Astrophysics

Displaying 1201 - 1212 of 2162

The cosmological constant and the emergence of the continuum

Lorenzo Sindoni Max Planck Institute for Gravitational Physics - Albert Einstein Institute (AEI)
October 22, 2012

PIRSA:12100081
Astrophysics
An analogue model lesson for the cosmological constant

Stefano Liberati SISSA International School for Advanced Studies
October 22, 2012

PIRSA:12100080
Astrophysics
Maximum entropy, the universal dark matter density profile... and its destruction

Andrew Pontzen University of Oxford
October 16, 2012

PIRSA:12100003
Astrophysics
Voids in the SDSS: from demography to cosmology

Paul Sutter Institut d'Astrophysique de Paris
October 09, 2012

PIRSA:12100041
Astrophysics
Scalars with Higher Derivatives in Supergravity and Cosmology

Jean-Luc Lehners Self Employed
October 09, 2012

PIRSA:12100042
Astrophysics
Massey Lecture - Other location

Neil Turok University of Edinburgh
October 03, 2012

PIRSA:12100133
Astrophysics
Homogeneous and Isotropic Universe from Nonlinear Massive Gravity

A. Emir Gumrukcuoglu
October 02, 2012

PIRSA:12100002
Astrophysics
Supermassive black holes in non-spherical galactic nuclei and enhanced rates of star capture events

Eugene Vasiliev Rochester Institute of Technology
September 25, 2012

PIRSA:12090064
Astrophysics
New developments in massive gravity
September 18, 2012

PIRSA:12090061
Astrophysics

General Relativity & Quantum Cosmology
Spectral distortions of the CMB and what we might learn about early universe physics

Jens Chluba University of Manchester
September 11, 2012

PIRSA:12090060
Astrophysics
Inflation from Magnetic Drift

Mark Wyman PDT Partners LLC
September 04, 2012

PIRSA:12090050
Astrophysics
Dark matter densities on small scales and implications for dark matter models

Manoj Kaplinghat University of California, Irvine
July 24, 2012

PIRSA:12070000
Astrophysics

The cosmological constant and the emergence of the continuum

Lorenzo Sindoni Max Planck Institute for Gravitational Physics - Albert Einstein Institute (AEI)
October 22, 2012

PIRSA:12100081
Astrophysics
Naturalness problems that could be signaling the necessity a completion of an effective field theory with the introduction of an otherwise overlooked ingredient. The cosmological constant problem can be seen as a signal that the EFT for gravity, general relativity, is not correctly including the gravitational properties of the vacuum. Starting from the discussion of the a possible solution to this naturalness problem for a cc-like term in a BEC analogue model, I will briefly discuss how this particular mechanism can be extended, albeit in a preliminary form, to more genuine quantum gravity models like GFT, connecting in particular the problem of the determination of the gravitational couplings (and hence the hierarchies involved) to the appearance of a semiclassical space-time
An analogue model lesson for the cosmological constant

Stefano Liberati SISSA International School for Advanced Studies
October 22, 2012

PIRSA:12100080
Astrophysics
Analogue models of gravity have been a test field for many phenomena in quantum field theory on curved spacetimes. It was recently recognized that in some situations they can also provide toy models of emergent gravity. We shall review here such a model and address within it the nature and scale of the cosmological constrant trying to draw general lessons for emergent gravity scenarios.
Maximum entropy, the universal dark matter density profile... and its destruction

Andrew Pontzen University of Oxford
October 16, 2012

PIRSA:12100003
Astrophysics
I review some recent developments in attempting to reconcile the observed galaxy population with numerical models of structure formation in the 'LCDM' concordance cosmology. Focussing on behaviour of dwarf galaxies, I describe the infamous 'cusp-core' dichotomy -- a long-standing challenge to the LCDM picture on small scales -- and use toy models to show how it is resolved in recent numerical simulations (Pontzen & Governato 2012). I then discuss the current observational status of this picture (Teyssier, Pontzen & Read 2012; Penarrubia et al 2012).

In the second half of the talk, I apply the analytic techniques developed for probing the effect of gas on dark matter dynamics to the question of how, in the absence of baryons, a universal "NFW" dark matter halo profile emerges (independent of scale or details of the initial conditions).

