Cosmology and Gravitation

690 talks

S004

Collection TypeSeries

SubjectAstrophysics

Source RepositoryPIRSA

Displaying 361 - 372 of 690

The Case for an Alternative Cosmology

Jayant Narlikar IUCAA - The Inter-University Centre for Astronomy and Astrophysics
May 06, 2014

PIRSA:14050034
Astrophysics
Galileon Maps: Inequivalent Coset Constructions for Spacetime Symmetries

Gabirele Trevisan SISSA International School for Advanced Studies
April 29, 2014

PIRSA:14040132
Astrophysics
Groups and Clusters of Galaxies: Where Cosmology and Astrophysics Collide

Arif Babul University of Victoria
April 15, 2014

PIRSA:14040133
Astrophysics
Is the Milky Way Ringing?

Lawrence Widrow Queen's University
April 08, 2014

PIRSA:14040137
Astrophysics
The not-so-homogeneous universe

Phil Bull Queen Mary University of London
April 01, 2014

PIRSA:14040129
Astrophysics
Cosmic initial conditions and the CMB

Daniel Grin California Institute of Technology
March 25, 2014

PIRSA:14030112
Astrophysics
Inflation After Planck
March 18, 2014

PIRSA:14030116
Astrophysics
SDSS-III BOSS and Beyond: fundamental physics with galaxy redshift surveys

Beth Reid Lawrence Berkeley National Laboratory
March 11, 2014

PIRSA:14030096
Astrophysics
Cosmology Results from the Pan-STARRs Supernova Survey

Danial Scolnic Johns Hopkins University
March 04, 2014

PIRSA:14030095
Astrophysics
Probing the Small Scale Structure of Dark Matter with Indirect Detection

Sheldon Campbell Ohio State University
February 25, 2014

PIRSA:14020097
Astrophysics
Evolution of cosmological black holes: exact solutions, accretion and scalar fields

Daniel Guariento Conestoga College
February 18, 2014

PIRSA:14020150
Astrophysics
Our Lopsided Universe

Marina Cortes Institute for Astrophysics and Space Sciences
February 11, 2014

PIRSA:14020139
Astrophysics

The Case for an Alternative Cosmology

Jayant Narlikar IUCAA - The Inter-University Centre for Astronomy and Astrophysics
May 06, 2014

PIRSA:14050034
Astrophysics
This talk will describe the Quasi-Steady State Cosmology proposed in 1993 by Fred Hoyle, Geoffrey Burbidge and Jayant Narlikar. Starting with the motivation for this exercise, a formal field theoretic framework inspired by Mach’s principle is shown to lead to this model. The model is a generalization of the classical steady state model in the sense that it is driven by a scalar field which causes creation in explosive form. Such ‘minicreation events’ lead to a universe with a long term de Sitter expansion superposed with oscillations of shorter time scales. It is shown that this cosmology explains all the observed cosmological features and that there exist potential tests to distinguish between this cosmology and the standard big bang cosmology.
Galileon Maps: Inequivalent Coset Constructions for Spacetime Symmetries

Gabirele Trevisan SISSA International School for Advanced Studies
April 29, 2014

PIRSA:14040132
Astrophysics
Non-linear realizations of spacetime symmetries can be obtained by a generalization of the coset construction valid for internal ones. The physical equivalence of different representations for spacetime symmetries is not obvious, since their relation involves not only a redefinition of the fields but also a field-dependent change of coordinates. A simple and relevant spacetime symmetry is obtained by the contraction of the 4D conformal group that leads to the Galileon group. In this talk I will analyze two non-linear realizations of this group, focusing in particular on the propagation of signals around non-trivial backgrounds.
Groups and Clusters of Galaxies: Where Cosmology and Astrophysics Collide

Arif Babul University of Victoria
April 15, 2014

PIRSA:14040133
Astrophysics
Groups and clusters of galaxies are the most massive gravitationally bound objects in the Universe. They are also the most recent cosmic objects to form. In the currently accepted models of cosmic structure formation, the number density distribution of the most massive of these systems, and how this has been changing with time, depend sensitively to the parameters describing the large-scale geometry and the expansion history of the universe. However, to exploit galaxy clusters as cosmological probes, we must be able to relate their observable properties to their total mass. I will discuss our ongoing effort to calibrate the X-ray/SZ observations to the total mass for the 50 clusters comprising the Canadian Cluster Comparison Project (CCCP) sample. Resulting scaling relations, the associated scatter, and even how these change with time, invariably depend on "astrophysics" unfolding in these systems. The precision with which the cosmological parameters can be determined depends critically on how well we understand why groups and clusters manifest the observed properties that they do. This, however, has proven challenging. I will provide an update of the current state of affairs and highlight some of the key gaps in our understanding of the underlying physics.
Is the Milky Way Ringing?

