Talks

15721 - 15732 of 16889 Results

RHIC Serves the Perfect Liquid? - Fact or Fiction? Success and Puzzles From 5 Years of RHIC Experiments

Ulrich Heinz Ohio State University

May 22, 2007

PIRSA:07050047

Quantum Fields and Strings
Efficient quantum algorithms for an additive approximation of the Tutte polynomial and the q-state Potts model.

Itai Arad Hebrew University of Jerusalem

May 21, 2007

PIRSA:07050024

Quantum Information
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
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
Random Observations in the Landscape

Vitaly Vanchurin University of Minnesota Duluth

May 20, 2007

PIRSA:07050043

Cosmology
Dark Energy, Lorentz Violation and Ghosts

Raman Sundrum University of Maryland, College Park

May 20, 2007

PIRSA:07050042

Cosmology
Consistent Lorentz Violation in Flat and Curved Space

Oriol Pujolas New York University (NYU)

May 20, 2007

PIRSA:07050041

Cosmology
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

RHIC Serves the Perfect Liquid? - Fact or Fiction? Success and Puzzles From 5 Years of RHIC Experiments

Ulrich Heinz Ohio State University

May 22, 2007

PIRSA:07050047

Quantum Fields and Strings
Efficient quantum algorithms for an additive approximation of the Tutte polynomial and the q-state Potts model.

Itai Arad Hebrew University of Jerusalem

May 21, 2007

PIRSA:07050024

Quantum Information

I will present an efficient quantum algorithm for an additive approximation of the famous Tutte polynomial of any planar graph at any point. The Tutte polynomial captures an extremely wide range of interesting combinatorial properties of graphs, including the partition function of the q-state Potts model. This provides a new class of quantum complete problems. Our methods generalize the recent AJL algorithm for the approximation of the Jones polynomial; instead of using unitary representations, we allow non-unitarity, which seems counter intuitive in the quantum world. Significant contribution of this is a proof that non-unitary operators can be used for universal quantum computation.
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.
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.
Random Observations in the Landscape

Vitaly Vanchurin University of Minnesota Duluth

May 20, 2007

PIRSA:07050043

Cosmology
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.
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.
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.

Title	Date	Collection	Type	Info
RHIC Serves the Perfect Liquid? - Fact or Fiction? Success and Puzzles From 5 Years of RHIC Experiments	2007‑05‑22	Exotic States of Hot and Dense Matter - 2007	Conference	View details
Efficient quantum algorithms for an additive approximation of the Tutte polynomial and the q-state Potts model.	2007‑05‑21	Quantum Information	Scientific Series	View details
Modified Gravity and its Consequences for the Solar System, Astrophysics and Cosmology	2007‑05‑20	Excursions in the Dark Workshop - 2007	Conference	View details
Why there is something rather than nothing	2007‑05‑20	Excursions in the Dark Workshop - 2007	Conference	View details
Random Observations in the Landscape	2007‑05‑20	Excursions in the Dark Workshop - 2007	Conference	View details
Dark Energy, Lorentz Violation and Ghosts	2007‑05‑20	Excursions in the Dark Workshop - 2007	Conference	View details
Consistent Lorentz Violation in Flat and Curved Space	2007‑05‑20	Excursions in the Dark Workshop - 2007	Conference	View details
The DGP Braneworld	2007‑05‑20	Excursions in the Dark Workshop - 2007	Conference	View details
Gravity Probes and Graviton Hair	2007‑05‑20	Excursions in the Dark Workshop - 2007	Conference	View details
Why the Vacuum Energy is Enormous (Just Not Here and Now)	2007‑05‑19	Excursions in the Dark Workshop - 2007	Conference	View details
Nonlinear Structure Formation and Apparent Acceleration: An Investigation	2007‑05‑19	Excursions in the Dark Workshop - 2007	Conference	View details
Non-Anthropic Approaches to the String Landscape	2007‑05‑19	Excursions in the Dark Workshop - 2007	Conference	View details

Format results