Astrophysics

Displaying 1189 - 1200 of 2277

Cosmic flows: testing gravity and the matter power spectrum on very large scales

Mike Hudson University of Waterloo
September 16, 2014

PIRSA:14090077
Astrophysics
Black hole evaporation without firewalls

James Bardeen
September 02, 2014

PIRSA:14090001
Astrophysics
CMB anomalies from primordial gravitational waves

Yi Wang Hong Kong University of Science and Technology
August 13, 2014

PIRSA:14080019
Astrophysics
Algebraic Geometry in Cosmology

Matilde Marcolli University of Toronto
August 07, 2014

PIRSA:14080002
Astrophysics
Probing the Physics of Active Galaxies Using Multi-wavelength Data

Prajval Shastri Indian Institute of Astrophysics
August 05, 2014

PIRSA:14080000
Astrophysics
Cosmological Coincidence Problem
July 15, 2014

PIRSA:14070030
Astrophysics
Numerical investigations of singularities in general relativity

David Garfinkle Oakland University
June 26, 2014

PIRSA:14060052
Astrophysics
On Quantum Tunnelling

Neil Turok University of Edinburgh
June 25, 2014

PIRSA:14060051
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
Neutrino Wakes

Ue-Li Pen University of Toronto
June 06, 2014

PIRSA:14060041
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

Cosmic flows: testing gravity and the matter power spectrum on very large scales

Mike Hudson University of Waterloo
September 16, 2014

PIRSA:14090077
Astrophysics
Peculiar velocities - deviations from Hubble expansion - are the only practical probe of the growth of matter density fluctuations on very large scales in the nearby Universe. I will discuss recent measurements of quantities of cosmological interest from our group and others. One is the "bulk" flow of nearby galaxies with respect to the frame defined by the Cosmic Microwave Background, and what this tells us about fluctuations on large very spatial scales. The second is the measurement of the growth rate of fluctuations, a critical test of Lambda CDM and modified gravity models.
Black hole evaporation without firewalls

James Bardeen
September 02, 2014

PIRSA:14090001
Astrophysics
There need not be any conflict between unitarity, locality, and regularity of the horizon in black hole evaporation. I discuss a scenario in which the initial collapse that forms the black hole results in a small non-singular core inside an inner event horizon. This core grows as the result of quantum back-reaction associated with the increasing entanglement entropy of Hawking radiation quanta and their partners trapped inside the core. By the Page time the inner and outer apparent horizons either merge into a degenerate horizon, shutting off the Hawking radiation and leaving a massive remnant, or they disappear completely, allowing the trapped quantum information to escape. The scenario is justified by appeals to the Bousso covariant entropy bound and the ER=EPR conjecture. The talk is largely based on arxiv.org/1406.4098.
CMB anomalies from primordial gravitational waves

Yi Wang Hong Kong University of Science and Technology
August 13, 2014

PIRSA:14080019
Astrophysics
We relate CMB anomalies and the recent observational evidence of primordial gravitational
waves. Two aspects are investigated:

(a) Several anomalies are spotted on the low ell temperature map of the WMAP and Planck
experiments. However, those anomalies disappear at high ell. We propose that those low ell
temperature anomalies may come from nearly scale invariant anomalies of the tensor sector.
Those anomalies on the temperature map naturally decay towards small scales, characterized
by the tensor-to-temperature radiation transfer function.

