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 1093 - 1104 of 2144

holographic path to the turbulent side of gravity
- Adam Brown Stanford University
- Stephen Green University of Nottingham
December 12, 2013

PIRSA:13120066
Cosmology
Partially Massless Gravity
December 11, 2013

PIRSA:13120005
Cosmology
Consistency of Massive Gravity

Lavinia Heisenberg ETH Zurich
December 10, 2013

PIRSA:13120061
Cosmology
Compactifying de Sitter

Alex Dahlen Princeton University
December 10, 2013

PIRSA:13120049
Cosmology
Supersymmetry, Non-thermal Dark Matter and Precision Cosmology

Scott Watson Syracuse University
December 05, 2013

PIRSA:13120054
Cosmology
Acceleration, Then and Now

Cliff Burgess McMaster University
December 03, 2013

PIRSA:13120059
Cosmology
BiGravity: from Cosmological Solutions to Dual Galileons

Matteo Fasiello University of Portsmouth
November 26, 2013

PIRSA:13110093
Cosmology
N-body lensed CMB maps: lensing extraction and characterization

Claudia Antolini SISSA International School for Advanced Studies
November 15, 2013

PIRSA:13110088
Cosmology
Is there evidence for additional neutrino species from cosmology?

Stephen Feeney
November 12, 2013

PIRSA:13110083
Cosmology
New Constraints on the Amplitude of Cosmic Density Fluctuations and Intracluster Gas from the Thermal SZ Signal Measured by Planck and ACT
November 11, 2013

PIRSA:13110081
Cosmology
Staring into the Abyss

Avery Broderick University of Waterloo
November 06, 2013

PIRSA:13110064
Cosmology

Strong Gravity
Feedback-regulated star formation on galactic and cosmological scales

Claude-André Faucher-Giguère University of California, Berkeley
November 05, 2013

PIRSA:13110056
Cosmology

holographic path to the turbulent side of gravity
- Adam Brown Stanford University
- Stephen Green University of Nottingham
December 12, 2013

PIRSA:13120066
Cosmology
We study the dynamics of a 2+1 dimensional relativistic viscous conformal fluid in Minkowski spacetime. Such fluid solutions arise as duals, under the "gravity/fluid correspondence", to 3+1 dimensional asymptotically anti-de Sitter (AAdS) black brane solutions to the Einstein equation. We examine stability properties of shear flows, which correspond to hydrodynamic quasinormal modes of the black brane. We find that, for sufficiently high Reynolds number, the solution undergoes an inverse turbulent cascade to long wavelength modes. We then map this fluid solution, via the gravity/fluid duality, into a bulk metric. This suggests a new and interesting feature of the behavior of perturbed AAdS black holes and black branes, which is not readily captured by a standard quasinormal mode analysis. Namely, for sufficiently large perturbed black objects (with long-lived quasinormal modes), nonlinear effects transfer energy from short to long wavelength modes via a turbulent cascade within the metric perturbation. As long wavelength modes have slower decay, this lengthens the overall lifetime of the perturbation. We also discuss various implications of this behavior, including expectations for higher dimensions, and the possibility of predicting turbulence in more general gravitational scenarios."
Partially Massless Gravity
December 11, 2013

PIRSA:13120005
Cosmology
On de Sitter space, there exists a special value for the mass of a graviton for which the linear theory propagates 4 rather than 5 degrees of freedom. If a fully non-linear version of the theory exists and can be coupled to known matter, it would have interesting properties and could solve the cosmological constant problem. I will describe evidence for and obstructions to the existence of such a theory.
Consistency of Massive Gravity

Lavinia Heisenberg ETH Zurich
December 10, 2013

PIRSA:13120061
Cosmology
Recently there has been a successful non-linear covariant ghost-free generalization of Fierz-Pauli massive gravity theory, the dRGT theory. I will explore the cosmology in the decoupling limit of this theory. Furthermore, I will construct a Proxy theory to dRGT from the decoupling limit and study the cosmology there as well and compare the results. Finally, I will discuss the quantum consistency of the theory.
Compactifying de Sitter

Alex Dahlen Princeton University
December 10, 2013

PIRSA:13120049
Cosmology
TBA
Supersymmetry, Non-thermal Dark Matter and Precision Cosmology

Scott Watson Syracuse University
December 05, 2013

PIRSA:13120054
Cosmology
Within the Minimal Supersymmetric Standard Model (MSSM), LHC bounds suggest that scalar superpartner masses are far above the electroweak scale. Given a high superpartner mass, nonthermal dark matter is a viable alternative to WIMP dark matter generated via freezeout. In the presence of moduli fields nonthermal dark matter production is associated with a long matter dominated phase, modifying the spectral index and primordial tensor amplitude relative to those in a thermalized primordial universe. Nonthermal dark matter can have a higher self-interaction cross-section than its thermal counterpart, enhancing astrophysical bounds on its annihilation signals. I will review recent progress in this program, and discuss how we can constrain the contributions to the neutralino mass from the bino, wino and higgsino using existing astrophysical bounds and direct detection experiments for models with nonthermal neutralino dark matter. Using these constraints we will then see how expected changes to inflationary observables result from the nonthermal phase.
Acceleration, Then and Now

