Cosmology and Gravitation

692 talks

S004

Collection TypeSeries

SubjectCosmology

Displaying 385 - 396 of 692

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
Feedback-regulated star formation on galactic and cosmological scales

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

PIRSA:13110056
Cosmology
Aspects of Modified Gravity

Jeremy Sakstein University of Pennsylvania
October 31, 2013

PIRSA:13100132
Cosmology
Mapping Mass Across The Sky: CMB Lensing Measurements Past and Future

Blake Sherwin Princeton University
October 29, 2013

PIRSA:13100075
Cosmology
Conformal symmetry and cosmology

Austin Joyce University of Chicago
October 22, 2013

PIRSA:13100070
Cosmology
Hybrid quantization of the Gowdy model within loop quantum cosmology

Mercedes Martin-Benito Complutense University of Madrid
October 15, 2013

PIRSA:13100102
Cosmology
Einstein and the Fugu

Andrew Waldron University of California, Davis
October 10, 2013

PIRSA:13100101
Cosmology
A Nearly Gaussian Hubble-patch in a non-Gaussian Universe

Marilena LoVerde University of Washington
October 08, 2013

PIRSA:13100076
Cosmology

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.
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.
Aspects of Modified Gravity

Jeremy Sakstein University of Pennsylvania
October 31, 2013

PIRSA:13100132
Cosmology
In this talk I will give an introduction to some of my research into modified gravity over the last three years. I will begin by describing my implementation of chameleon models into supersymmetry and discuss some of the new features and cosmology that arise in this formalism. I will then change direction and talk about my work using astrophysical effects as novel probes of modified gravity theories and present some new results on modified gravity stellar oscillation theory. I will end by discussing work in progress and the possible future constraints that could be placed.
Mapping Mass Across The Sky: CMB Lensing Measurements Past and Future

Blake Sherwin Princeton University
October 29, 2013

PIRSA:13100075
Cosmology
Measurements of gravitational lensing in the Cosmic Microwave Background (CMB) directly probe the projected distribution of dark matter out to high redshifts. The CMB lensing maps thus encode a wealth of information about both fundamental physics (e.g., dark energy and neutrino properties) and high-redshift astrophysics. I will illustrate this by first reviewing measurements of CMB lensing with the Atacama Cosmology Telescope, discussing both CMB lensing auto-correlations and cross-correlations with quasars, galaxies and optical lensing. I will then discuss ongoing and upcoming measurements of CMB polarization lensing with the POLARBEAR and ACTPol experiments and explain the great scientific potential of such polarization lensing studies in the very near future.
Conformal symmetry and cosmology

Austin Joyce University of Chicago
October 22, 2013

PIRSA:13100070
Cosmology
We will explore the role that conformal symmetries may play in cosmology. First, we will discuss the symmetries underlying the statistics of the primordial perturbations which seeded the temperature anisotropies of the Cosmic Microwave Background. I will show how symmetry considerations lead us to three broad classes of theories to explain these perturbations: single-field inflation, multi-field inflation, and the conformal mechanism. We will discuss the symmetries in each case and derive their model-independent consequences. Finally, we will examine the possibility of violating the null energy condition with a well-behaved quantum field theory.
Hybrid quantization of the Gowdy model within loop quantum cosmology

Mercedes Martin-Benito Complutense University of Madrid
October 15, 2013

PIRSA:13100102
Cosmology
Loop quantum cosmology (LQC) proposes a quantization for homogeneous cosmologies which success in solving the classical singularity problem. Realistic scenarios call for the consideration of inhomogeneities. Focusing on the simplest inhomogenous cosmological model, the Gowdy model with three-torus spatial topology and linearly polarized gravitational waves, I'll describe an approach to treat inhomogeneities in the framework of loop quantum cosmology. This is a hybrid approach that combines LQC methods with Fock quantization. Furthermore, I'll discuss justified approximations that allow us to find approximate solutions to the (very complicated) Hamiltonian constraint of the model.
Einstein and the Fugu

Andrew Waldron University of California, Davis
October 10, 2013

PIRSA:13100101
Cosmology
A Nearly Gaussian Hubble-patch in a non-Gaussian Universe

Marilena LoVerde University of Washington
October 08, 2013

PIRSA:13100076
Cosmology
Local-type primordial non-Gaussianity couples statistics of the curvature perturbation \zeta on vastly different physical scales. Because of this coupling, statistics (i.e. the polyspectra) of \zeta in our Hubble volume may not be representative of those in the larger universe -- that is, they may be biased. The bias depends on the local background value of \zeta, which includes contributions from all modes with wavelength k ~< H_0 and is therefore enhanced if the entire post-inflationary patch is large compared with our Hubble volume. I will discuss the bias to locally-measured statistics for general local-type non-Gaussianity. I will discuss three examples in detail: (i) the usual fNL, gNL model, (ii) a strongly non-Gaussian model with \zeta ~ \zeta_G^p, and (iii) two-field non-Gaussian initial conditions. In each scenario one may generate statistics in a Hubble-size patch that are weakly Gaussian and consistent with observations despite the fact that the statistics in the larger, post-inflationary patch look very different. Finally, I will present a worked example of how the variation in local statistics arises in the curvaton scenario.

Title	Speaker(s)	Date	Talk Type	Info
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
Feedback-regulated star formation on galactic and cosmological scales	Claude-André Faucher-Giguère	2013-11-05	Scientific Series	View details
Aspects of Modified Gravity	Jeremy Sakstein	2013-10-31	Scientific Series	View details
Mapping Mass Across The Sky: CMB Lensing Measurements Past and Future	Blake Sherwin	2013-10-29	Scientific Series	View details
Conformal symmetry and cosmology	Austin Joyce	2013-10-22	Scientific Series	View details
Hybrid quantization of the Gowdy model within loop quantum cosmology	Mercedes Martin-Benito	2013-10-15	Scientific Series	View details
Einstein and the Fugu	Andrew Waldron	2013-10-10	Scientific Series	View details
A Nearly Gaussian Hubble-patch in a non-Gaussian Universe	Marilena LoVerde	2013-10-08	Scientific Series	View details

Cosmology and Gravitation

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