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 877 - 888 of 2166

TBA

Kipp Cannon University of Tokyo
June 15, 2016

PIRSA:16060013
Cosmology
What does the Advanced LIGO detection say about gravity?

Nicolas Yunes University of Illinois Urbana-Champaign
June 15, 2016

PIRSA:16060016
Cosmology
The Dynamical Strong-field Regime of General Relativity

Frans Pretorius Princeton University
June 15, 2016

PIRSA:16060015
Cosmology
Black hole ringdown and quasinormal modes

Aaron Zimmerman The University of Texas at Austin
June 15, 2016

PIRSA:16060014
Cosmology
Turbulent gravity in asymptotically AdS spacetimes

Stephen Green University of Nottingham
June 15, 2016

PIRSA:16060017
Cosmology
A new probe of primordial magnetic fields at high redshift

Vera Gluscevic University of Southern California
June 14, 2016

PIRSA:16060011
Cosmology
Inhomogeneous Anisotropic Cosmology

Leonardo Senatore ETH Zurich
June 14, 2016

PIRSA:16060010
Cosmology
The Classicality Puzzle

Jean-Luc Lehners Self Employed
June 14, 2016

PIRSA:16060009
Cosmology
A Dark Matter of Superfluid

Justin Khoury University of Pennsylvania
June 14, 2016

PIRSA:16060008
Cosmology
Dark matter phenomenology across cosmic times

Yacine Ali-Haimoud Johns Hopkins University
June 14, 2016

PIRSA:16060007
Cosmology
Parametrizing general linear cosmological perturbations

Macarena Lagos University of Chicago
June 02, 2016

PIRSA:16060001
Cosmology
Cosmology with BOSS

Anze Slosar Brookhaven National Laboratory
May 31, 2016

PIRSA:16050014
Cosmology

TBA

Kipp Cannon University of Tokyo
June 15, 2016

PIRSA:16060013
Cosmology
What does the Advanced LIGO detection say about gravity?

Nicolas Yunes University of Illinois Urbana-Champaign
June 15, 2016

PIRSA:16060016
Cosmology
The gravitational-wave observation GW150914 by Advanced LIGO provides the first opportunity to learn about theoretical physics mechanisms that may be present in the extreme gravity environment of coalescing binary black holes. The LIGO collaboration verified that this observation is consistent with Einstein's theory of General Relativity, constraining the presence of parametric anomalies in the signal. In this talk, I will discuss the plethora of additional inferences about gravity that can be drawn from the absence of such anomalies in the LIGO observation. I will focus and classify these inferences into those that inform us about the generation of gravitational waves (e.g. the activation of scalar fields, black hole graviton leakage into extra dimensions, the variability of Newton's constant, the breakage of Lorentz invariance and parity invariance), and the propagation of gravitational waves (e.g. the speed of gravity and the existence of large extra dimensions). I will conclude with a discussion of how these inferences may inform us about the models of modified gravity in cosmology.
The Dynamical Strong-field Regime of General Relativity

Frans Pretorius Princeton University
June 15, 2016

PIRSA:16060015
Cosmology
In this talk I will discuss some of the consequences for our understanding of strong-field gravity that can be gleaned from the recent detection of gravitational waves by the LIGO/Virgo collaboration. The event heard, GW150914, is consistent with the emission of gravitational waves from the late inspiral, merger and ringdown of two heavy stellar mass black holes. This has given us the first quantifiable pieces of evidence that the dynamics and properties of colliding black holes are governed by general relativity. At present certain exotic compact object alternatives to black holes within general relativity, such as boson stars or gravastars, cannot yet be ruled out due to lack of concrete predictions of the merger regime in such scenarios. However, I will argue that even if the progenitors of GW150914 where composed of such exotic matter, the gravitational wave data strongly suggests collision lead to the prompt formation of a Kerr black hole.
Black hole ringdown and quasinormal modes

