Cosmology

Cosmologists at Perimeter Institute seek to help pin down the constituents and history of our universe, and the rules governing its origin and evolution. Many of the most interesting clues about physics beyond the standard model (e.g., dark matter, dark energy, the matter/anti-matter asymmetry, and the spectrum of primordial density perturbations], come from cosmological observations, and cosmological observations are often the best way to test or constrain a proposed modification of the laws of nature, since such observations can probe length scales, time scales, and energy scales that are beyond the reach of terrestrial laboratories.

Displaying 1165 - 1176 of 2144

Superhorizon fluctuations in de Sitter and cosmological spacetimes

Guilherme Pimentel Universiteit van Amsterdam
January 15, 2013

PIRSA:13010001
Quantum Fields and Strings

Cosmology
Parameterizing dark sector perturbations

Jonathan Pearson Durham University
January 15, 2013

PIRSA:13010019
Cosmology
Fifth forces and new particles from dark energy

Amol Upadhye University of Wisconsin–Madison
January 08, 2013

PIRSA:13010023
Cosmology
A robust constraint on cosmic textures from the cosmic microwave background

Stephen Feeney
December 11, 2012

PIRSA:12120034
Cosmology
Nonlinear Extensions for the Inflationary Power Spectra

Shun-Pei Miao Utrecht University
December 11, 2012

PIRSA:12120014
Cosmology
CMB as a Probe of New Physics: The Story of Cosmic Birefringence
December 06, 2012

PIRSA:12120019
Cosmology
Bubble Baryogenesis

Gilly Elor University of California, Berkeley
November 27, 2012

PIRSA:12110091
Cosmology
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
Massive gravitons, the cosmological constant and new directions in gravity
November 14, 2012

PIRSA:12110061
Cosmology

Superhorizon fluctuations in de Sitter and cosmological spacetimes

Guilherme Pimentel Universiteit van Amsterdam
January 15, 2013

PIRSA:13010001
Quantum Fields and Strings

Cosmology
I will discuss superhorizon fluctuations in de Sitter space. The first part of the talk will focus on computing entanglement entropies of field theories in a fixed de Sitter background. Those computations are done for free theories and also theories with gravity duals. If time permits, I will also discuss superhorizon fluctuations in cosmological backgrounds. In particular, I focus on showing that subhorizon fluctuations can not produce any significant backreaction on superhorizon modes. If those late time effects existed, one in principle could not trust the scale invariant spectrum of inflationary theories to be the source of the spectrum of thermal fluctuations of the CMB.
Parameterizing dark sector perturbations

Jonathan Pearson Durham University
January 15, 2013

PIRSA:13010019
Cosmology
When recent observational evidence and the GR+FRW+CDM model are combined we obtain the result that the Universe is accelerating, where the acceleration is due to some not-yet-understood "dark sector". There has been a considerable number of theoretical models constructed in an attempt to provide an "understanding" of the dark sector: dark energy and modified gravity theories. The proliferation of modified gravity and dark energy models has brought to light the need to construct a "generic" way to parameterize the dark sector. We will discuss our new way of approaching this problem, looking at linearised perturbations. Our approach is inspired by that taken in particle physics, where the most general modifications to the standard model are written down for a given field content that is compatible with some assumed symmetry (which we take to be isotropy of the background spatial sections). Our emphasis is on constructing a theoretically motivated toolkit which can be used to extract meaningful information about the dark sector (such as its field content). We find, for example, that the observational impact of very broad classes of theories can be encoded by a very small (less than 5) number of parameters. It is these parameters which we hope to measure with observational data.
Fifth forces and new particles from dark energy

Amol Upadhye University of Wisconsin–Madison
January 08, 2013

PIRSA:13010023
Cosmology
Dark energy coupled to Standard Model fermions and gauge bosons gives rise to fifth forces and new particles, which are readily accessible to experiments from laboratory to cosmological scales. I will discuss chameleon and symmetron models, whose fifth forces are screened locally through large effective masses and symmetry-restoring phase transitions, respectively. Fifth force experiments such as the Eot-Wash torsion balance will test chameleons with small quantum corrections and gravitation-strength fifth forces, as well as symmetrons with coupling energies just beyond the Standard Model scale. A dark energy coupling to electromagnetism would imply that photons passing through a magnetic field will oscillate into particles of dark energy, a phenomenon studied by afterglow experiments such as CHASE. After constraining dark energy using laboratory experiments, I proceed to astrophysical probes. Particles of a photon-coupled dark energy could be produced in the Sun and detected in magnetic helioscopes such as CAST, while fifth forces may alter the dynamics of variable stars and the growth of large-scale structure.
A robust constraint on cosmic textures from the cosmic microwave background

