Cosmology and Gravitation

Displaying 409 - 420 of 688

Holographic description of cosmological singularity

Misha Smolkin Hebrew University of Jerusalem
January 22, 2013

PIRSA:13010111
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
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

Holographic description of cosmological singularity

Misha Smolkin Hebrew University of Jerusalem
January 22, 2013

PIRSA:13010111
Cosmology
In my talk I will discuss our recent paper hep-th/1211.1322 where we construct a 3D conformal field theory dual to asymptotically AdS cosmology in four dimensions. Due to the scale invariance this dual theory allows an infinite family of instantons each of which breaks the conformal group O(3,2) down to O(3,1). These instantons are dual to bulk instantons responsible for nucleating an O(3,1) invariant cosmological bubble. Presumably they indicate an infinite instability rate, however we are able to sum over all of them completely. The resulting theory is manifestly stable, unitary and finite.
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.
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.

Title	Speaker(s)	Date	Talk Type	Info
Holographic description of cosmological singularity	Misha Smolkin	2013-01-22	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
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

Cosmology and Gravitation

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