the energy-momentum tensor, implying non-geodesic motion and consequently leads to the appearance of an extra force. Applied to the cosmological context, these curvature-matter couplings lead to interesting phenomenology, where one can obtain a unified description of the cosmological epochs. We also consider the possibility that the behavior of the galactic flat rotation curves can be explained in the framework of the curvature-matter coupling models, where the extra-terms in the gravitational field equations modify the equations of motion of test particles, and induce a supplementary gravitational interaction. In addition to this, these models are extremely useful for describing dark energy-dark matter interactions, and for explaining the late-time cosmic acceleration.
- Morgan Lynch (Technion — Israel Institute of Technology): Experimental Evidence for the Unruh Effect — Cancelled
- Colin MacLaurin (University of Queensland): Observer-dependent length-measurement in curved spacetime — Wednesday, 11:00am
I present a formalism for length measurement within a specified reference frame in curved spacetime. It compares a measurement direction (“ruler”) within a given observer’s local 3-space, to an extrinsic standard: either a coordinate gradient or another ruler. This complements the usual emphasis on intrinsic standards, such as the expansion tensor of a congruence. One illustration is in Schwarzschild spacetime, for which only specific cases have been previously considered (Gautreau & Hoffmann 1978).
The motivation is foundational understanding of GR. The formalism locates extended objects within arbitrary foliations of spacetime. Possible applications include averaging in cosmology, quantum mechanics on arbitrary foliations, or thermodynamics of black hole volumes. Surprisingly, the material does not appear even in monographs on measurement and spacetime splitting (Bini & de Felice 2010; Jantzen+ 2013).
- Muhammad Zubair Ali Moughal (Waikato University): Generating spiky solutions of Einstein field equations with the Stephani transformation — Tuesday, 3:30pm
In general relativity, the dynamics of spacetime is described by the Einstein field equations, which are a set of partial differential equations. The Stephani transformation is a solution-generating transformation and may generate spiky solutions. Most spiky solutions generated so far form spikes at early times.
In this talk, I present a solution that forms spikes at late times.
- Adrian Ottewill (University College Dublin): The Black Hole Perturbation Toolkit — Tuesday, 10:30am
I will provide an introduction to the Black Hole Perturbation Toolkit, an open software initiative that brings together software and data relating to black hole perturbation theory. These can then be used to model gravitational radiation from small mass-ratio binaries as well as from the ringdown of black holes. The former are key sources for the future space-based gravitational wave detector, LISA.
The overall goal is for less researcher time to be spent writing code and more time spent doing physics. Currently there exist multiple scattered black hole perturbation theory codes developed by a wide array of individuals or groups over a number of decades. I will describe this project which aims to bring together some of the core elements of these codes into a Toolkit that can be used by all.
Development of the Toolkit, https://bhptoolkit.org, is led by the researchers at University College Dublin, the University of North Carolina at Chapel Hill and the Kavli Institute for Astrophysics and Space Research at the Massachusetts Institute of Technology.
- Nikodem Poplawski (University of New Haven): Noncommutative momentum and torsional regularization — Tuesday, 12:00pm
We derive the quantum commutation relation for the four-momentum in the presence of spacetime torsion. In the Einstein–Cartan theory of gravity, in which the torsion tensor is coupled to the spin of fermions, this relation can be reduced to a commutation relation for the momentum components. We propose that this relation replaces the integration in the momentum space in Feynman diagrams with the summation over the discrete momentum eigenvalues. We derive a prescription for this summation that agrees with convergent integrals. We show that this prescription regularizes ultraviolet-divergent integrals in loop diagrams. We extend this prescription to tensor integrals. We derive a finite, gauge-invariant vacuum polarization tensor and a finite running coupling. Including loops from all charged fermions, we find a finite value for the bare electric charge of an electron. This regularization, originating from the torsion-generated noncommutativity of the momentum, may therefore provide a realistic, physical mechanism for eliminating infinities in quantum field theory and making renormalization finite.
- Dorota Rosinska (University of Warsaw): Differentially rotating neutron stars in GR — Wednesday, 3:00pm
Differential rotation can play an important role in e.g. the dynamical stability of the remnant formed in the coalescence of binary neutron stars. Depending on the degree of differential rotation and the stifness of an equation of state the merger remnant can collapse to a black hole or be temporarily supported by rotation against collapse. I will present a new investigation on the structure of differentially rotating neutron stars, using a well tested, multi-domain relativistic spectral code (Ansorg, Gondek-Rosinska, Villain, 2009). The high level of accuracy and stability of the code enables us for the first time the classification of differentially rotating neutron stars in general relativity. We have found various types of configurations which were not considered in previous works, mainly due to numerical limitations. The maximum allowed mass for the new types of configurations and moderate degree of differential rotation can be even 2-4 times higher then the maximum mass of non-rotating NSs with the same EOS. Obtained results give a new view on properties of differentially rotating neutron stars and are the starting point to study in a systematic way their stability.
