Cosmology and Gravitation

696 talks

S004

Collection TypeSeries

SubjectAstrophysics

Source RepositoryPIRSA

Displaying 361 - 372 of 696

Numerical investigations of singularities in general relativity

David Garfinkle Oakland University
June 26, 2014

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

John Moffat Perimeter Institute for Theoretical Physics
June 12, 2014

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

Valerio Faraoni Bishop's University
June 10, 2014

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

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

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

Brian Dolan Maynooth University
May 20, 2014

PIRSA:14050093
Astrophysics
Random models of inflation

Andrew Liddle University of Lisbon
May 13, 2014

PIRSA:14050007
Astrophysics
The Case for an Alternative Cosmology

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

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

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

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

Arif Babul University of Victoria
April 15, 2014

PIRSA:14040133
Astrophysics
Is the Milky Way Ringing?

Lawrence Widrow Queen's University
April 08, 2014

PIRSA:14040137
Astrophysics
The not-so-homogeneous universe

Phil Bull Queen Mary University of London
April 01, 2014

PIRSA:14040129
Astrophysics
Cosmic initial conditions and the CMB

Daniel Grin California Institute of Technology
March 25, 2014

PIRSA:14030112
Astrophysics

Numerical investigations of singularities in general relativity

David Garfinkle Oakland University
June 26, 2014

PIRSA:14060052
Astrophysics
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
Astrophysics
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
Astrophysics
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
Astrophysics
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 Maynooth University
May 20, 2014

PIRSA:14050093
Astrophysics
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
Astrophysics
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
Astrophysics
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
Astrophysics
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
Astrophysics
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
Astrophysics
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.
The not-so-homogeneous universe

Phil Bull Queen Mary University of London
April 01, 2014

PIRSA:14040129
Astrophysics
The assumption of spatial homogeneity lies at the heart of the concordance cosmological model. But as I will discuss, truly solid empirical evidence for global (statistical) homogeneity is lacking, and tricky theoretical issues abound. I review a few recent advances in understanding the role inhomogeneity plays in cosmology, including some unexpected effects on light propagation, the death (and rebirth) of backreaction, and impending observational annoyances related to the lumpy local Universe. I'll also talk about some near-future observations that can give us a handle on these effects
Cosmic initial conditions and the CMB

Daniel Grin California Institute of Technology
March 25, 2014

PIRSA:14030112
Astrophysics
One new frontier in cosmology is the frequency spectrum of the CMB. Future instruments may be precise enough to measure deviations from the nearly-perfect blackbody, measuring a chemical potential and thus probing energy injection at extremely high redshift. I will discuss ($\mu$ and $y$-type) CMB spectral distortions from the dissipation of entropy (isocurvature)-sourced acoustic modes. I will then discuss how a high-energy phase transition could also source such distortions. I will then switch gears and talk about the possibility of measuring a spatial fluctuation in the baryon/DM ratio using the CMB, including recent observational results. I may also muse on the surprising possible connection between these compensated isocurvature modes and the anomalously low large-scale scalar power hinted at by Planck observations of the CMB temperature power spectrum and the recent claimed BICEP2 detection of primordial tensor modes

Title	Speaker(s)	Date	Talk Type	Info
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
The not-so-homogeneous universe	Phil Bull	2014-04-01	Scientific Series	View details
Cosmic initial conditions and the CMB	Daniel Grin	2014-03-25	Scientific Series	View details

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Cosmology and Gravitation

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Numerical investigations of singularities in general relativity

Inflation, Variable Speed of Light and BICEP2

Wild and tame scalar-tensor black holes

Some Conceptual Problems in General Relativity and Cosmology

Black holes and Boyle's Law --- the thermodynamics of Einstein's greatest mistake

Random models of inflation

The Case for an Alternative Cosmology

Galileon Maps: Inequivalent Coset Constructions for Spacetime Symmetries

Groups and Clusters of Galaxies: Where Cosmology and Astrophysics Collide

Is the Milky Way Ringing?

The not-so-homogeneous universe

Cosmic initial conditions and the CMB

Numerical investigations of singularities in general relativity

Inflation, Variable Speed of Light and BICEP2

Wild and tame scalar-tensor black holes

Some Conceptual Problems in General Relativity and Cosmology

Black holes and Boyle's Law --- the thermodynamics of Einstein's greatest mistake

Random models of inflation

The Case for an Alternative Cosmology

Galileon Maps: Inequivalent Coset Constructions for Spacetime Symmetries

Groups and Clusters of Galaxies: Where Cosmology and Astrophysics Collide

Is the Milky Way Ringing?

The not-so-homogeneous universe

Cosmic initial conditions and the CMB