Cosmology and Gravitation

688 talks

S004

Collection TypeSeries

SubjectCosmology

Displaying 385 - 396 of 688

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 System
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
Not so random walks in cosmology

Ravi Sheth University of Pennsylvania
September 24, 2013

PIRSA:13090063
Cosmology
ΛCDM Large Scale Triumphs and Small Scale Challenges

Joel Primack University of California, Santa Cruz
September 17, 2013

PIRSA:13090066
Cosmology
Peaks, excursion sets and the distribution of dark matter haloes

Vincent Desjacques Université de Genève
September 03, 2013

PIRSA:13090062
Cosmology
Effective Field Theory of Multi-Field Inflation a la Weinberg

Nima Khosravi Shahid Beheshti University
July 30, 2013

PIRSA:13070091
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
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 System
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.
Not so random walks in cosmology

Ravi Sheth University of Pennsylvania
September 24, 2013

PIRSA:13090063
Cosmology
I'll discuss a number of insights into the process of nonlinear structure formation which come from the study of random walks crossing a suitably chosen barrier. These derive from a number of new results about walks with correlated steps, and include a unified framework for the peaks and excursion set frameworks for estimating halo abundances, evolution and clustering, as well as nonlinear, nonlocal and stochastic halo bias, all of which matter for the next generation of large scale structure datasets.
ΛCDM Large Scale Triumphs and Small Scale Challenges

Joel Primack University of California, Santa Cruz
September 17, 2013

PIRSA:13090066
Cosmology
ΛCDM has become the standard cosmological model because its predictions agree so well with observations of the cosmic microwave background and the large-scale structure of the universe. However ΛCDM has faced challenges on smaller scales. Some of these challenges, including the “angular momentum catastrophe" and the absence of density cusps in the centers of small galaxies, may be overcome with improvements in simulation resolution and feedback. Recent simulations appear to form realistic galaxies in agreement with observed scaling relations. Although dark matter halos start small and grow by accretion, the existence of a star-forming band of halo masses naturally explains why the most massive galaxies have the oldest stars, a phenomenon known as galactic “downsizing." The discovery of many faint galaxies in the Local Group is consistent with the large number of subhalos in ΛCDM simulations. There is increasing evidence for such substructure in galaxy dark matter halos from gaps in cold stellar streams in the Milky Way and Andromeda and from gravitational lensing flux anomalies, with the prospect of rapidly increasing data on that from ALMA. The “too big to fail" (TBTF) problem is the latest apparent challenge to ΛCDM. It arose from analysis of the Aquarius and Via Lactea very-high-resolution ΛCDM simulations of Milky-Way-mass dark matter halos. Each simulated halo has ∼10 subhalos so massive and dense that they would appear to be too big to fail to form lots of stars. The TBTF problem is that none of the observed dwarf satellite galaxies of the Milky Way or Andromeda have stars moving as fast as would be expected in these densest subhalos. This may indicate the need for a more complex theory of dark matter – but several recent papers have shown that subhalos in pure dark matter simulations like Aquarius or Via Lactea are significantly modified when baryonic effects are included, so as to solve the TBTF problem. Higher resolution simulations are needed to verify this.
Peaks, excursion sets and the distribution of dark matter haloes

Vincent Desjacques Université de Genève
September 03, 2013

PIRSA:13090062
Cosmology
I will review recent developments in our theoretical understanding of the abundance and clustering of dark matter haloes. In the first part of this talk, I will discuss a toy model based on the statistics of peaks of Gaussian random field (Bardeen et al 1986) and show how the clustering properties of such a point set can be easily derived from a generalised local bias expansion. In the second part, I will explain how this peak formalism relates to the excursion set approach and present parameter-free predictions for the mass function and bias of dark matter halos.
Effective Field Theory of Multi-Field Inflation a la Weinberg

Nima Khosravi Shahid Beheshti University
July 30, 2013

PIRSA:13070091
Cosmology
We
employ the effective field theory approach for multi-field inflation which is a
generalization of Weinberg's work. In this method the first correction terms in
addition to standard terms in the Lagrangian have been considered. These terms
contain up to the fourth derivative of the fields including the scalar field
and the metric. The results show the possible shapes of the interaction terms
resulting eventually in non-Gaussianity in a general formalism. In addition
generally the speed of sound is different but almost unity. Since in this
method the adiabatic mode is not discriminated initially so we define the
adiabatic as well as entropy modes for a specific two-field model. It has been
shown that the non-Gaussianity of the adiabatic mode and the entropy mode are
correlated in shape and amplitude. It is shown that even for speed close to
unity large non-Gaussianities are possible in multi-field case. The amount of
the non-Gaussianity depends on the curvature of the classical path in the
phase-space in the Hubble unit such that it is large for the large curvature.
In addition it is emphasized that the time derivative of adiabatic and entropy
perturbations do not transform due to the shift symmetry as well as the
original perturbations. Though two specific combinations of them are invariant
under such a symmetry and these combinations should be employed to construct an
effective field theory of multi-field inflation.

Title	Speaker(s)	Date	Talk Type	Info
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
Not so random walks in cosmology	Ravi Sheth	2013-09-24	Scientific Series	View details
ΛCDM Large Scale Triumphs and Small Scale Challenges	Joel Primack	2013-09-17	Scientific Series	View details
Peaks, excursion sets and the distribution of dark matter haloes	Vincent Desjacques	2013-09-03	Scientific Series	View details
Effective Field Theory of Multi-Field Inflation a la Weinberg	Nima Khosravi	2013-07-30	Scientific Series	View details

Cosmology and Gravitation

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