Astrophysics

Displaying 1165 - 1176 of 2134

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

Solomon Endlich Stanford University
November 15, 2012

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

John Moffat Perimeter Institute for Theoretical Physics
November 14, 2012

PIRSA:12110074
Astrophysics
Massive gravitons, the cosmological constant and new directions in gravity
November 14, 2012

PIRSA:12110061
Astrophysics
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
12/13 PSI Researcher Presentation

Matthew Johnson York University
October 24, 2012

PIRSA:12100050
Astrophysics
Cosmological Constant
- Ivan Arraut University of Saint Joseph
- Stephon Alexander Brown University
- Alejandro Satz
- Maïté Dupuis Perimeter Institute for Theoretical Physics
- Antonino Marciano Fudan University
October 23, 2012

PIRSA:12100126
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
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

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

Solomon Endlich Stanford University
November 15, 2012

PIRSA:13010005
Astrophysics
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
Astrophysics
Massive gravitons, the cosmological constant and new directions in gravity
November 14, 2012

PIRSA:12110061
Astrophysics
The solutions to the cosmological constant problems may involve modifying the very long-range dynamics of gravity by adding new degrees of freedom. As an example of a conservative and minimal such modification, we consider the possibility that the graviton has a very small mass. Massive gravity has received renewed interest due to recent advances which have resolved its traditional problems. This kind of modification has some peculiar and unexpected features, and it points us towards a universe which looks quite unfamiliar.
Support for this colloquium is provided by The Templeton Frontiers Program.
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.
12/13 PSI Researcher Presentation

Matthew Johnson York University
October 24, 2012

PIRSA:12100050
Astrophysics
Cosmological Constant
- Ivan Arraut University of Saint Joseph
- Stephon Alexander Brown University
- Alejandro Satz
- Maïté Dupuis Perimeter Institute for Theoretical Physics
- Antonino Marciano Fudan University
October 23, 2012

PIRSA:12100126
Astrophysics
Dark Matter and Dark Energy as a Possible Manifestation of a Fundamental Scale
If we take the idea of the Planck length as a fundamental (minimum) scale and if additionally we impose the Cosmological Constant ($Lambda$) as and infrared (IR) cut-off parameter. Then it is possible to demonstrate that Dark Matter effects can emerge as a consequence of an IR-UV mix effect. This opens the possibility of unifying the Dark Energy and Dark matter effects in a single approach.

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Geometric Operators in Loop Quantum Gravity with a Cosmological Constant
Loop quantum gravity is a candidate to describe the quantum gravity regime with zero cosmological constant. One of its key results is that geometric operators such as area angle volume are quantized. Not much is known when the cosmological constant is not zero. It is usually believed that to introduce this parameter in the game we need to use quantum groups. However due to the complicated algebraic structure inherent to quantum groups the geometric operators are not yet properly defined (except the area operator). I will discuss how the use of tensor operators can circumvent the difficulties and allow to construct a natural set of observables. In particular I will construct the natural geometric observables such as angle or volume and discuss some of their implications.

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Interplay Between Cosmological Constant and DSR Scale
I offer brief remarks on several ways in which the cosmological constant could provide a clue toward quantum gravity. I then focus on how DSR-relativistic theories can be made compatible with spacetime expansion (possibly cosmological-constant-governed spacetime expansion), and how this interplay could manifest itself in data.

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Quantum Gravity RG Flow: A Cosmological Limit Cycle
I will discuss evidence for the existence of a limit cycle in the renormalization group for quantum gravity which is visible in a minisuperspace approximation. The emergence of the limit cycle can be studied through a tuning parameter representing the number of dimensions in which fluctuations of the conformal factor are suppressed. At the critical value of the tuning parameter all RG trajectories reaching the UV fixed point have an extended semiclassical regime with a small positive cosmological constant providing a possible model for a viable cosmology without fine-tuning.
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.

Title	Speaker(s)	Date	Talk Type	Info link
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
Massive gravitons, the cosmological constant and new directions in gravity		2012-11-14	Scientific Series	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
12/13 PSI Researcher Presentation	Matthew Johnson	2012-10-24	Course	View details
Cosmological Constant	Ivan Arraut, Stephon Alexander, Alejandro Satz, Maïté Dupuis, Antonino Marciano	2012-10-23	Conference	View details
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

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

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

Massive gravitons, the cosmological constant and new directions in gravity

Recent progress on de Sitter S-matrix

Primordial Magnetic Fields & Non-Gaussianity

Kicking Chameleons: Early Universe Challenges for Chameleon Gravity

12/13 PSI Researcher Presentation

Cosmological Constant

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

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

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

Massive gravitons, the cosmological constant and new directions in gravity

Recent progress on de Sitter S-matrix

Primordial Magnetic Fields & Non-Gaussianity

Kicking Chameleons: Early Universe Challenges for Chameleon Gravity

12/13 PSI Researcher Presentation

Cosmological Constant

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