Cliff Burgess McMaster University
December 03, 2013

PIRSA:13120059
Cosmology
There is good evidence that the universe underwent an epoch of accelerated expansion sometime in its very early history, and that it is entering a similar phase now. This talk is in two parts. The first part describes what I believe to be the take-home message about inflationary models, coming both from the recent Planck results and from attempts to embed inflation within a UV completion (string theory). I will argue that both point to a particularly interesting class of inflationary models that also evade many of the tuning problems of inflation. These models also turn out to make the tantalizing prediction that the scalar-to-tensor ratio, r, could be just out of reach, being predicted to be proportional to (n_s - 1)^2, where n_s ~ 0.96 is the spectral tilt of the scalar spectrum. The second part provides an update on an approach to solving the "cosmological constant problem", which asks why the vacuum energy seems to gravitate so little. This is the main theoretical obstruction that makes it so difficult to understand the origins of the present epoch of acceleration. In the approach described - Supersymmetric Large Extra Dimensions - observations can be reconciled with a large vacuum energy because the vacuum energy curves the extra dimensions and not the ones measured in cosmology. It leads to a picture of very supersymmetric gravity sector coupled to a completely non-supersymmetric particle-physics sector (which predicts in particular no superpartners to be found at the LHC). The update presented here summarizes the underlying mechanism whereby supersymmetry in the extra dimensions acts to suppress the gravitational effects of quantum fluctuations. Because the large quantum contributions are under control it becomes possible to estimate the size of to be expected of the observed dark energy. For the simplest configuratin the result is of order C (m Mg/4 pi Mp)^4, where m is the heaviest particle on the branes (and so no smaller than the top quark mass), Mg is the extra-dimensional gravity scale (no smaller than 10 TeV due to astrophysical constraints, implying two extra dimensions that are of order a micron in size) and Mp is the 4D Planck mass. C is a constant unsuppressed by symmetry-breaking effects, and C = 6 x 10^6 gives the observed dark energy density, using the smallest values given above for m and Mg. If there is time I will sketch arguments as to why there must be other light degrees of freedom in the theory as well, whose implications might ultimately be used to test the picture.
BiGravity: from Cosmological Solutions to Dual Galileons

Matteo Fasiello University of Portsmouth
November 26, 2013

PIRSA:13110093
Cosmology
I will present Cosmological FRW Solutions in BiGravity Theories and discuss their stability. After deriving the stability bound, one realizes that in Bigravity (in contradistinction to the FRW massive gravity case) the tension between requirements stemming from stability and those set by observations is resolved. The stability bound can also be derived in the decoupling limit of Bigravity. In this context an intriguing duality between Galilean interactions has emerged.
N-body lensed CMB maps: lensing extraction and characterization

Claudia Antolini SISSA International School for Advanced Studies
November 15, 2013

PIRSA:13110088
Cosmology
After multiple high precision detections (ACT, SPT, Planck) gravitational lensing has become a new source of relevant cosmological information: combining it with other probes (e.g. the large scale structure) can give significant insight on the evolution of the Dark Energy component. Developing new algorithms of estimate of this signal will allow the community to exploit this observable as a new and independent probe in cosmology. In my talk I will present the reconstruction of the lensing shear pattern and its angular power spectrum from total intensity and polarised CMB maps obtained using Born approximated ray-tracing through N-body simulated structures.The recovered spectra are in agreement with predictions of the underlying ΛCDM with no visible bias, on a scale interval which extends from the arcminute to several degrees over the sky. This demonstrates the feasibility of CMB lensing studies based on large scale simulations of cosmological structure formation in the context of the upcoming large observational campaigns.
Is there evidence for additional neutrino species from cosmology?

Stephen Feeney
November 12, 2013

PIRSA:13110083
Cosmology
It has been suggested that recent cosmological and flavor-oscillation data favor the existence of additional neutrino species beyond the three standard flavors. We apply Bayesian model selection to determine whether there is any evidence from current cosmological datasets for the standard cosmological model to be extended to include additional neutrino flavors. The datasets employed include cosmic microwave background temperature, polarization and lensing data, and measurements of the baryon acoustic oscillation scale and the Hubble constant. We also consider other additional neutrino physics, such as massive neutrinos, and possible degeneracies with other cosmological parameters.
New Constraints on the Amplitude of Cosmic Density Fluctuations and Intracluster Gas from the Thermal SZ Signal Measured by Planck and ACT
November 11, 2013