Stephen Feeney
December 11, 2012

PIRSA:12120034
Cosmology
Fluctuations in the cosmic microwave background (CMB) contain information which has been pivotal in establishing the current cosmological model. These data can also be used to test well-motivated additions to this model, such as cosmic textures. Textures are a type of topological defect that can be produced during a cosmological phase transition in the early universe, and which leave characteristic hot and cold spots in the CMB. We apply Bayesian methods to carry out an optimal test of the texture hypothesis, using full-sky data from the Wilkinson Microwave Anisotropy Probe. We conclude that current data do not warrant augmenting the standard cosmological model with textures. We rule out at 95% confidence models that predict more than 6 detectable cosmic textures on the full sky.
Nonlinear Extensions for the Inflationary Power Spectra

Shun-Pei Miao Utrecht University
December 11, 2012

PIRSA:12120014
Cosmology
We expound several principles in an attempt to clarify the debate over infrared loop corrections to the primordial scalar and tensor power spectra from inflation. Among other things we note that existing proposals for nonlinear extensions of the scalar fluctuation field $\zeta$ introduce new ultraviolet divergences which no one understands how to renormalize. Loop corrections and higher correlators of these putative observables would also be enhanced by inverse powers of the slow roll parameter $\epsilon$. We propose an extension which might be better behaved.
CMB as a Probe of New Physics: The Story of Cosmic Birefringence
December 06, 2012

PIRSA:12120019
Cosmology
Cosmological birefringence is a postulated rotation of the linear polarization of photons that arises due to a Chern-Simons coupling of a new scalar field to electromagnetism. In particular, it appears as a generic feature of simple quintessence models for Dark Energy, and therefore, should it be detected, could provide insight into the microphysics of cosmic acceleration. Prior work has sought this rotation, assuming the rotation angle to be uniform across the sky, by looking for the parity-violating TB and EB correlations in the CMB temperature/polarization. However, if the scalar field that gives rise to cosmological birefringence has spatial fluctuations, then the rotation angle may vary across the sky. In this talk, I will present the results of the first CMB-based search for direction-dependent cosmological birefringence, using WMAP-7 data, and report the constraint on the rotation-angle power spectrum for all multipoles up to the resolution of the instrument. I will discuss the implications for a specific models for rotation, and show forecasts for Planck and future experiments. I will then conclude with a brief discussion of other exotic physical models, such as chiral gravity, and astrophysical scenarios, such as inhomogeneous reionization, that can be probed using the same analysis.
Bubble Baryogenesis

Gilly Elor University of California, Berkeley
November 27, 2012

PIRSA:12110091
Cosmology
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
Massive gravitons, the cosmological constant and new directions in gravity
November 14, 2012

PIRSA:12110061
Cosmology
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.

Title	Speaker(s)	Date	Talk Type	Info link
Superhorizon fluctuations in de Sitter and cosmological spacetimes	Guilherme Pimentel	2013-01-15	Scientific Series	View details
Parameterizing dark sector perturbations	Jonathan Pearson	2013-01-15	Scientific Series	View details
Fifth forces and new particles from dark energy	Amol Upadhye	2013-01-08	Scientific Series	View details
A robust constraint on cosmic textures from the cosmic microwave background	Stephen Feeney	2012-12-11	Scientific Series	View details
Nonlinear Extensions for the Inflationary Power Spectra	Shun-Pei Miao	2012-12-11	Scientific Series	View details
CMB as a Probe of New Physics: The Story of Cosmic Birefringence		2012-12-06	Scientific Series	View details
Bubble Baryogenesis	Gilly Elor	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
Massive gravitons, the cosmological constant and new directions in gravity		2012-11-14	Scientific Series	View details

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