Cosmology and Gravitation

694 talks

S004

Collection TypeSeries

SubjectCosmology

Displaying 373 - 384 of 694

Cosmology Results from the Pan-STARRs Supernova Survey

Danial Scolnic Johns Hopkins University
March 04, 2014

PIRSA:14030095
Cosmology
Probing the Small Scale Structure of Dark Matter with Indirect Detection

Sheldon Campbell Ohio State University
February 25, 2014

PIRSA:14020097
Cosmology
Evolution of cosmological black holes: exact solutions, accretion and scalar fields

Daniel Guariento Conestoga College
February 18, 2014

PIRSA:14020150
Cosmology
Our Lopsided Universe

Marina Cortes Institute for Astrophysics and Space Sciences
February 11, 2014

PIRSA:14020139
Cosmology
Cosmological constraints on complex scalar-field dark matter

Tanja Rindler-Daller University of Michigan–Ann Arbor
February 04, 2014

PIRSA:14020096
Cosmology
New light on 21cm intensity fluctuations from the dark ages
January 28, 2014

PIRSA:14010097
Cosmology
Cosmic Variance from Superhorizon Mode Coupling

Elliot Nelson
January 23, 2014

PIRSA:14010107
Cosmology
The McV black hole and the scalar theories that support it

Michele Fontanini
January 21, 2014

PIRSA:14010082
Cosmology
Simulating the Universe(s)

Matthew Johnson York University
January 14, 2014

PIRSA:14010101
Cosmology
Scale-free primordial cosmology

Anna Ijjas Max Planck Institute for Gravitational Physics - Albert Einstein Institute (AEI)
December 19, 2013

PIRSA:13120063
Cosmology
holographic path to the turbulent side of gravity
- Adam Brown Stanford University
- Stephen Green University of Nottingham
December 12, 2013

PIRSA:13120066
Cosmology
Consistency of Massive Gravity

Lavinia Heisenberg ETH Zurich
December 10, 2013

PIRSA:13120061
Cosmology

Cosmology Results from the Pan-STARRs Supernova Survey

Danial Scolnic Johns Hopkins University
March 04, 2014

PIRSA:14030095
Cosmology
The Pan-STARRs supernova survey has discovered one of the largest samples of Type Ia supernovae. Measurements of the distances to these supernovae allow us to probe some of the most fundamental questions about the properties of the universe like what is dark energy. When combining measurements from various astrophysical probes, we find hints of interesting tension with the Lambda-CDM model. I discuss the various combinations of astrophysical probes and the source of this tension. It is possible that this tension is due to systematic uncertainties in the various measurements, and I show how we analyze these uncertainties in the Pan-STARRs sample.
Probing the Small Scale Structure of Dark Matter with Indirect Detection

Sheldon Campbell Ohio State University
February 25, 2014

PIRSA:14020097
Cosmology
Direct observation of the small scale structure of matter in the Universe provides potentially important information about a wealth of physics, from complex galaxy evolution processes to fundamental particle properties of dark matter. Detecting this fine structure in dark matter, though, is notoriously difficult. Dark matter indirect detection--through observation of radiation products of particle annihilation--may be the most direct method for observing small scale structure. However, in an observed signal, the amount of dark matter clustering is degenerate with the annihilation cross section. This talk outlines ways this degeneracy may be broken with indirect detection alone. Scenarios are discussed where either abundant substructure leads to discovery of annihilation radiation (revealing properties of the substructure), or a discovery strongly constrains the presence of significant dark matter halo substructure.
Evolution of cosmological black holes: exact solutions, accretion and scalar fields

Daniel Guariento Conestoga College
February 18, 2014

PIRSA:14020150
Cosmology
Systems which contemplate the gravitational interaction between compact objects and the matter content in a cosmological environment constitute an important problem which has been studied since the early days of General Relativity. The generalized McVittie black hole is a simple exact solution to this problem, which provides us with insight on some of its known physical aspects, as well as hints to new mechanisms which arise from a formal treatment. We review some properties of this solution and its matter source, which can be interpreted as a classical fluid but is also an exact solution to a nontrivial scalar field theory.
Our Lopsided Universe