Aaron Zimmerman The University of Texas at Austin
June 15, 2016

PIRSA:16060014
Cosmology
The first detection of gravitational waves came with an unexpected windfall: a clear signal from the merger of two black holes into a final, spinning black hole. General Relativity predicts that following merger, the final black hole relaxes by emitting radiation in a characteristic spectrum of decaying modes. I will discuss these ``quasinormal modes'' and what can be learned from them, as well as the black hole ringdown observed in GW150914. I will also explore the exotic side of ringdown, including the modes of nearly extremal black holes, and a tool for understanding the ringdown of black holes which differ from the standard Kerr solution.
Turbulent gravity in asymptotically AdS spacetimes

Stephen Green University of Nottingham
June 15, 2016

PIRSA:16060017
Cosmology
Dynamics in asymptotically anti-de Sitter spacetimes with reflecting boundary conditions are characterized by reduced dissipation as compared to asymptotically flat spacetimes. Such spacetimes, thus, represent opportunities to study nonlinear gravitational interactions that would otherwise be quickly damped away. I will discuss two background spacetimes---large AdS black branes in d=4, and pure AdS---where small perturbations display turbulent behavior and energy cascades driven by nonlinear interactions. In each case, the presence of an unexpected conserved quantity---a gravitational "enstrophy" around the AdS black brane, and a "particle number" for pure AdS perturbations---significantly affects the energy flow direction throughout the cascade, and drives energy to longer distance scales. I will comment on implications for fundamental general relativity questions such as cosmic censorship, and potential for turbulence beyond AdS.
A new probe of primordial magnetic fields at high redshift

Vera Gluscevic University of Southern California
June 14, 2016

PIRSA:16060011
Cosmology
I will present a novel method for probing extremely weak large-scale magnetic fields in the intergalactic medium prior to the epoch of reionization. This method relies on the effect of spin alignment of hydrogen atoms in a cosmological setting, and on the effect of magnetic precession of the atoms on the statistics of the 21–cm brightness–temperature fluctuations. It is intrinsically sensitive to magnetic fields weaker than 10^{-19} Gauss in physical units, and thus has a potential to reach many orders of magnitude below the current constraints on primordial magnetic fields. I will discuss the physical mechanism, lay out the estimator formalism that enables searches with future 21-cm tomographic surveys, and present forecasts for detecting magnetic fields in the high-redshift universe using this method.
Inhomogeneous Anisotropic Cosmology

Leonardo Senatore ETH Zurich
June 14, 2016

PIRSA:16060010
Cosmology
In homogeneous and isotropic Friedmann-Robertson-Walker cosmology, the topology of the universe determines its ultimate fate. If the Weak Energy Condition is satisfied, open and flat universes must expand forever, while closed cosmologies can recollapse to a Big Crunch. A similar statement holds for homogeneous but anisotropic (Bianchi) universes. Here, we prove that arbitrarily inhomogeneous and anisotropic cosmologies with ``flat'' (including toroidal) and ``open'' (including compact hyperbolic) spatial topology that are initially expanding must continue to expand forever at least in some region at a rate bounded from below by a positive number, despite the presence of arbitrarily large density fluctuations and/or the formation of black holes. Because the set of 3-manifold topologies is countable, a single integer determines the ultimate fate of the universe, and, in a specific sense, most 3-manifolds are ``flat'' or ``open''. Our result has important implications for inflation: if there is a positive cosmological constant (or suitable inflationary potential) and initial conditions for the inflaton, cosmologies with ``flat'' or ``open'' topology must expand forever in some region at least as fast as de Sitter space, and are therefore very likely to begin inflationary expansion eventually, regardless of the scale of the inflationary energy or the spectrum and amplitude of initial inhomogeneities and gravitational waves. Our result is also significant for numerical general relativity, which often makes use of periodic (toroidal) boundary conditions.
The Classicality Puzzle

