Cosmology and Gravitation

665 talks

S004

Collection TypeSeries

SubjectAstrophysics

Source RepositoryPIRSA

Displaying 397 - 408 of 665

Recent progress on de Sitter S-matrix

Ian Morrison West Chester University
November 13, 2012

PIRSA:12110043
Astrophysics
Primordial Magnetic Fields & Non-Gaussianity

Martin Sloth University of Southern Denmark
November 06, 2012

PIRSA:12110040
Astrophysics
Kicking Chameleons: Early Universe Challenges for Chameleon Gravity

Adrienne Erickcek University of North Carolina at Chapel Hill
October 25, 2012

PIRSA:12100125
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 Koehn AI
October 09, 2012

PIRSA:12100042
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
Exoplanet observation by microlensing and wave optics features

Sohrab Rahvar Sharif University of Technology

August 14, 2012

PIRSA:12080006

Recent progress on de Sitter S-matrix

Ian Morrison West Chester University
November 13, 2012

PIRSA:12110043
Astrophysics
The de Sitter S-matrix provides a gauge-invariant and field redefinition-invariant window into de Sitter QFTs and may provide a crucial entry in any dS/CFT dictionary. In this talk I will summarize recent progress on developing the S-matrix for theories with gauge fields and perturbative gravity. Nonrenormalization theorems, hints of supersymmetry, and perturbative stability will be discussed.
Primordial Magnetic Fields & Non-Gaussianity

Martin Sloth University of Southern Denmark
November 06, 2012

PIRSA:12110040
Astrophysics
There are indications of a lower bound on magnetic fields in the intergalactic media. Since magnetic fields on such large scales are difficult to generate in the late universe, this might point to inflationary magnetogenesis as the origin of intergalactic magnetic fields. If the magnetic fields are generated during inflation, they are naturally correlated with the inflaton perturbations in a general class of models. This leads to a consistency relation between the power spectrum of primordial magnetic fields and the non-Gaussian three-point cross-correlation of magnetic fields with the inflaton perturbation. The size of non-Gaussianity can be expressed in a new magnetic non-linearity parameter b_NL. In the flattened shape where the non-Gaussianity is maximal, b_NL can be as large as 5000.
Kicking Chameleons: Early Universe Challenges for Chameleon Gravity

Adrienne Erickcek University of North Carolina at Chapel Hill
October 25, 2012

PIRSA:12100125
Astrophysics
Chameleon gravity is a scalar-tensor theory that mimics general relativity in the Solar System. The scalar degree of freedom is hidden in high-density environments because the effective mass of the chameleon scalar depends on the trace of the stress-energy tensor. In the early Universe, when the trace of the stress-energy tensor is nearly zero, the chameleon is very light and Hubble friction prevents it from reaching its potential minimum. Whenever a particle species becomes non-relativistic, however, the trace of the stress-energy tensor is temporarily nonzero, and the chameleon begins to roll. I will show that these "kicks" to the chameleon field have catastrophic consequences for chameleon gravity. The velocity imparted to the chameleon is sufficiently large that the chameleon's mass changes rapidly as it slides past its potential minimum. This nonadiabatic process shatters the chameleon field by generating extremely high-energy perturbations, casting doubt on chameleon gravity's viability as an alternative to general relativity.
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 Koehn AI
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.
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.
Exoplanet observation by microlensing and wave optics features

Sohrab Rahvar Sharif University of Technology

August 14, 2012

PIRSA:12080006

I will introduce the theory and experimental technique of extra-solar planet observation by the gravitational microlensing and give a report on recent results. Then I will discuss the wave optics features in the gravitational microlensing, the analogy of this effect in the astronomical scales to the Young's double slit experiment. Finally I will discuss about the possibility of observation of diffraction patterns in the microlensing experiment.

Title	Speaker(s)	Date	Talk Type	Info
Recent progress on de Sitter S-matrix	Ian Morrison	2012-11-13	Scientific Series	View details
Primordial Magnetic Fields & Non-Gaussianity	Martin Sloth	2012-11-06	Scientific Series	View details
Kicking Chameleons: Early Universe Challenges for Chameleon Gravity	Adrienne Erickcek	2012-10-25	Scientific Series	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
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
Exoplanet observation by microlensing and wave optics features	Sohrab Rahvar	2012-08-14	Scientific Series	View details

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Cosmology and Gravitation

Format results

Recent progress on de Sitter S-matrix

Primordial Magnetic Fields & Non-Gaussianity

Kicking Chameleons: Early Universe Challenges for Chameleon Gravity

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

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

Exoplanet observation by microlensing and wave optics features

Recent progress on de Sitter S-matrix

Primordial Magnetic Fields & Non-Gaussianity

Kicking Chameleons: Early Universe Challenges for Chameleon Gravity

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

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

Exoplanet observation by microlensing and wave optics features