PIRSA:13110081
Cosmology
Galaxy clusters form from the rarest peaks in the initial matter distribution, and hence are a sensitive probe of the amplitude of density fluctuations (sigma_8), the amount of matter in the universe, and the growth rate of structure. Galaxy clusters have the potential to constrain dark energy and neutrino masses. However, cluster cosmology is currently limited by systematic uncertainties due to poorly understood intracluster gas physics. I will present new statistical approaches to understand clusters and improve their cosmological constraining power through the thermal Sunyaev-Zel'dovich (tSZ) effect. First, I will describe a forthcoming first detection of the cross-correlation of the tSZ signal reconstructed from Planck data with the large-scale matter distribution traced by the Planck CMB lensing potential. This statistic measures the amount of hot gas found in moderately massive groups and clusters (M ~ 10^13-10^14.5 M_sun), a mass scale below that probed by direct cluster detections. Second, I will describe the first measurement of the PDF of the tSZ field using ACT 148 GHz maps. This measurement contains information from all (zero-lag) moments of the tSZ field, beyond simply the 2- or 3-point functions. It is a very sensitive probe of sigma_8 and may also provide a method with which to break the degeneracy between sigma_8 and uncertainties in the physics of the intracluster gas.
Staring into the Abyss

Avery Broderick University of Waterloo
November 06, 2013

PIRSA:13110064
Cosmology

Strong Gravity
Nearly a century after their discovery, black holes remain one of the most striking, and problematic predictions of general relativity. Even more unsettling is the fact that they actually appear to exist! With only a handful of exceptions, every galaxy contains a supermassive behemoth, millions to billions as massive as the sun, at their center. These supermassive black holes are hardly incidental, they gravitationally power enormous outflows that rule the fates of their hosts. Despite the critical role they play in our understanding of gravity and impact upon the visible universe, actually testing their nature has remained beyond our reach - until now. Dr. Broderick will describe how astronomers are currently constructing (and operating) facilities that will image the horizons of black holes, and what we can already say about these enigmatic monsters in the dark.
Feedback-regulated star formation on galactic and cosmological scales

Claude-André Faucher-Giguère University of California, Berkeley
November 05, 2013

PIRSA:13110056
Cosmology
A central problem in galaxy formation is to understand why star formation is so inefficient. Within individual galaxies, gas is converted into stars at a rate two orders of magnitude slower than unimpeded gravitational collapse predicts, a fact embodied in the low normalization of the observed Kennicutt-Schmidt (K-S) relationship between star formation rate surface density and gas surface density. Star formation in galaxies is also globally inefficient in the sense that the stellar mass in dark matter halos is a small fraction of the universal baryon fraction. I will show that these two facts can be explained by the self-regulation of star formation by feedback from massive stars. Within galaxies, stellar feedback drives turbulence that supports the interstellar medium against collapse and the K-S law is set by the low strength of gravity relative to stellar feedback. The energy input from the same stellar feedback processes drive powerful galactic outflows that remove most of the gas accreted from the intergalactic medium before it has time to turn into stars. Using cosmological hydrodynamical simulations from our FIRE project ("Feedback In Realistic Environments"), I will show that gas removal by star formation-driven galactic winds successfully explains the observed galaxy stellar mass function, at least for galaxies less massive than the Milky Way. Feedback from massive black holes may be required to explain the quenching of more massive galaxies. Motivated by recent observations, I will discuss the physics of galactic winds driven by active galactic nuclei.

Title	Speaker(s)	Date	Talk Type	Info link
holographic path to the turbulent side of gravity	Adam Brown, Stephen Green	2013-12-12	Scientific Series	View details
Partially Massless Gravity		2013-12-11	Scientific Series	View details
Consistency of Massive Gravity	Lavinia Heisenberg	2013-12-10	Scientific Series	View details
Compactifying de Sitter	Alex Dahlen	2013-12-10	Scientific Series	View details
Supersymmetry, Non-thermal Dark Matter and Precision Cosmology	Scott Watson	2013-12-05	Scientific Series	View details
Acceleration, Then and Now	Cliff Burgess	2013-12-03	Scientific Series	View details
BiGravity: from Cosmological Solutions to Dual Galileons	Matteo Fasiello	2013-11-26	Scientific Series	View details
N-body lensed CMB maps: lensing extraction and characterization	Claudia Antolini	2013-11-15	Scientific Series	View details
Is there evidence for additional neutrino species from cosmology?	Stephen Feeney	2013-11-12	Scientific Series	View details
New Constraints on the Amplitude of Cosmic Density Fluctuations and Intracluster Gas from the Thermal SZ Signal Measured by Planck and ACT		2013-11-11	Scientific Series	View details
Staring into the Abyss	Avery Broderick	2013-11-06	Public Lectures	View details
Feedback-regulated star formation on galactic and cosmological scales	Claude-André Faucher-Giguère	2013-11-05	Scientific Series	View details

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