Marina Cortes Institute for Astrophysics and Space Sciences
February 11, 2014

PIRSA:14020139
Cosmology
After a short introduction to open inflation and the observed large-scale cosmic microwave anomalies, which have been confirmed by the Planck satellite, I'll argue that the anomalies are naturally explained in the context of a marginally-open, negatively curved universe. I'll look in particular at the dipole power asymmetry, and motivate that this asymmetry can happen if our universe has bubble nucleated in a phase transition during a period of early inflation, and, as a result, has open geometry. Open inflation models, which are motivated by the string landscape and can excite `super-curvature' perturbation modes, can explain the presence of a very-large-scale perturbation, like the one we observe, which leads to a dipole modulation of the power spectrum. I'll provide a specific implementation of the scenario which is compatible with all existing constraints.
Cosmological constraints on complex scalar-field dark matter

Tanja Rindler-Daller University of Michigan–Ann Arbor
February 04, 2014

PIRSA:14020096
Cosmology
The nature of dark matter is a fundamental problem in cosmology and particle physics. Many particle candidates have been devised over the course of the last decades, and are still at stake to be soon discovered or rejected. However, astronomical observations, in conjunction with the phenomenological efforts in astrophysical modeling, as well as in particle theories to explain them, have helped to pin down several key properties which any successful candidate has to have. In this talk, I will explore the possibility that dark matter is described by a complex scalar field (SFDM), while the other cosmic components are treated in the usual way, assuming a cosmological constant for the dark energy. We will see that the background evolution of a Universe with SFDM and a cosmological constant (LSFDM) complies with the concordance LCDM model, if the model parameters of the SFDM Lagrangian, mass and repulsive 2-particle self-interaction coupling strength, are properly constrained by observations of the cosmic microwave background and Big Bang nucleosynthesis (BBN). However, not only does LSFDM lead to non-standard expansion histories prior to BBN, it also exemplifies differences at small scales, which could help to resolve the discrepancies found between LCDM and certain galaxy observations. I will highlight the differences between complex SFDM and dark matter described by real fields, as for instance axion-like particles. If time permits, I will also talk about possible implementations of SFDM in the very early Universe, in the wake of its inflationary phase.
New light on 21cm intensity fluctuations from the dark ages
January 28, 2014

PIRSA:14010097
Cosmology
Fluctuations of the 21 cm brightness temperature before the formation of the first stars hold the promise of becoming a high-precision cosmological probe in the future. The growth of over densities is very well described by perturbation theory at that epoch and the signal can in principle be predicted to arbitrary accuracy for given cosmological parameters. Recently, Tseliakhovich and Hirata pointed out a previously neglected and important physical effect, due to the fact that baryons and cold dark matter (CDM) have supersonic relative velocities after recombination. This relative velocity suppresses the growth of matter fluctuations on scales k∼10−10^3 Mpc^−1. In addition, the amplitude of the small-scale power spectrum is modulated on the large scales over which the relative velocity varies, corresponding to k∼0.005−1 Mpc^−1. In this talk, I will describe the effect of the relative velocity on 21 cm brightness temperature fluctuations from redshifts z≥30. I will show that the 21 cm power spectrum is affected on most scales. On small scales, the signal is typically suppressed several tens of percent, except for extremely small scales (k≳2000 Mpc−1) for which the fluctuations are boosted by resonant excitation of acoustic waves. On large scales, 21 cm fluctuations are enhanced due to the non-linear dependence of the brightness temperature on the underlying gas density and temperature. The enhancement of the 21 cm power spectrum is of a few percent at k∼0.1 Mpc−1 and up to tens of percent at k≲0.005 Mpc−1, for standard ΛCDM cosmology. In principle this effect allows to probe the small-scale matter power spectrum not only through a measurement of small angular scales but also through its effect on large angular scales.
Cosmic Variance from Superhorizon Mode Coupling