(b) The anomalies introduced by the gravitational waves discovery. Strong tension is noticed
between the BICEP2 and Planck data. We study in detail how blue tilt of the tensor spectrum
reconciles the tension between those datasets.
Algebraic Geometry in Cosmology

Matilde Marcolli University of Toronto
August 07, 2014

PIRSA:14080002
Astrophysics
The talk is based on joint work with Yuri Manin (arXiv:1402.2158). Using algebro-geometric blowups it is possible to construct a family of models of gluing of aeons across a Big-Bang type singularity, which includes the case of Penrose's conformally cyclic cosmology, as well as inflationary multiverse models generalizing the "eternal symmetree", and BKLL mixmaster type cosmologies. Using the mixmaster dynamics, formulated in terms of elliptic curves and modular curves, we speculate on the geometry of cosmological time near the gluing of aeons. We show also that this type of model allows for phenomena of noncommutativity of spacetime coordinates near the Big-Bang and the crossing of aeons.
Probing the Physics of Active Galaxies Using Multi-wavelength Data

Prajval Shastri Indian Institute of Astrophysics
August 05, 2014

PIRSA:14080000
Astrophysics
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
Astrophysics
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
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.
On Quantum Tunnelling

Neil Turok University of Edinburgh
June 25, 2014

PIRSA:14060051
Astrophysics
One of the most basic but intriguing properties of quantum systems is their ability to `tunnel' between configurations which are classically disconnected. That is, processes which are classically impossible, are quantum allowed. In this talk I will outline a new, first-principles approach combining the semiclassical approximation with the concepts of post-selection and weak measurement. Its main virtue is to provide a real-time description within which sharp answers can be given to questions such as 'how long did the tunneling take' and 'where was the particle while it was tunneling?' Potential applications span a vast range, from laboratory tests to understanding black hole evaporation, the stability of the electroweak Higgs vacuum and the future of our universe, and the validity (or otherwise) of the "inflationary multiverse" scenario.
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.
Neutrino Wakes

Ue-Li Pen University of Toronto
June 06, 2014

PIRSA:14060041
Astrophysics
We identify a new non-linear neutrino wake effect, due to the streaming motions of neutrinos relative to dark matter, analogous to the Tseliakhovich-Hirata effect. We compute the effect in moving background perturbation theory, compare to direct n-body simulations, and forecast its observability in current and future surveys. Depending on neutrino mass, this effect could be observable in upcoming surveys through a cross correlation dipole in lensing and galaxies. Unlike previous cosmological neutrino effects, this depends primarily on neutrino mass, making it complementary to measurements that depend on neutrino density.
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.

Title	Speaker(s)	Date	Talk Type	Info link
Cosmic flows: testing gravity and the matter power spectrum on very large scales	Mike Hudson	2014-09-16	Scientific Series	View details
Black hole evaporation without firewalls	James Bardeen	2014-09-02	Scientific Series	View details
CMB anomalies from primordial gravitational waves	Yi Wang	2014-08-13	Scientific Series	View details
Algebraic Geometry in Cosmology	Matilde Marcolli	2014-08-07	Scientific Series	View details
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
On Quantum Tunnelling	Neil Turok	2014-06-25	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
Neutrino Wakes	Ue-Li Pen	2014-06-06	Scientific Series	View details
Some Conceptual Problems in General Relativity and Cosmology	Jayant Narlikar	2014-06-03	Scientific Series	View details

Supported by

Format results

Cosmic flows: testing gravity and the matter power spectrum on very large scales

Black hole evaporation without firewalls

CMB anomalies from primordial gravitational waves

Algebraic Geometry in Cosmology

Probing the Physics of Active Galaxies Using Multi-wavelength Data

Cosmological Coincidence Problem

Numerical investigations of singularities in general relativity

On Quantum Tunnelling

Inflation, Variable Speed of Light and BICEP2

Wild and tame scalar-tensor black holes

Neutrino Wakes

Some Conceptual Problems in General Relativity and Cosmology

Cosmic flows: testing gravity and the matter power spectrum on very large scales

Black hole evaporation without firewalls

CMB anomalies from primordial gravitational waves

Algebraic Geometry in Cosmology

Probing the Physics of Active Galaxies Using Multi-wavelength Data

Cosmological Coincidence Problem

Numerical investigations of singularities in general relativity

On Quantum Tunnelling

Inflation, Variable Speed of Light and BICEP2

Wild and tame scalar-tensor black holes

Neutrino Wakes

Some Conceptual Problems in General Relativity and Cosmology