Lawrence Widrow Queen's University
April 08, 2014

PIRSA:14040137
Astrophysics
Recent observations from three different astronomical surveys have revealed evidence for asymmetries about the Galactic midplane in the kinematics of solar neighborhood stars. These asymmetries appear, in part, as compression-rarefaction modes in the bulk motions of stars perpendicular to the midplane. I will discuss the hypothesis that these motions were caused by the recent passage of a satellite galaxy or dark matter subhalo through the Galactic disk. In short, we may be witnessing the early stages of a disk-heating event during which the Galaxy's disk relaxes to a new state after interacting with substructure from its own halo.
The not-so-homogeneous universe

Phil Bull Queen Mary University of London
April 01, 2014

PIRSA:14040129
Astrophysics
The assumption of spatial homogeneity lies at the heart of the concordance cosmological model. But as I will discuss, truly solid empirical evidence for global (statistical) homogeneity is lacking, and tricky theoretical issues abound. I review a few recent advances in understanding the role inhomogeneity plays in cosmology, including some unexpected effects on light propagation, the death (and rebirth) of backreaction, and impending observational annoyances related to the lumpy local Universe. I'll also talk about some near-future observations that can give us a handle on these effects
Cosmic initial conditions and the CMB

Daniel Grin California Institute of Technology
March 25, 2014

PIRSA:14030112
Astrophysics
One new frontier in cosmology is the frequency spectrum of the CMB. Future instruments may be precise enough to measure deviations from the nearly-perfect blackbody, measuring a chemical potential and thus probing energy injection at extremely high redshift. I will discuss ($\mu$ and $y$-type) CMB spectral distortions from the dissipation of entropy (isocurvature)-sourced acoustic modes. I will then discuss how a high-energy phase transition could also source such distortions. I will then switch gears and talk about the possibility of measuring a spatial fluctuation in the baryon/DM ratio using the CMB, including recent observational results. I may also muse on the surprising possible connection between these compensated isocurvature modes and the anomalously low large-scale scalar power hinted at by Planck observations of the CMB temperature power spectrum and the recent claimed BICEP2 detection of primordial tensor modes
Inflation After Planck
March 18, 2014

PIRSA:14030116
Astrophysics
The Planck satellite measurement of the cosmic microwave background has provided spectacular confirmation of the predictions of inflationary cosmology, putting inflation on a firm footing as the leading theory of the very early universe. I will discuss the implications of Planck for the simplest canonical single-field inflation models, which are favored by the data. Then I will discuss the most general question: How strong is the case that inflation is the "right" theory of the early universe?
SDSS-III BOSS and Beyond: fundamental physics with galaxy redshift surveys

Beth Reid Lawrence Berkeley National Laboratory
March 11, 2014

PIRSA:14030096
Astrophysics
The SDSS-III Baryon Oscillation Spectroscopic Survey, now nearly complete, is measuring the three-dimensional cosmic structure with 1.35 million new redshifts. Galaxy clustering measurements provide constraints on the cosmic expansion history through the baryon acoustic oscillation feature and the Alcock-Paczynski effect. In addition, the imprint of galaxy peculiar velocities on the observed galaxy clustering, "redshift-space distortions", provides a measurement of the growth rate of matter perturbations. Taken together, these measurements provide excellent constraints on dark energy and test the relation between expansion history and growth of perturbations expected in General Relativity. I will summarize results from BOSS's recent DR11 results and highlight what we may learn about fundamental physics (especially neutrinos) from the upcoming Dark Energy Spectroscopic Instrument (DESI).
Cosmology Results from the Pan-STARRs Supernova Survey

Danial Scolnic Johns Hopkins University
March 04, 2014

PIRSA:14030095
Astrophysics
The Pan-STARRs supernova survey has discovered one of the largest samples of Type Ia supernovae. Measurements of the distances to these supernovae allow us to probe some of the most fundamental questions about the properties of the universe like what is dark energy. When combining measurements from various astrophysical probes, we find hints of interesting tension with the Lambda-CDM model. I discuss the various combinations of astrophysical probes and the source of this tension. It is possible that this tension is due to systematic uncertainties in the various measurements, and I show how we analyze these uncertainties in the Pan-STARRs sample.
Probing the Small Scale Structure of Dark Matter with Indirect Detection