Jean-Luc Lehners Self Employed
June 14, 2016

PIRSA:16060009
Cosmology
Why was the early universe classical? Along with the big bang singularity problem and the flatness, horizon and inhomogeneity puzzles, this is one of the big unexplained features of the hot big bang scenario. In this talk I will discuss how inflation and ekpyrosis, which have mainly been considered as models that can address some of the other puzzles, can both drive the early universe towards classicality. The remarkable aspect is that classicality is achieved via the intrinsic dynamics of inflation and ekpyrosis, without invoking decoherence.
A Dark Matter of Superfluid

Justin Khoury University of Pennsylvania
June 14, 2016

PIRSA:16060008
Cosmology
Dark matter phenomenology across cosmic times

Yacine Ali-Haimoud Johns Hopkins University
June 14, 2016

PIRSA:16060007
Cosmology
The nature of dark matter remains one of the most nagging problems in cosmology. In this talk I will discuss several existing or potential probes of dark matter. I will start with a well known hot dark matter, massive neutrinos, and discuss their effect on large-scale structure in the non-linear regime. I will then talk about the effect of dark matter interactions with standard model particles on the spectrum of the CMB and on 21cm fluctuations. I will conclude by discussing whether LIGO could have detected primordial-black-hole dark matter.
Parametrizing general linear cosmological perturbations

Macarena Lagos University of Chicago
June 02, 2016

PIRSA:16060001
Cosmology
We have great certainty on how gravity works around our solar system: General Relativity (GR) has been found to be very accurate at these small scales. On large scales though, we still have a considerable lack of understanding about the evolution of the universe, and its constituents. While the LCDM model is in good agreement with cosmological data, this might change in the future. For this reason, we need to test GR on these scales.

There are a number of proposals on how to characterize deviations from GR on larges scales, by parametrizing different cosmological evolutions of the universe - the PPF, EFT and EA approaches. The objective is to use experimental data to constrain these parameters, and thus identify the most accurate cosmological model. In this talk I will show an alternative, systematic and general, parametrization method, in which we construct the most general quadratic action for linear cosmological perturbations, given some field content and gauge symmetries. I will show the example of linearly diffeomorphism-invariant scalar-tensor theories, in which case the parametrization encompasses well-known theories such as Horndeski and Beyond Horndeski. The method can straightforwardly be applied to any gravity theory with any fields and gauge symmetries.
Cosmology with BOSS

Anze Slosar Brookhaven National Laboratory
May 31, 2016

PIRSA:16050014
Cosmology
I will discuss how we constrain properties of the universe using two
tracers of large scale structure measured by the BOSS (Baryon
Oscillations Spectroscopic Experiment): galaxies and Lyman-alpha
forest. I will show recent results from baryonic acoustic oscillations
measured in both tracers and discuss cosmological implications. I
will briefly mention other measurements and consider forecasts for
quasar-forest bispectrum to constrain primordial non-Gaussianity.

Title	Speaker(s)	Date	Talk Type	Info link
TBA	Kipp Cannon	2016-06-15	Conference	View details
What does the Advanced LIGO detection say about gravity?	Nicolas Yunes	2016-06-15	Conference	View details
The Dynamical Strong-field Regime of General Relativity	Frans Pretorius	2016-06-15	Conference	View details
Black hole ringdown and quasinormal modes	Aaron Zimmerman	2016-06-15	Conference	View details
Turbulent gravity in asymptotically AdS spacetimes	Stephen Green	2016-06-15	Conference	View details
A new probe of primordial magnetic fields at high redshift	Vera Gluscevic	2016-06-14	Conference	View details
Inhomogeneous Anisotropic Cosmology	Leonardo Senatore	2016-06-14	Conference	View details
The Classicality Puzzle	Jean-Luc Lehners	2016-06-14	Conference	View details
A Dark Matter of Superfluid	Justin Khoury	2016-06-14	Conference	View details
Dark matter phenomenology across cosmic times	Yacine Ali-Haimoud	2016-06-14	Conference	View details
Parametrizing general linear cosmological perturbations	Macarena Lagos	2016-06-02	Scientific Series	View details
Cosmology with BOSS	Anze Slosar	2016-05-31	Scientific Series	View details

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