Elliot Nelson
January 23, 2014

PIRSA:14010107
Cosmology
We observe a finite subvolume of the universe, so CMB and large scale structure data may give us either a representative or a biased sample of statistics in the larger universe. Mode coupling (non-Gaussianity) in the primordial perturbations can introduce a bias of parameters measured in any subvolume due to coupling to superhorizon background modes longer than the size of the subvolume. This leads to a "cosmic variance" of statistics on smaller scales, as the long-wavelength background modes vary around the global mean. We study this bias for local non-Gaussianity and quantify how observed statistics such as the power spectrum of the primordial perturbations, spectral index (scale-dependence in the power spectrum), amplitude of non-Gaussianity, dark matter halo power spectrum, and primordial tensor modes, can differ from the same quantities averaged throughout a volume much larger than the observable universe. More general kinds of mode coupling can change the relative sensitivity to different background modes. Finally, we consider what observations can tell us about the possibility of biasing from superhorizon modes."
The McV black hole and the scalar theories that support it

Michele Fontanini
January 21, 2014

PIRSA:14010082
Cosmology
Systems in which the local gravitational attraction is coupled to the expansion of the Universe have been studied since the early stages of General Relativity as the pioneering works of McVittie show. In this talk I start reviewing the McVittie black hole solution and its variable mass generalization from a classical fluid approach to understand its properties. I then move to a field theoretical analysis to investigate the scalar theories that support such black holes.
Simulating the Universe(s)

Matthew Johnson York University
January 14, 2014

PIRSA:14010101
Cosmology
The theory of eternal inflation in an inflaton potential with multiple vacua predicts that our universe is one of many bubble universes nucleating and growing inside an ever-expanding false vacuum. The collision of our bubble with another could provide an important observational signature to test this scenario. In this talk I will describe an algorithm for accurately computing the cosmological observables arising from bubble collisions directly from the Lagrangian of a single scalar field. This represents the first fully-relativistic set of predictions from an ensemble of scalar field models giving rise to eternal inflation, and I will describe on-going phenomenological studies and observational searches.
Scale-free primordial cosmology

Anna Ijjas Max Planck Institute for Gravitational Physics - Albert Einstein Institute (AEI)
December 19, 2013

PIRSA:13120063
Cosmology
The large-scale structure of the universe suggests that the physics underlying its early evolution is scale-free. In this talk, using a hydrodynamic approach, I will discuss how the scale-free principle restores predictive power and makes it possible to evaluate inflationary models and to compare them with alternative cosmologies.
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."
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.

Title	Speaker(s)	Date	Talk Type	Info
Cosmology Results from the Pan-STARRs Supernova Survey	Danial Scolnic	2014-03-04	Scientific Series	View details
Probing the Small Scale Structure of Dark Matter with Indirect Detection	Sheldon Campbell	2014-02-25	Scientific Series	View details
Evolution of cosmological black holes: exact solutions, accretion and scalar fields	Daniel Guariento	2014-02-18	Scientific Series	View details
Our Lopsided Universe	Marina Cortes	2014-02-11	Scientific Series	View details
Cosmological constraints on complex scalar-field dark matter	Tanja Rindler-Daller	2014-02-04	Scientific Series	View details
New light on 21cm intensity fluctuations from the dark ages		2014-01-28	Scientific Series	View details
Cosmic Variance from Superhorizon Mode Coupling	Elliot Nelson	2014-01-23	Scientific Series	View details
The McV black hole and the scalar theories that support it	Michele Fontanini	2014-01-21	Scientific Series	View details
Simulating the Universe(s)	Matthew Johnson	2014-01-14	Scientific Series	View details
Scale-free primordial cosmology	Anna Ijjas	2013-12-19	Scientific Series	View details
holographic path to the turbulent side of gravity	Adam Brown, Stephen Green	2013-12-12	Scientific Series	View details
Consistency of Massive Gravity	Lavinia Heisenberg	2013-12-10	Scientific Series	View details

Cosmology and Gravitation

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