Astrophysics

Displaying 2041 - 2052 of 2173

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
Non-Anthropic Approaches to the String Landscape

G. Watson University of Michigan–Ann Arbor
May 19, 2007

PIRSA:07050036
Astrophysics
Large Extra Dimensions and Darkness From String Theory

Fernando Quevedo University of Cambridge
May 19, 2007

PIRSA:07050035
Astrophysics
Explorations in Supersymmetric Large Extra Dimensions

Susha Parameswaran University of Liverpool
May 18, 2007

PIRSA:07050033
Astrophysics
Dark Energy and Neutrino Mass

Urbano Franca Harvard University
May 18, 2007

PIRSA:07050032
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
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.
Non-Anthropic Approaches to the String Landscape

G. Watson University of Michigan–Ann Arbor
May 19, 2007

PIRSA:07050036
Astrophysics
We consider the effect that dynamical selection principles could have on the string landscape and for determining the value of the cosmological constant. The underlying symmetries of string theory, along with the dynamics of moduli in the low energy effective field theory, seem to suggest that not all vacua are created equal. However, in some simple models many vacua are alike and this degeneracy may suggest a *non-anthropic* approach to understanding the observed value of the cosmological constant. The approach may also lead to a viable model of inflation, without the need of fine-tuned potentials.
Large Extra Dimensions and Darkness From String Theory

Fernando Quevedo University of Cambridge
May 19, 2007

PIRSA:07050035
Astrophysics
Explorations in Supersymmetric Large Extra Dimensions

Susha Parameswaran University of Liverpool
May 18, 2007

PIRSA:07050033
Astrophysics
Brane worlds may provide insight into the cosmological constant problem because a large vacuum energy on the brane can curve the extra dimensions rather than the local 4D spacetime. Moreover, such models with supersymmetric large extra dimensions reveal a tantalizing numerology, in which the size of the two extra dimensions can lead not only to the electroweak hierarchy but also to the observed dark energy scale. I will review this proposal, its promises and problems, and then describe some of the novel physics that can arise in 6D brane worlds. The dynamical stability of models in 6D supergravity constrains the matter content of the theory, but surprisingly this can be relaxed with negative tension branes. Meanwhile, the Kaluza-Klein mass gap can remain finite even in the infinite volume limit.
Dark Energy and Neutrino Mass

Urbano Franca Harvard University
May 18, 2007

PIRSA:07050032
Astrophysics
One of the possible explanations for the current acceleration of the universe comes from a coupling between the Dark Energy and the Neutrino sectors. This coupling causes the neutrino mass to vary with cosmic time, what opens a new window to constrain this dark energy candidate. In this work, we analyze the mass-varying neutrino scenario in a model independent way, focusing on its effects for the Cosmic Microwave Background and Large Scale Structure.

Title	Speaker(s)	Date	Talk Type	Info link
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
Non-Anthropic Approaches to the String Landscape	G. Watson	2007-05-19	Conference	View details
Large Extra Dimensions and Darkness From String Theory	Fernando Quevedo	2007-05-19	Conference	View details
Explorations in Supersymmetric Large Extra Dimensions	Susha Parameswaran	2007-05-18	Conference	View details
Dark Energy and Neutrino Mass	Urbano Franca	2007-05-18	Conference	View details

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Format results

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

Non-Anthropic Approaches to the String Landscape

Large Extra Dimensions and Darkness From String Theory

Explorations in Supersymmetric Large Extra Dimensions

Dark Energy and Neutrino Mass

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

Non-Anthropic Approaches to the String Landscape

Large Extra Dimensions and Darkness From String Theory

Explorations in Supersymmetric Large Extra Dimensions

Dark Energy and Neutrino Mass