Cosmology and Gravitation

Displaying 337 - 348 of 674

Probing the Physics of Active Galaxies Using Multi-wavelength Data

Prajval Shastri
Indian Institute of Astrophysics
August 05, 2014

PIRSA:14080000
Cosmology
Cosmological Coincidence Problem
July 15, 2014

PIRSA:14070030
Cosmology
Numerical investigations of singularities in general relativity

David Garfinkle
Oakland University
June 26, 2014

PIRSA:14060052
Cosmology
Inflation, Variable Speed of Light and BICEP2

John Moffat
Perimeter Institute for Theoretical Physics
June 12, 2014

PIRSA:14060044
Cosmology
Wild and tame scalar-tensor black holes

Valerio Faraoni
Bishop's University
June 10, 2014

PIRSA:14060043
Cosmology
Some Conceptual Problems in General Relativity and Cosmology

Jayant Narlikar
IUCAA - The Inter-University Centre for Astronomy and Astrophysics
June 03, 2014

PIRSA:14060004
Cosmology
Black holes and Boyle's Law --- the thermodynamics of Einstein's greatest mistake

Brian Dolan
National University of Ireland
May 20, 2014

PIRSA:14050093
Cosmology
Random models of inflation

Andrew Liddle
University of Lisbon
May 13, 2014

PIRSA:14050007
Cosmology
The Case for an Alternative Cosmology

Jayant Narlikar
IUCAA - The Inter-University Centre for Astronomy and Astrophysics
May 06, 2014

PIRSA:14050034
Cosmology
Galileon Maps: Inequivalent Coset Constructions for Spacetime Symmetries

Gabirele Trevisan
SISSA International School for Advanced Studies
April 29, 2014

PIRSA:14040132
Cosmology
Groups and Clusters of Galaxies: Where Cosmology and Astrophysics Collide

Arif Babul
University of Victoria
April 15, 2014

PIRSA:14040133
Cosmology
Is the Milky Way Ringing?

Lawrence Widrow
Queen's University
April 08, 2014

PIRSA:14040137
Cosmology

Probing the Physics of Active Galaxies Using Multi-wavelength Data

Prajval Shastri
Indian Institute of Astrophysics
August 05, 2014

PIRSA:14080000
Cosmology
Accreting supermassive black holes in the centres of galaxies (i.e. Active Galactic Nuclei - AGN) are now known to play a prominent role in the growth of galaxies through cosmic time. The fundamental parameters to explain the whole range of observed properties of these accreting systems, however, is still elusive. We will present some results from multi-wavelength investigations of the nature of accreting supermassive black holes, including those that produce low kinetic power jets as well as high kinetic power, relativistic jets.
Cosmological Coincidence Problem
July 15, 2014

PIRSA:14070030
Cosmology
I will try to explain how cosmological coincidence of the two values, the matter energy density and the dark energy density, at the present epoch based on a single scalar field model whith a quartic potential, non-mimimally interacting with gravity. Dark energy in this model originates from the potential energy of the scalar field, which is sourced by the appearance of non-relativistic matter at the time z~ 10^10. No fine tuning of parameter are neccessary.
Numerical investigations of singularities in general relativity

David Garfinkle
Oakland University
June 26, 2014

PIRSA:14060052
Cosmology
The singularity theorems of general relativity tell us that spacetime singularities form in gravitational collapse, but tell us very little about the precise nature of these singularities. More information can be found using analytic approximations and numerical simulations. It is conjectured that inside black holes are two types of singularities: one that is spacelike, local, and oscillatory, and the other that is null and weak. This talk will review what numerical simulations of singularities have been done and the extent to which the above conjecture has been verified by the simulations.
Inflation, Variable Speed of Light and BICEP2

John Moffat
Perimeter Institute for Theoretical Physics
June 12, 2014

PIRSA:14060044
Cosmology
A variable speed of light (VSL) cosmology is developed with a spontaneous breaking of Lorentz invariance in the early universe. A non-minimal electromagnetic coupling to curvature and the resulting quantum electrodynamic vacuum polarization dispersive medium can produce c >> c0 in the early universe, where c0 is the measured speed of light today. Higher derivative curvature contributions to the effective gravitational action and quantum gravity vacuum polarization can produce a dispersive medium and a large increase in the speed of gravitational waves cg >> cg0 in the early universe, where cg0 is the speed of gravitational waves today. The initial value problems of cosmology are solved: the horizon and flatness problems. The model predicts primordial scalar and tensor fluctuation spectral indices ns=0.96 and nt=- 0.04, respectively. The BICEP2 observation of r=0.2 yields r/nt=-5 which is close to the single-field inflationary consistency condition r/nt=-8.
Wild and tame scalar-tensor black holes

Valerio Faraoni
Bishop's University
June 10, 2014

PIRSA:14060043
Cosmology
In scalar-tensor gravity, black holes do not obey the Jebsen-Birkhoff theorem. Non-isolated black holes can be highly dynamical and the teleological concept of event horizon is replaced by the apparent or trapping horizon. Dynamical solutions describing inhomogeneities embedded in cosmological "backgrounds" and the phenomenology of their apparent horizons, which often appear/vanish in pairs, will be described. Isolated black holes, in contrast, have no hair and are the same as in general relativity.
Some Conceptual Problems in General Relativity and Cosmology

Jayant Narlikar
IUCAA - The Inter-University Centre for Astronomy and Astrophysics
June 03, 2014

PIRSA:14060004
Cosmology
This talk will try to highlight some basic problems connected with conclusions uncritically drawn from well known works. These include: 1. The Schwarzschild solution 2. The formation of black holes by gravitational collapse 3. The no hair theorem 4. The principle of equivalence in the very early universe.
Black holes and Boyle's Law --- the thermodynamics of Einstein's greatest mistake

