Astrophysics

Displaying 1921 - 1932 of 2056

Inflationary Models

William Kinney State University of New York (SUNY)
August 11, 2007

PIRSA:07080017
Astrophysics
Observational Evidence for Dark Matter

Mike Hudson University of Waterloo
August 09, 2007

PIRSA:07080013
Astrophysics
Resolving the Mystery of Dark Matter - EinsteinPlus Keynote Session

James Taylor University of Waterloo
July 20, 2007

PIRSA:07070011
High Energy Physics

Astrophysics
Modified Gravity and its Consequences for the Solar System, Astrophysics and Cosmology

John Moffat Perimeter Institute for Theoretical Physics
May 20, 2007

PIRSA:07050045
Astrophysics
Why there is something rather than nothing

Andrei Barvinski P.N. Lebedev Physical Institute of the Russian Academy of Sciences
May 20, 2007

PIRSA:07050044
Astrophysics
Random Observations in the Landscape

Vitaly Vanchurin University of Minnesota, Duluth
May 20, 2007

PIRSA:07050043
Astrophysics
Dark Energy, Lorentz Violation and Ghosts

Raman Sundrum University of Maryland, College Park
May 20, 2007

PIRSA:07050042
Astrophysics
Consistent Lorentz Violation in Flat and Curved Space

Oriol Pujolas New York University (NYU)
May 20, 2007

PIRSA:07050041
Astrophysics
The DGP Braneworld

Kazuya Koyama University of Portsmouth
May 20, 2007

PIRSA:07050040
Astrophysics
Gravity Probes and Graviton Hair

Georgi Dvali New York University (NYU)
May 20, 2007

PIRSA:07050039
Astrophysics
Why the Vacuum Energy is Enormous (Just Not Here and Now)

Anthony Aguirre University of California, Santa Cruz
May 19, 2007

PIRSA:07050038
Astrophysics
Nonlinear Structure Formation and Apparent Acceleration: An Investigation

Alessio Notari
May 19, 2007

PIRSA:07050037
Astrophysics

Inflationary Models

William Kinney State University of New York (SUNY)
August 11, 2007

PIRSA:07080017
Astrophysics
Observational Evidence for Dark Matter

Mike Hudson University of Waterloo
August 09, 2007

PIRSA:07080013
Astrophysics
Resolving the Mystery of Dark Matter - EinsteinPlus Keynote Session

James Taylor University of Waterloo
July 20, 2007

PIRSA:07070011
High Energy Physics

Astrophysics
For more than 70 years, astronomers have had the uneasy suspicion that there was more to the universe than met the eye - much, much more. In the past five years, this suspicion has become a certainty. We now know for sure that normal matter and normal radiation account for only 4% of the density of the universe. One of the two biggest components, dark matter, may be finally be identified by new experiments coming on line next year. I\'ll summarise the long quest to identify dark matter and our prospects for finally achieving this goal in the next two years.
Modified Gravity and its Consequences for the Solar System, Astrophysics and Cosmology

John Moffat Perimeter Institute for Theoretical Physics
May 20, 2007

PIRSA:07050045
Astrophysics
A relativistic modified gravity (MOG) leads to a self-consistent, stable gravity theory that can describe the solar system, galaxy and clusters of galaxies data and cosmology without dark matter. A review is given of fits to galaxy rotation curves, mass profiles of X-ray clusters and weak and strong lensing of galaxy clusters including the bullet cluster E10657-56. MOG can explain the CMB power spectrum and the observed acceleration of the expansion of the universe.
Why there is something rather than nothing

Andrei Barvinski P.N. Lebedev Physical Institute of the Russian Academy of Sciences
May 20, 2007

PIRSA:07050044
Astrophysics
We show that the recently suggested Euclidean quantum gravity density matrix of the Universe which generates the set of inflationary universes is, in fact, the density matrix of the microcanonical ensemble in {\em Lorentzian} quantum cosmology. This ensemble corresponds to the uniform (weight one) distribution over an entire phase space of {\em true physical variables}, but in terms of the observable spacetime geometry it is peaked about complex saddle-points of the Lorentzian path integral, given by the recently obtained Euclidean gravitational instantons belonging to the bounded range of the cosmological constant. It is shown that the conformal rotation, designed to solve the problem of unboundedness of the Euclidean gravitational action, is, in fact, the manifestation of correct integration range over the lapse and shift functions in Lorentzian quantum gravity, enforcing the Hamiltonian and momentum constraints. Inflationary cosmologies generated by the gravitational instantons at late stages of expansion incorporate cosmological acceleration phenomenon whose low-energy scale can be attained by invoking the ideas of dynamically evolving compactified extra dimensions. Thus, together with the bounded range of the early cosmological constant, this initial state of the Universe simultaneously suggests the dynamical restriction mechanism for the landscape of string vacua and the solution of the dark energy problem.
Random Observations in the Landscape

