Cosmology and Gravitation

687 talks

S004

Collection TypeSeries

SubjectAstrophysics

Source RepositoryPIRSA

Displaying 397 - 408 of 687

Axiverse Cosmology and the Energy Scale of Inflation

David Marsh King's College London
May 07, 2013

PIRSA:13050054
Astrophysics
Transporting non-Gaussianity from sub- to super- horizon scales

David Mulryne Queen Mary University of London
April 30, 2013

PIRSA:13040128
Astrophysics
On memory in exponentially expanding spaces

Douglas Stanford Stanford University
April 23, 2013

PIRSA:13040127
Astrophysics
Results and highlights from Planck

Kendrick Smith Perimeter Institute for Theoretical Physics
April 16, 2013

PIRSA:13040123
Astrophysics
Large Scale Bayesian Inference in Cosmology

Jens Jasche Institut d'Astrophysique de Paris
April 11, 2013

PIRSA:13040119
Astrophysics
The Death Throes of Massive Stars: Supernovae, Black Holes, and Neutrinos

Evan O'Connor California Institute of Technology
April 09, 2013

PIRSA:13040120
Astrophysics
The Effective Field Theory of Large Scale Structures

Enrico Pajer Utrecht University
March 19, 2013

PIRSA:13030110
Astrophysics
Effective field theory approach to quasi-single field inflation

Masahide Yamaguchi Tokyo Institute of Technology
March 12, 2013

PIRSA:13030096
Astrophysics
Newton’s Method in Cosmology Today

Bill Harp Western University
February 26, 2013

PIRSA:13020151
Astrophysics
Multifield Reheating and the Fate of the Primordial Observables

Ewan Tarrant University of Nottingham
February 05, 2013

PIRSA:13020123
Astrophysics
Cosmic Tides

Ue-Li Pen Canadian Institute for Theoretical Astrophysics (CITA)
January 29, 2013

PIRSA:13010114
Astrophysics
Holographic description of cosmological singularity

Misha Smolkin Hebrew University of Jerusalem
January 22, 2013

PIRSA:13010111
Astrophysics

Axiverse Cosmology and the Energy Scale of Inflation

David Marsh King's College London
May 07, 2013

PIRSA:13050054
Astrophysics
Ultra-light axions (m_a<10^{-18} eV), motivated by string theory, can be a powerful probe of the energy scale of inflation if they exist as a sub-dominant component of the Dark Matter. In contrast to heavier axions the isocurvature modes in the ultra-light axions can coexist with observable gravitational waves. Here it is shown that existing (2005) large scale structure constraints severely limit the parameter space for axion mass, density fraction and isocurvature amplitude. It is also shown that radically different CMB observables for the ultra-light axion isocurvature mode additionally reduce this space. The results of a new, accurate and efficient method to calculate this isocurvature power spectrum are presented, and can be used to constrain ultra-light axions and inflation.
I will also present preliminary results of constraints to this model using up-to-date cosmological observations, which verify the above picture. The parameter space is interesting to explore due to a strongly mass dependent covariance matrix, motivating comparisons between Metropolis-Hastings and nested sampling. Finally I discuss fine-tuning and naturalness in these models.
Transporting non-Gaussianity from sub- to super- horizon scales

David Mulryne Queen Mary University of London
April 30, 2013

PIRSA:13040128
Astrophysics
The non-Gaussian statistics of the primordial density perturbation have become a key test of the inflationary scenario of the very early universe. Currently many techniques are used to calculate the non-Gaussian signatures of a given model of inflation. In particular, simple super-horizon techniques such as the deltaN formalism are often used for models with more than one field, while more technical field theory techniques, referred to as the In-In formalism, are typically used for models where the quantum sub-horizon evolution is important. Recently we have been developing an alternative point of view, called the transport approach. This framework highlights the connections between these other techniques and unifies them. Moreover, since it reduces the problem of calculating the statistics to that of solving a set of coupled ODEs, numerical implementations of the system are extremely simple.
On memory in exponentially expanding spaces

Douglas Stanford Stanford University
April 23, 2013

PIRSA:13040127
Astrophysics
I will present recent work, done in collaboration with Daniel Roberts, on the global memory of initial conditions that is sometimes, but not always, retained by fluctuating fields on de Sitter space, Euclidean anti de Sitter space, and regular infinite trees. I will discuss applications to the structure of configuration space in de Sitter space and eternal inflation.
Results and highlights from Planck