- Pradyumn Sahoo (BITS-Pilani): Bouncing scenarios in f(R,T) gravity models — Cancelled
- Jessica Santiago (Victoria University of Wellington): Thermodynamic equilibrium in General Relativity — Tuesday, 11:30am
In this talk we will review Tolman’s relation for temperature gradients in thermal equilibrium states. We will do that by presenting a simplified derivation of this effect, based on the relativistic Euler equation. This will lead naturally to an extension of Tolman-like thermal gradients to the case of stationary spacetimes for fluids with general four-velocities. We will then explore the concept of thermodynamic equilibrium for fluids moving in a curved space-time.
- Volker Schlue (University of Melbourne): On the stability of expanding black hole spacetimes — Thursday, 10:30am
In the context of Einstein's equations with positive cosmological constant, the Kerr de Sitter family of solutions are a model of a black hole in the expanding universe. In this talk, I will describe recent progress on the stability problem for the cosmological region of Schwarzschild de Sitter spacetimes, which can be formulated as a characteristic initial value problem to the future of the cosmological horizons. The dominant stability mechanism is the expansion of the spacetime which leads to decay of the conformal Weyl curvature, but has a surprising destabilizing effect on solutions to the eikonal equation, which play a central role in the formulation of the Cauchy problem in double null gauge.
- Sebastian Schuster (Victoria University of Wellington): Sparsity — Quantifying the Difference Between Hawking Radiation and Black Body Radiation — Wednesday, 3:30pm
In the mid-1970s, Stephen Hawking discovered the evaporation of black holes. Since then it has not just become a hallmark of quantum field theory in curved space-time, but also one of the most important clues towards a quantum theory of gravity. The subsequent decades have seen advances of formal, numerical, and pedagogical nature; yet just as much formation of folklore. Core and center to both folklore and advances is the comparison of black hole radiation to black body radiation. In this talk we shall present a heuristic quantity, "sparsity", for quickly performing this comparison. This quantity is simple to explain, easy to calculate, and helps illustrate the differences and commonalities of the two types of radiation. Beyond this, it is also possible to extend results from the original, 3+1-dimensional contexts to higher dimensions. We reproduce results regarding the different emission characteristics of different particle species in higher dimension known from previous numerical studies in the literature.
- Alex Simpson (Victoria University of Wellington): From black bounce to traversable wormhole — Tuesday, 4:00pm
I will discuss a simple 1-parameter toy model that neatly interpolates between a regular black hole in the form of a "black bounce", the ordinary Schwarzschild solution, and a Morris-Thorne-like traversable wormhole.
- Jiro Soda (Kobe University): Beyond anisotropic inflation — Thursday, 10:30am
In conventional inflation, the universe is expanding isotropically. It is also believed that the anisotropy will be soon washed out. In spite of this conventional belief, I will show that anisotropic inflation is possible. Remarkably, the anisotropic inflation produces the statistical anisotropy in CMB. This can be regarded as the spontaneous symmetry break down of the rotational symmetry. I will also discuss various extensions of the anisotropic inflation.
- Kunihito Uzawa (Kwansei Gakuin University): Slow-roll inflation and the swampland — Thursday, 11:00am
In this talk, we show how the swampland conjecture, which has recently been attracting attention in string theory and gravity theory, relates to the slow-roll condition of inflation. First, we will briefly explain the reason why we focus on the swampland conjecture to investigate the dynamics of inflation. Next, we discuss the behavior of the scalar field describing the evolution of the inflationary scenario from the viewpoint of the swampland conjecture. Finally, we present the implications of energy conditions on cosmological compactification solutions of the higher-dimensional Einstein field equations, and show the relation between the slow-roll condition in the inflationary scenario and the swampland criterion.
- Matt Visser (Victoria University of Wellington): Kiselev black holes — a study in forensic physics — Thursday, 3:00pm
Kiselev black holes are an extremely popular toy model, with well over 200 citations to date. Despite some 200 citations stating the contrary:
- Kiselev black holes are not perfect fluid spacetimes;
- Kiselev black holes have nothing to do with quintessence.