Vitaly Vanchurin University of Minnesota, Duluth
May 20, 2007

PIRSA:07050043
Astrophysics
Dark Energy, Lorentz Violation and Ghosts

Raman Sundrum University of Maryland, College Park
May 20, 2007

PIRSA:07050042
Astrophysics
I describe how vacuum energy can be controlled by a symmetry principle that necessitates a ghost sector. I argue that the implied instability of Minkowski spacetime is natural and consistent with experience if gravity is fundamentally Lorentz-violating, and describe attempts to construct such exotic dynamics. I briefly discuss the more robust experimental/observational signatures of such a scenario.
Consistent Lorentz Violation in Flat and Curved Space

Oriol Pujolas New York University (NYU)
May 20, 2007

PIRSA:07050041
Astrophysics
Motivated by the severity of the bounds on Lorentz violation in the presence of ordinary gravity, we study frameworks in which Lorentz violation does not affect the spacetime geometry. We show that there are at least two inequivalent classes of spontaneous Lorentz breaking that even in the presence of gravity result in Minkowski space. The first one generically corresponds to the condensation of tensor fields with tachyonic mass, which in turn is related to ghost-condensation. In the second class, realized in the DGP model or in theories of massive gravity, spontaneous Lorentz breaking is induced by the expectation value of sources. The generalization to de-Sitter space is also discussed.
The DGP Braneworld

Kazuya Koyama University of Portsmouth
May 20, 2007

PIRSA:07050040
Astrophysics
In this talk, I summarize a current status of the DGP braneworld emphasizing the theoretical consistency of the model.First I review the behaviour of the linearized gravity and show the existence of the ghost. Then I discuss the issue of the non-linearity of gravity in this model.
Gravity Probes and Graviton Hair

Georgi Dvali New York University (NYU)
May 20, 2007

PIRSA:07050039
Astrophysics
Why the Vacuum Energy is Enormous (Just Not Here and Now)

Anthony Aguirre University of California, Santa Cruz
May 19, 2007

PIRSA:07050038
Astrophysics
Nonlinear Structure Formation and Apparent Acceleration: An Investigation

Alessio Notari
May 19, 2007

PIRSA:07050037
Astrophysics
We present analytically solvable nonlinear models of structure formation in a Universe with only dust, using LTB solutions. We show that the luminosity distance-redshift relation has significant corrections at low redshift (Doppler effect). We discuss different possibilities that could further enhance this effect and mimick Dark Energy. We find negligible integrated effect, suppressed by $(L/R_{H})^3$ (where $L$ is the size of the structure, and $R_{H}$ is the Hubble radius) and we make contact with cosmological perturbation theory.

Title	Speaker(s)	Date	Talk Type	Info link
Inflationary Models	William Kinney	2007-08-11		View details
Observational Evidence for Dark Matter	Mike Hudson	2007-08-09		View details
Resolving the Mystery of Dark Matter - EinsteinPlus Keynote Session	James Taylor	2007-07-20		View details
Modified Gravity and its Consequences for the Solar System, Astrophysics and Cosmology	John Moffat	2007-05-20	Conference	View details
Why there is something rather than nothing	Andrei Barvinski	2007-05-20	Conference	View details
Random Observations in the Landscape	Vitaly Vanchurin	2007-05-20	Conference	View details
Dark Energy, Lorentz Violation and Ghosts	Raman Sundrum	2007-05-20	Conference	View details
Consistent Lorentz Violation in Flat and Curved Space	Oriol Pujolas	2007-05-20	Conference	View details
The DGP Braneworld	Kazuya Koyama	2007-05-20	Conference	View details
Gravity Probes and Graviton Hair	Georgi Dvali	2007-05-20	Conference	View details
Why the Vacuum Energy is Enormous (Just Not Here and Now)	Anthony Aguirre	2007-05-19	Conference	View details
Nonlinear Structure Formation and Apparent Acceleration: An Investigation	Alessio Notari	2007-05-19	Conference	View details

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Format results

Inflationary Models

Observational Evidence for Dark Matter

Resolving the Mystery of Dark Matter - EinsteinPlus Keynote Session

Modified Gravity and its Consequences for the Solar System, Astrophysics and Cosmology

Why there is something rather than nothing

Random Observations in the Landscape

Dark Energy, Lorentz Violation and Ghosts

Consistent Lorentz Violation in Flat and Curved Space

The DGP Braneworld

Gravity Probes and Graviton Hair

Why the Vacuum Energy is Enormous (Just Not Here and Now)

Nonlinear Structure Formation and Apparent Acceleration: An Investigation

Inflationary Models

Observational Evidence for Dark Matter

Resolving the Mystery of Dark Matter - EinsteinPlus Keynote Session

Modified Gravity and its Consequences for the Solar System, Astrophysics and Cosmology

Why there is something rather than nothing

Random Observations in the Landscape

Dark Energy, Lorentz Violation and Ghosts

Consistent Lorentz Violation in Flat and Curved Space

The DGP Braneworld

Gravity Probes and Graviton Hair

Why the Vacuum Energy is Enormous (Just Not Here and Now)

Nonlinear Structure Formation and Apparent Acceleration: An Investigation