Thus the generation of NFW halos on the one hand and the destruction of their central cusps on the other can be ascribed to surprisingly similar physical arguments.
Voids in the SDSS: from demography to cosmology

Paul Sutter Institut d'Astrophysique de Paris
October 09, 2012

PIRSA:12100041
Astrophysics
Cosmic voids are potentially a rich source of information for both astrophysics and cosmology. To enable such science, we produce the most comprehensive void catalog to date using the Sloan Digital Sky Survey Data Release 7 main sample out to redshift z = 0.2 and the Luminous Red Galaxy sample out to z = 0.44. Using a modified version of the parameter-free void finder ZOBOV, we fully take into account the presence of survey boundary and masks. We discuss basic catalog statistics such as number counts and redshift distributions, as well as describe some example data products derived from our catalog, such as radial density profiles and projected density maps. Using this catalog, we report on the first application of the Alcock-Paczynski test to stacked voids in spectroscopic redshift surveys by applying the shape-fitting procedure presented in Lavaux & Wandelt (2011) to ten void stacks out to redshift z = 0.36. Our results are consistent with WMAP 7-year cosmological constraints. We compare our results to alternate methods of constructing void stacks and comment on future observational prospects.
Scalars with Higher Derivatives in Supergravity and Cosmology

Jean-Luc Lehners Self Employed
October 09, 2012

PIRSA:12100042
Astrophysics
There are many situations in cosmology that motivate the study of scalar fields with higher-derivative actions. The best-known such situations are probably k-inflation (with DBI-inflation being a special case) and models based on galileon theories, but even eternal inflation and cyclic universes provide good reasons to study such theories. After an extended discussion of the motivations, I will show how scalar field theories with higher derivatives can be constructed in (minimal, 4-dimensional) supergravity, and will discuss their properties, especially in regard to their cosmological applications.
Massey Lecture - Other location

Neil Turok University of Edinburgh
October 03, 2012

PIRSA:12100133
Astrophysics
Homogeneous and Isotropic Universe from Nonlinear Massive Gravity

A. Emir Gumrukcuoglu
October 02, 2012

PIRSA:12100002
Astrophysics
The question of finite range gravity, or equivalently, whether graviton can have a non-zero mass, has been one of the major challenges in classical field theory for the last 70 years. Generically, a massive gravity theory contains an extra degree in addition to the 5 polarizations of massive graviton, which turns out to be a ghost. Recently, de Rham, Gabadadze and Tolley constructed a nonlinear theory of massive gravity, which successfully eliminates the ghost. Moreover, the theory has also phenomenological relevance, since the graviton mass may account for the accelerated expansion of the present universe, providing an alternative to dark energy. I will present self-accelerating cosmological solutions in the framework of this theory. The cosmological perturbations around these backgrounds have an interesting behavior: instead of the 5 degrees of freedom expected from a massive spin-2 field, only the 2 gravity wave polarizations are dynamical, at linear level. However, nonlinear analysis of the extra modes reveal the existence of ghost instabilities. This implies that a consistent universe solution in this theory should be inhomogeneous and/or anisotropic.
Supermassive black holes in non-spherical galactic nuclei and enhanced rates of star capture events

Eugene Vasiliev Rochester Institute of Technology
September 25, 2012

PIRSA:12090064
Astrophysics
We consider the stellar-dynamical processes which lead to the capture or tidal disruption of stars by a supermassive black hole, review the standard theory of two-body relaxation and loss-cone repopulation in spherical galactic nuclei, and extend it to the axisymmetric and triaxial nuclear star clusters. In the absense of symmetry which conserves angular momentum, the orbits of stars experience regular or chaotic changes of angular momentum even in the smooth potential of star cluster, which creates a substantial population of "centrophilic" orbits. We discuss the loss cone draining rates, i.e. rates of capture of stars from these orbits. Next we consider the relaxation phenomena in non-spherical nuclei, focusing on the differences between spherical, axisymmetric and triaxial cases. It turns out that the rates of repopulation of the loss cone are moderately higher in non-spherical systems, but in the triaxial case an additional, often substantial, increase of capture rates comes from draining of the centrophilic orbit population.
New developments in massive gravity
September 18, 2012

PIRSA:12090061
Astrophysics

General Relativity & Quantum Cosmology
The idea that the graviton may be massive has seen a resurgence of interest due to recent progress which has overcome its traditional problems. I will review this recent progress, which has led to a consistent ghost-free effective field theory of a massive graviton, with a stable hierarchy between the graviton mass and the cutoff, and how this theory has the potential to resolve the naturalness problem of the cosmological constant.
Spectral distortions of the CMB and what we might learn about early universe physics