What went wrong? I shall present an exercise in forensic physics; And show that this is an example of group-think… This phenomenon is more common than we would like to think…
- Robert Ward (Australian National University): Precision measurement of space-time: astronomy with gravitational radiation — Thursday, 1:30pm
The age of gravitational wave astronomy has dawned: we now have a new form of radiation with which to study the Universe. On September 14, 2015, the Laser Interferometer Gravitational Wave Observatory (LIGO) detectors recorded the first direct observation by humankind of gravitational waves -- space-time distortions generated by objects with extreme gravity. These waves propagate over astrophysical distances and can be detected by the modulation imposed on the optical path of a suspended mirror laser interferometer. Modern laser interferometric gravitational wave detectors are giant, broadband opto-mechanical sensors that explore the audio spectrum from 1 Hz to 10 kHz. This entire frequency band is expected to contain signals from dynamical astrophysical processes of great interest, such as the inspiral and merger of compact objects, stellar core-collapse supernovae, spinning neutron stars and various astrophysical backgrounds. Even more tantalising are the unpredicted sources. I will discuss gravitational waves and the technology and instrumentation developed to detect them. I will describe what we have observed so far, and the instrumentation-focussed research program at the Australian National University aiming to expand the horizons of gravitational wave detectors by attacking the limiting noise sources, of fundamental and technical origin.
- Karl Wette (Australian National University): Continuous Gravitational Waves from Rapidly Rotating Neutron Stars — Wednesday, 1:30pm
The LIGO and Virgo gravitational-wave detectors have successfully observed numerous short-lived gravitational-wave events from the collision and merger of binary black hole and binary neutron star systems. Long-lived continuous gravitational waves, for which the most likely source is hypothesized to be rapidly-rotating non-axisymmetric neutron stars, have yet to be detected. I will present an overview of past and present efforts to search for continuous gravitational waves, and the data analysis challenges such searches entail.
- Ben Whale (University of Wollongong): Causality and Continuity of the Lorentzian distance — Cancelled
- David Wiltshire (University of Canterbury): Tension in the debate about cosmic expansion — Thursday, 11:30am
The discrepancy in values of the Hubble constant derived on small and large scales using the standard Lambda Cold Dark Matter cosmology is attracting increasing attention. From the point of view of proponents of backreaction of inhomogeneities, scale dependence of estimates of the Hubble constant is to be expected, so this situation is unsurprising. In this talk I will expose cosmic cans of worms relating to systematic uncertainties in the analysis of supernova data, and discuss issues that need to be confronted to perform genuine precision cosmology in future.
Abstracts for Teachers' Outreach Workshop
- Jackie Bondell (OzGrav, Swinburne University of Technology): Gravitational Waves in the Secondary Classroom and Virtual Reality in Physics Education — Friday, 1:30pm
Since the first observation of gravitational waves in 2015, the science of detecting and interpreting gravitational waves events has steadily become more advanced with increasingly precise and frequent observations. This workshop will be delivered in two parts.
In the first session, we will review the latest advancements in gravitational wave science. Then we will introduce teachers to multiple activities that can be used in the classroom to introduce Physics students to some of the major concepts related to understanding and detecting gravitational waves. Teachers will have the opportunity to participate in these activities and will receive materials with curriculum links to incorporate these activities in their own classrooms.
In the second part, we will focus on stellar evolution and answering the questions about where black holes and neutron stars come from. OzGrav educators have developed a program called Mission Gravity which combines scientific modelling with interactive virtual reality (VR). We will collaborate in teams, creating models of stellar evolution via collecting and analysing data from virtual reality trips to stars. Teachers will not only experience the lesson and learn how to adapt it for their schools, but will also learn about designing a science lesson that effectively incorporates VR into student-centred activities while aligning with curriculum standards.
- Shon Shachar Boublil (University of Western Australia and Einstein-First project): Einstein’s Theory of Gravity: Free Fall and Bending Space-Time — Friday, 9:00am
The Einstein-First project aims to change the paradigm of school science teaching through introducing Einsteinian concepts such as space, time, gravity and quanta at an early age. These concepts, rarely taught to schools, have their central importance to modern science, technology and our current understanding of physical nature. One key to implementing an Einsteinian physics curriculum is developing good models and analogies for developing a scientific mind.
This workshop will focus on introducing various activities for classroom settings to introduce Einstein’s Theory of Gravity. This workshop will make use of the spacetime simulator and will investigate the limits and strengths to using this model extensively. We will present a systematic approach based on the use of models through a learning progression designed to create a deep conceptual understanding of general relativity. We will do concept building using qualitative and quantitative experiments. This workshop will be a hand-on experience in learning how to adapt these activity based lessons to the school curriculum.
- Matt Visser (Victoria University of Wellington): _Relativity and Gravitation in High School _ — Friday, 12:00pm
I will discuss some features of relativity and gravitation at high-school level, touching on both special and general relativity, and then discuss some easy but significant things that can be said about tidal forces at high-school level. I will give a mixture of some simple examples and a few warnings.