Cosmology and Gravitation

694 talks

S004

Collection TypeSeries

SubjectCosmology

Displaying 421 - 432 of 694

Mass and Tension (momentum) Sum Rules in AdS (dS)

Jennie Traschen University of Massachusetts Amherst
November 27, 2012

PIRSA:12110042
Quantum Gravity
Holography for inflation using conformal perturbation theory.

Paul McFadden Durham University
November 22, 2012

PIRSA:12110078
Cosmology
An exact solution of the Dirac equation with CP violation.

Tomislav Prokopec Utrecht University
November 20, 2012

PIRSA:12110076
Cosmology
Solid of Inflation: An alternative symmetry breaking pattern for an EFT of inflation

Solomon Endlich Stanford University
November 15, 2012

PIRSA:13010005
Cosmology
Modified Gravity, Dark Matter and Dark Energy: Deep Mysteries of the Universe

John Moffat Perimeter Institute for Theoretical Physics
November 14, 2012

PIRSA:12110074
Cosmology
Recent progress on de Sitter S-matrix

Ian Morrison West Chester University
November 13, 2012

PIRSA:12110043
Cosmology
Primordial Magnetic Fields & Non-Gaussianity

Martin Sloth University of Southern Denmark
November 06, 2012

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

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

PIRSA:12100125
Cosmology
Maximum entropy, the universal dark matter density profile... and its destruction

Andrew Pontzen University of Oxford
October 16, 2012

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

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

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

Jean-Luc Lehners Self Employed
October 09, 2012

PIRSA:12100042
Cosmology
Homogeneous and Isotropic Universe from Nonlinear Massive Gravity

A. Emir Gumrukcuoglu
October 02, 2012

PIRSA:12100002
Cosmology

Mass and Tension (momentum) Sum Rules in AdS (dS)

Jennie Traschen University of Massachusetts Amherst
November 27, 2012

PIRSA:12110042
Quantum Gravity
The stress-energy tensor in a conformal field theory has zero trace. Hence AdS boundary stress-tensors are traceless by construction, to match this property of the dual CFT. An elegant (aka nifty) construction based on the conformal isometry of AdS will be presented which shows that in an asymptotically AdS spacetime, the sum of the ADM mass and the ADM tensions is zero. This result follows strictly from the gravitational point of view- that is, the Einstein equations and the definitions of the ADM charges. Further, it turns out that perturbative stress-energy sources in an asymptotically AdS spacetime must satisfy a local version of this constraint, namely that the sum of the energy density minus the pressures equals zero. The situation with positive cosmological constant is both similar and distinct in interesting ways, which will be briefly discussed. The analogous (analytically continued) conformal isometry in dS is the root of the ``k^4 “ power spectrum for causal cosmological perturbations. Work in progress (speculations) will be presented about a corresponding sum-rule for gravitational charges defined at future infinity in a spacetime that approaches dS at late times.
Holography for inflation using conformal perturbation theory.

Paul McFadden Durham University
November 22, 2012

PIRSA:12110078
Cosmology
Holographic cosmology maps cosmological time evolution to the inverse RG ﬂow of a dual three-dimensional QFT. In cases where this RG ﬂow connects two closely separated ﬁxed points, QFT correlators may be calculated perturbatively in terms of the conformal ﬁeld theory associated with one of the ﬁxed points, even when the dual QFT is at strong coupling. Realising slow-roll inﬂation in these terms, we show how to derive standard slow-roll inﬂationary power spectra and non-Gaussianities through purely holographic calculations. The form of slow-roll inﬂationary correlators is seen to be determined by the perturbative breaking of conformal symmetry away from the ﬁxed point.
An exact solution of the Dirac equation with CP violation.

Tomislav Prokopec Utrecht University
November 20, 2012

PIRSA:12110076
Cosmology
After a brief overview of electroweak baryogenesis, I will show how to construct a solution of the Dirac equation for a CP violating kink wall. This solution nicely reduces to the known solution for a CP violating thin (step) wall. The novel solution can be helpful for studies of baryogenesis sources at strong first order phase transitions, which is relevant for electroweak scale baryogenesis studies.
Solid of Inflation: An alternative symmetry breaking pattern for an EFT of inflation

Solomon Endlich Stanford University
November 15, 2012

PIRSA:13010005
Cosmology
In this talk I will discuss a cosmological model where primordial inflation is driven by a `solid', defined as a system of three derivatively coupled scalar fields obeying certain symmetries and spontaneously breaking a certain subgroup of these. The symmetry breaking pattern differs drastically from that of standard inflationary models: time translations are unbroken. This prevents our model from fitting into the standard effective field theory description of adiabatic perturbations. Consequently, it exhibits a novel non-Gaussian `shape'.
Modified Gravity, Dark Matter and Dark Energy: Deep Mysteries of the Universe

John Moffat Perimeter Institute for Theoretical Physics
November 14, 2012

PIRSA:12110074
Cosmology
Recent progress on de Sitter S-matrix

Ian Morrison West Chester University
November 13, 2012

PIRSA:12110043
Cosmology
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
Cosmology
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
Cosmology
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
Cosmology
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
Cosmology
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
Cosmology
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
Cosmology
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.

Title	Speaker(s)	Date	Talk Type	Info
Mass and Tension (momentum) Sum Rules in AdS (dS)	Jennie Traschen	2012-11-27	Scientific Series	View details
Holography for inflation using conformal perturbation theory.	Paul McFadden	2012-11-22	Scientific Series	View details
An exact solution of the Dirac equation with CP violation.	Tomislav Prokopec	2012-11-20	Scientific Series	View details
Solid of Inflation: An alternative symmetry breaking pattern for an EFT of inflation	Solomon Endlich	2012-11-15	Scientific Series	View details
Modified Gravity, Dark Matter and Dark Energy: Deep Mysteries of the Universe	John Moffat	2012-11-14	Other	View details
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

Cosmology and Gravitation

Format results