Jens Chluba University of Manchester
September 11, 2012

PIRSA:12090060
Astrophysics
The spectrum of the cosmic microwave background (CMB) is known to be extremely close to a perfect blackbody. However, even within standard cosmology several processes occurring in the early Universe lead to distortions of the CMB at a level that might become observable in the future. This could open an exciting new window to early Universe physics. In my talk I will then explain in more detail why the cooling of matter in the early Universe causes a negative mu- and y-type distortion and how the damping of primordial small-scale perturbations before recombination could allow placing interesting constraints on different inflationary models.
Inflation from Magnetic Drift

Mark Wyman PDT Partners LLC
September 04, 2012

PIRSA:12090050
Astrophysics
I will describe a new, generic mechanism for realizing a period of slowly-rolling inflation through the use of an analog of 'magnetic drift.' I will demonstrate how the mechanism works through two particular worked examples: Chromo-Natural Inflation, which exists as a purely 4D effective theory, and a version that can appear naturally in string theory.
Dark matter densities on small scales and implications for dark matter models

Manoj Kaplinghat University of California, Irvine
July 24, 2012

PIRSA:12070000
Astrophysics
We will discuss the estimated densities of dark matter in the central regions of galaxies and discuss their inconsistency with the predictions of cold dark matter only simulations. We will focus on the satellites of the Milky Way to highlight this issue and then explore dark matter with significant self-interactions as a viable alternative. Milky Way satellites also place stringent constraints on WIMP dark matter models in a completely different way through Fermi-LAT observations and we will summarize those results.

Title	Speaker(s)	Date	Talk Type	Info link
The cosmological constant and the emergence of the continuum	Lorenzo Sindoni	2012-10-22	Conference	View details
An analogue model lesson for the cosmological constant	Stefano Liberati	2012-10-22	Conference	View details
Maximum entropy, the universal dark matter density profile... and its destruction	Andrew Pontzen	2012-10-16	Scientific Series	View details
Voids in the SDSS: from demography to cosmology	Paul Sutter	2012-10-09	Scientific Series	View details
Scalars with Higher Derivatives in Supergravity and Cosmology	Jean-Luc Lehners	2012-10-09	Scientific Series	View details
Massey Lecture - Other location	Neil Turok	2012-10-03	Public Lectures	View details
Homogeneous and Isotropic Universe from Nonlinear Massive Gravity	A. Emir Gumrukcuoglu	2012-10-02	Scientific Series	View details
Supermassive black holes in non-spherical galactic nuclei and enhanced rates of star capture events	Eugene Vasiliev	2012-09-25	Scientific Series	View details
New developments in massive gravity		2012-09-18	Scientific Series	View details
Spectral distortions of the CMB and what we might learn about early universe physics	Jens Chluba	2012-09-11	Scientific Series	View details
Inflation from Magnetic Drift	Mark Wyman	2012-09-04	Scientific Series	View details
Dark matter densities on small scales and implications for dark matter models	Manoj Kaplinghat	2012-07-24	Scientific Series	View details

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The cosmological constant and the emergence of the continuum

An analogue model lesson for the cosmological constant

Maximum entropy, the universal dark matter density profile... and its destruction

Voids in the SDSS: from demography to cosmology

Scalars with Higher Derivatives in Supergravity and Cosmology

Massey Lecture - Other location

Homogeneous and Isotropic Universe from Nonlinear Massive Gravity

Supermassive black holes in non-spherical galactic nuclei and enhanced rates of star capture events

New developments in massive gravity

Spectral distortions of the CMB and what we might learn about early universe physics

Inflation from Magnetic Drift

Dark matter densities on small scales and implications for dark matter models

The cosmological constant and the emergence of the continuum

An analogue model lesson for the cosmological constant

Maximum entropy, the universal dark matter density profile... and its destruction

Voids in the SDSS: from demography to cosmology

Scalars with Higher Derivatives in Supergravity and Cosmology

Massey Lecture - Other location

Homogeneous and Isotropic Universe from Nonlinear Massive Gravity

Supermassive black holes in non-spherical galactic nuclei and enhanced rates of star capture events

New developments in massive gravity

Spectral distortions of the CMB and what we might learn about early universe physics

Inflation from Magnetic Drift

Dark matter densities on small scales and implications for dark matter models