Brian Dolan
National University of Ireland
May 20, 2014

PIRSA:14050093
Cosmology
The thermodynamics of black holes will be reviewed and recent developments incorporating pressure into the first law described. The asymptotically AdS Kerr metric has a van der Waals type critical point with a line of first order phase transitions terminating at a critical point with mean field exponents. The phase structure and stability of black holes in higher dimensions will also be described.
Random models of inflation

Andrew Liddle
University of Lisbon
May 13, 2014

PIRSA:14050007
Cosmology
Rather than writing down specific functional forms, one can generate inflation models via stochastic processes in order to explore generic properties of inflation models. I describe our explorations of the phenomenology of randomly-generated multi-field inflation models, both for canonical fields and for a braneworld-motivated scenario. Implications of some recent observational results, including BICEP2, will be discussed.
The Case for an Alternative Cosmology

Jayant Narlikar
IUCAA - The Inter-University Centre for Astronomy and Astrophysics
May 06, 2014

PIRSA:14050034
Cosmology
This talk will describe the Quasi-Steady State Cosmology proposed in 1993 by Fred Hoyle, Geoffrey Burbidge and Jayant Narlikar. Starting with the motivation for this exercise, a formal field theoretic framework inspired by Mach’s principle is shown to lead to this model. The model is a generalization of the classical steady state model in the sense that it is driven by a scalar field which causes creation in explosive form. Such ‘minicreation events’ lead to a universe with a long term de Sitter expansion superposed with oscillations of shorter time scales. It is shown that this cosmology explains all the observed cosmological features and that there exist potential tests to distinguish between this cosmology and the standard big bang cosmology.
Galileon Maps: Inequivalent Coset Constructions for Spacetime Symmetries

Gabirele Trevisan
SISSA International School for Advanced Studies
April 29, 2014

PIRSA:14040132
Cosmology
Non-linear realizations of spacetime symmetries can be obtained by a generalization of the coset construction valid for internal ones. The physical equivalence of different representations for spacetime symmetries is not obvious, since their relation involves not only a redefinition of the fields but also a field-dependent change of coordinates. A simple and relevant spacetime symmetry is obtained by the contraction of the 4D conformal group that leads to the Galileon group. In this talk I will analyze two non-linear realizations of this group, focusing in particular on the propagation of signals around non-trivial backgrounds.
Groups and Clusters of Galaxies: Where Cosmology and Astrophysics Collide

Arif Babul
University of Victoria
April 15, 2014

PIRSA:14040133
Cosmology
Groups and clusters of galaxies are the most massive gravitationally bound objects in the Universe. They are also the most recent cosmic objects to form. In the currently accepted models of cosmic structure formation, the number density distribution of the most massive of these systems, and how this has been changing with time, depend sensitively to the parameters describing the large-scale geometry and the expansion history of the universe. However, to exploit galaxy clusters as cosmological probes, we must be able to relate their observable properties to their total mass. I will discuss our ongoing effort to calibrate the X-ray/SZ observations to the total mass for the 50 clusters comprising the Canadian Cluster Comparison Project (CCCP) sample. Resulting scaling relations, the associated scatter, and even how these change with time, invariably depend on "astrophysics" unfolding in these systems. The precision with which the cosmological parameters can be determined depends critically on how well we understand why groups and clusters manifest the observed properties that they do. This, however, has proven challenging. I will provide an update of the current state of affairs and highlight some of the key gaps in our understanding of the underlying physics.
Is the Milky Way Ringing?

Lawrence Widrow
Queen's University
April 08, 2014

PIRSA:14040137
Cosmology
Recent observations from three different astronomical surveys have revealed evidence for asymmetries about the Galactic midplane in the kinematics of solar neighborhood stars. These asymmetries appear, in part, as compression-rarefaction modes in the bulk motions of stars perpendicular to the midplane. I will discuss the hypothesis that these motions were caused by the recent passage of a satellite galaxy or dark matter subhalo through the Galactic disk. In short, we may be witnessing the early stages of a disk-heating event during which the Galaxy's disk relaxes to a new state after interacting with substructure from its own halo.

Title	Speaker(s)	Date	Talk Type	Info
Probing the Physics of Active Galaxies Using Multi-wavelength Data	Prajval Shastri	2014-08-05	Scientific Series	View details
Cosmological Coincidence Problem		2014-07-15	Scientific Series	View details
Numerical investigations of singularities in general relativity	David Garfinkle	2014-06-26	Scientific Series	View details
Inflation, Variable Speed of Light and BICEP2	John Moffat	2014-06-12	Scientific Series	View details
Wild and tame scalar-tensor black holes	Valerio Faraoni	2014-06-10	Scientific Series	View details
Some Conceptual Problems in General Relativity and Cosmology	Jayant Narlikar	2014-06-03	Scientific Series	View details
Black holes and Boyle's Law --- the thermodynamics of Einstein's greatest mistake	Brian Dolan	2014-05-20	Scientific Series	View details
Random models of inflation	Andrew Liddle	2014-05-13	Scientific Series	View details
The Case for an Alternative Cosmology	Jayant Narlikar	2014-05-06	Scientific Series	View details
Galileon Maps: Inequivalent Coset Constructions for Spacetime Symmetries	Gabirele Trevisan	2014-04-29	Scientific Series	View details
Groups and Clusters of Galaxies: Where Cosmology and Astrophysics Collide	Arif Babul	2014-04-15	Scientific Series	View details
Is the Milky Way Ringing?	Lawrence Widrow	2014-04-08	Scientific Series	View details

Cosmology and Gravitation

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