Talks

14749 - 14760 of 15910 Results

The DGP Braneworld

Kazuya Koyama University of Portsmouth

May 20, 2007
PIRSA:07050040

Cosmology
Gravity Probes and Graviton Hair

Georgi Dvali New York University (NYU)

May 20, 2007
PIRSA:07050039

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

Anthony Aguirre University of California, Santa Cruz

May 19, 2007
PIRSA:07050038

Cosmology
Nonlinear Structure Formation and Apparent Acceleration: An Investigation

Alessio Notari

May 19, 2007
PIRSA:07050037

Cosmology
Non-Anthropic Approaches to the String Landscape

G. Watson University of Michigan–Ann Arbor

May 19, 2007
PIRSA:07050036

Cosmology
Large Extra Dimensions and Darkness From String Theory

Fernando Quevedo University of Cambridge

May 19, 2007
PIRSA:07050035

Cosmology
Explorations in Supersymmetric Large Extra Dimensions

Susha Parameswaran University of Liverpool

May 18, 2007
PIRSA:07050033

Cosmology
Dark Energy and Neutrino Mass

Urbano Franca Harvard University

May 18, 2007
PIRSA:07050032

Cosmology
Two Topics on the Accelerating Universe

Gregory Gabadadze New York University (NYU)

May 18, 2007
PIRSA:07050030

Cosmology
Dynamics of Linear Perturbations in Modified Gravity Theories

Alessandra Silvestri Leiden University

May 18, 2007
PIRSA:07050031

Cosmology
Embedding Quintessence in Spontaneously Broken N=1 Supergravity

Philippe Brax CEA Saclay

May 18, 2007
PIRSA:07050029

Cosmology
Dark Energy from variation of the fundamental scale

Christof Wetterich Universität Heidelberg

May 18, 2007
PIRSA:07050028

Cosmology

The DGP Braneworld

Kazuya Koyama University of Portsmouth

May 20, 2007
PIRSA:07050040

Cosmology

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

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

Anthony Aguirre University of California, Santa Cruz

May 19, 2007
PIRSA:07050038

Cosmology
Nonlinear Structure Formation and Apparent Acceleration: An Investigation

Alessio Notari

May 19, 2007
PIRSA:07050037

Cosmology

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

Cosmology

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

Cosmology
Explorations in Supersymmetric Large Extra Dimensions

Susha Parameswaran University of Liverpool

May 18, 2007
PIRSA:07050033

Cosmology

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

Cosmology

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.
Two Topics on the Accelerating Universe

Gregory Gabadadze New York University (NYU)

May 18, 2007
PIRSA:07050030

Cosmology
Dynamics of Linear Perturbations in Modified Gravity Theories

Alessandra Silvestri Leiden University

May 18, 2007
PIRSA:07050031

Cosmology

A modification of Gravity in the low-curvature regime may account for the late time acceleration of our universe, and is therefore an interesting alternative to Dark Energy.In such models, the modified Einstein equations admit self-accelerated solutions in the presence of negligible matter. At the level of perturbation theory,the modified equations give rise to new dynamics for the perturbations of the metric and matter. I will consider scalar perturbations, presenting in some details the dynamics of linear perturbations for two specific models, f(R) Gravity and Modified Source Gravity. I will conclude by demonstrating how some characteristic features of these models are likely to be common to general models of Modified Gravity and how Large Scale Structure formation and the Integrated Sachs Wolfe effect might be useful probes to distinguish between Dark Energy and Modified Gravity.
Embedding Quintessence in Spontaneously Broken N=1 Supergravity

Philippe Brax CEA Saclay

May 18, 2007
PIRSA:07050029

Cosmology

I will present the embedding of runaway quintessence models in supergravity coupled to observable matter and hidden supersymmetry breaking. Serious obstructions appear either in the gravitational sector of the theory or cosmologically. Alternatives will be discussed.
Dark Energy from variation of the fundamental scale

Christof Wetterich Universität Heidelberg

May 18, 2007
PIRSA:07050028

Cosmology

We explore the hypothesis that a dynamical dark energy is related to a time-variation of the fundamental mass scale. A dilatation anomaly induced by quantum fluctuations could explain the small value of the present dark energy. Reformulated as a scalar field theory this would predict a quintessence potential which asymptotically relaxes to zero rather than to a nonvanishing constant. An observable consequence of such a scenario results in "early dark energy " contributing a few percent to the energy density of the Universe even at high redshift. Quintessence would be related to a new "fundamental" macroscopic force and induce a small time variation of fundamental constants.

Title	Speaker(s)	Date	Collection	Type	Info
The DGP Braneworld	Kazuya Koyama	2007‑05‑20	Excursions in the Dark Workshop - 2007	Conference	View details
Gravity Probes and Graviton Hair	Georgi Dvali	2007‑05‑20	Excursions in the Dark Workshop - 2007	Conference	View details
Why the Vacuum Energy is Enormous (Just Not Here and Now)	Anthony Aguirre	2007‑05‑19	Excursions in the Dark Workshop - 2007	Conference	View details
Nonlinear Structure Formation and Apparent Acceleration: An Investigation	Alessio Notari	2007‑05‑19	Excursions in the Dark Workshop - 2007	Conference	View details
Non-Anthropic Approaches to the String Landscape	G. Watson	2007‑05‑19	Excursions in the Dark Workshop - 2007	Conference	View details
Large Extra Dimensions and Darkness From String Theory	Fernando Quevedo	2007‑05‑19	Excursions in the Dark Workshop - 2007	Conference	View details
Explorations in Supersymmetric Large Extra Dimensions	Susha Parameswaran	2007‑05‑18	Excursions in the Dark Workshop - 2007	Conference	View details
Dark Energy and Neutrino Mass	Urbano Franca	2007‑05‑18	Excursions in the Dark Workshop - 2007	Conference	View details
Two Topics on the Accelerating Universe	Gregory Gabadadze	2007‑05‑18	Excursions in the Dark Workshop - 2007	Conference	View details
Dynamics of Linear Perturbations in Modified Gravity Theories	Alessandra Silvestri	2007‑05‑18	Excursions in the Dark Workshop - 2007	Conference	View details
Embedding Quintessence in Spontaneously Broken N=1 Supergravity	Philippe Brax	2007‑05‑18	Excursions in the Dark Workshop - 2007	Conference	View details
Dark Energy from variation of the fundamental scale	Christof Wetterich	2007‑05‑18	Excursions in the Dark Workshop - 2007	Conference	View details

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