Sheldon Campbell Ohio State University
February 25, 2014

PIRSA:14020097
Astrophysics
Direct observation of the small scale structure of matter in the Universe provides potentially important information about a wealth of physics, from complex galaxy evolution processes to fundamental particle properties of dark matter. Detecting this fine structure in dark matter, though, is notoriously difficult. Dark matter indirect detection--through observation of radiation products of particle annihilation--may be the most direct method for observing small scale structure. However, in an observed signal, the amount of dark matter clustering is degenerate with the annihilation cross section. This talk outlines ways this degeneracy may be broken with indirect detection alone. Scenarios are discussed where either abundant substructure leads to discovery of annihilation radiation (revealing properties of the substructure), or a discovery strongly constrains the presence of significant dark matter halo substructure.
Evolution of cosmological black holes: exact solutions, accretion and scalar fields

Daniel Guariento Conestoga College
February 18, 2014

PIRSA:14020150
Astrophysics
Systems which contemplate the gravitational interaction between compact objects and the matter content in a cosmological environment constitute an important problem which has been studied since the early days of General Relativity. The generalized McVittie black hole is a simple exact solution to this problem, which provides us with insight on some of its known physical aspects, as well as hints to new mechanisms which arise from a formal treatment. We review some properties of this solution and its matter source, which can be interpreted as a classical fluid but is also an exact solution to a nontrivial scalar field theory.
Our Lopsided Universe

Marina Cortes Institute for Astrophysics and Space Sciences
February 11, 2014

PIRSA:14020139
Astrophysics
After a short introduction to open inflation and the observed large-scale cosmic microwave anomalies, which have been confirmed by the Planck satellite, I'll argue that the anomalies are naturally explained in the context of a marginally-open, negatively curved universe. I'll look in particular at the dipole power asymmetry, and motivate that this asymmetry can happen if our universe has bubble nucleated in a phase transition during a period of early inflation, and, as a result, has open geometry. Open inflation models, which are motivated by the string landscape and can excite `super-curvature' perturbation modes, can explain the presence of a very-large-scale perturbation, like the one we observe, which leads to a dipole modulation of the power spectrum. I'll provide a specific implementation of the scenario which is compatible with all existing constraints.

Title	Speaker(s)	Date	Talk Type	Info
The Case for an Alternative Cosmology	Jayant Narlikar	2014-05-06	Scientific Series	View details
Galileon Maps: Inequivalent Coset Constructions for Spacetime Symmetries	Gabirele Trevisan	2014-04-29	Scientific Series	View details
Groups and Clusters of Galaxies: Where Cosmology and Astrophysics Collide	Arif Babul	2014-04-15	Scientific Series	View details
Is the Milky Way Ringing?	Lawrence Widrow	2014-04-08	Scientific Series	View details
The not-so-homogeneous universe	Phil Bull	2014-04-01	Scientific Series	View details
Cosmic initial conditions and the CMB	Daniel Grin	2014-03-25	Scientific Series	View details
Inflation After Planck		2014-03-18	Scientific Series	View details
SDSS-III BOSS and Beyond: fundamental physics with galaxy redshift surveys	Beth Reid	2014-03-11	Scientific Series	View details
Cosmology Results from the Pan-STARRs Supernova Survey	Danial Scolnic	2014-03-04	Scientific Series	View details
Probing the Small Scale Structure of Dark Matter with Indirect Detection	Sheldon Campbell	2014-02-25	Scientific Series	View details
Evolution of cosmological black holes: exact solutions, accretion and scalar fields	Daniel Guariento	2014-02-18	Scientific Series	View details
Our Lopsided Universe	Marina Cortes	2014-02-11	Scientific Series	View details

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Cosmology and Gravitation

Format results

The Case for an Alternative Cosmology

Galileon Maps: Inequivalent Coset Constructions for Spacetime Symmetries

Groups and Clusters of Galaxies: Where Cosmology and Astrophysics Collide

Is the Milky Way Ringing?

The not-so-homogeneous universe

Cosmic initial conditions and the CMB

Inflation After Planck

SDSS-III BOSS and Beyond: fundamental physics with galaxy redshift surveys

Cosmology Results from the Pan-STARRs Supernova Survey

Probing the Small Scale Structure of Dark Matter with Indirect Detection

Evolution of cosmological black holes: exact solutions, accretion and scalar fields

Our Lopsided Universe

The Case for an Alternative Cosmology

Galileon Maps: Inequivalent Coset Constructions for Spacetime Symmetries

Groups and Clusters of Galaxies: Where Cosmology and Astrophysics Collide

Is the Milky Way Ringing?

The not-so-homogeneous universe

Cosmic initial conditions and the CMB

Inflation After Planck

SDSS-III BOSS and Beyond: fundamental physics with galaxy redshift surveys

Cosmology Results from the Pan-STARRs Supernova Survey

Probing the Small Scale Structure of Dark Matter with Indirect Detection

Evolution of cosmological black holes: exact solutions, accretion and scalar fields

Our Lopsided Universe