Excursions in the Dark Workshop - 2007

Consistent Lorentz Violation in Flat and Curved Space

Oriol Pujolas New York University (NYU)
May 20, 2007
PIRSA:07050041
Cosmology
Dark Energy, Lorentz Violation and Ghosts

Raman Sundrum University of Maryland, College Park
May 20, 2007
PIRSA:07050042
Cosmology
Random Observations in the Landscape

Vitaly Vanchurin University of Minnesota, Duluth
May 20, 2007
PIRSA:07050043
Cosmology
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
Cosmology
Modified Gravity and its Consequences for the Solar System, Astrophysics and Cosmology

John Moffat Perimeter Institute for Theoretical Physics
May 20, 2007
PIRSA:07050045
Cosmology

Consistent Lorentz Violation in Flat and Curved Space

Oriol Pujolas New York University (NYU)
May 20, 2007
PIRSA:07050041
Cosmology
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.
Dark Energy, Lorentz Violation and Ghosts

Raman Sundrum University of Maryland, College Park
May 20, 2007
PIRSA:07050042
Cosmology
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.
Random Observations in the Landscape

Vitaly Vanchurin University of Minnesota, Duluth
May 20, 2007
PIRSA:07050043
Cosmology
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
Cosmology
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.
Modified Gravity and its Consequences for the Solar System, Astrophysics and Cosmology

John Moffat Perimeter Institute for Theoretical Physics
May 20, 2007
PIRSA:07050045
Cosmology
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.

Title	Speaker(s)	Date	Talk Type	Info
Consistent Lorentz Violation in Flat and Curved Space	Oriol Pujolas	2007-05-20	Conference	View details
Dark Energy, Lorentz Violation and Ghosts	Raman Sundrum	2007-05-20	Conference	View details
Random Observations in the Landscape	Vitaly Vanchurin	2007-05-20	Conference	View details
Why there is something rather than nothing	Andrei Barvinski	2007-05-20	Conference	View details
Modified Gravity and its Consequences for the Solar System, Astrophysics and Cosmology	John Moffat	2007-05-20	Conference	View details

Excursions in the Dark Workshop - 2007

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