Kendrick Smith Perimeter Institute for Theoretical Physics
April 16, 2013

PIRSA:13040123
Astrophysics
Cosmological results from Planck, a third-generation satellite mission to measure the cosmic microwave background, have just been announced. These results improve constraints on essentially all cosmological parameters, and have implications for several preexisting sources of tension with the standard cosmological model, while also raising new puzzles. I will discuss these results and their significance, as well as the next steps forward.
Large Scale Bayesian Inference in Cosmology

Jens Jasche Institut d'Astrophysique de Paris
April 11, 2013

PIRSA:13040119
Astrophysics
Already the last decade has witnessed unprecedented progress in the collection of cosmological data. Presently proposed and designed future cosmological probes and surveys permit us to anticipate the upcoming avalanche of cosmological information during the next decades.
The increase of valuable observations needs to be accompanied with the development of efficient and accurate information processing technology in order to analyse and interpret this data. In particular, cosmography projects, aiming at studying the origin and inhomogeneous evolution of
the Universe, involve high dimensional inference methods. For example, 3d cosmological density and velocity field inference requires to explore on the order of 10^7 or more parameters. Consequently, such projects critically rely on state-of-the-art information processing techniques
and, nevertheless, are often on the verge of numerical feasibility with present day computational resources. For this reason, in this talk I will address the problem of high dimensional Bayesian inference from cosmological data sets, subject to a variety of statistical and systematic uncertainties. In particular, I will focus on the discussion of selected Markov Chain Monte Carlo techniques, permitting to efficiently solve inference problems with on the order of 10^7 parameters. Furthermore, these methods will be exemplified in various cosmological applications, raging from 3d non-linear density and photometric redshift inference to 4d physical state inference. These techniques permit us to exploit cosmologically relevant information from
observations to unprecedented detail and hence will significantly contribute to the era of precision cosmology.
The Death Throes of Massive Stars: Supernovae, Black Holes, and Neutrinos

Evan O'Connor California Institute of Technology
April 09, 2013

PIRSA:13040120
Astrophysics
The endgame of massive star evolution is the gravitational-induced collapse of the central inert iron core. The collapse of the core continues until the matter reaches nuclear densities where the strong force between nucleons becomes dominant and provides sufficient pressure to stabilize the newly formed protoneutron star. What ensues is a complex multi-physics problem involving strong gravity, multidimensional hydrodynamic instabilities, magnetic fields, multispecies neutrino radiation, and supranuclear density physics to name a few.

We expect that most massive stars end this final stage of stellar evolution with a successful core-collapse supernova explosion. However, we also know that some of these core collapse events must fail and form stellar mass black holes.In his talk I will touch on two of the most important questions in core-collapse supernovae theory. I will briefly talk about what conditions are favourable for failed core-collapse supernovae (i.e. black hole formation). Conversely, I will discuss recent results from full three-dimensional, general-relativistic simulations of core-collapse and the implications for our understanding of the core-collapse supernova mechanism. If time permits, I'll discuss how neutrinos from the next galactic core-collapse supernova can help constrain properties of massive stars.
The Effective Field Theory of Large Scale Structures

Enrico Pajer Utrecht University
March 19, 2013

PIRSA:13030110
Astrophysics
An analytical understanding of large-scale matter inhomogeneities is an important cornerstone of our cosmological model and helps us interpreting current and future data. The standard approach, namely Eulerian perturbation theory, is unsatisfactory for at least three reasons: there is no clear expansion parameter since the density contrast is not small everywhere; it does not consistently account for deviations at large scales from a perfect pressureless fluid induced by short-scale non-linearities; for generic initial conditions, loop corrections are UV divergent, making predictions cutoff dependent and hence unphysical. I will present the systematic construction of an Effective Field Theory of Large Scale Structures and show that it successfully addresses all of the above issues. The idea is to smooth the density and velocity fields on a scale larger than the non-linear scale. The resulting smoothed fields are then small everywhere and provide a well-defined small parameter for perturbation theory. Smoothing amounts to integrating out the short scales, whose non-linear dynamics is hard to describe analytically. Their effects on the large scales are then determined by the symmetries of the problems. They introduce additional terms in the fluid equations such as an effective pressure, dissipation and stochastic noise. These terms have exactly the right scale dependence to cancel all divergences at one loop, and this should hold at all loops.
I will present a clean example of the renormalization of the theory in an Einstein de Sitter universe with self-similar initial conditions and discuss the relative importance of loop and effective corrections.
Effective field theory approach to quasi-single field inflation

Masahide Yamaguchi Tokyo Institute of Technology
March 12, 2013

PIRSA:13030096
Astrophysics
We apply the effective field theory approach to quasi-single field inflation, which contains an additional scalar field with Hubble scale mass other than inflaton. Based on the time-dependent spatial diffeomorphism, which is not broken by the time-dependent background evolution, the most generic action of quasi-single field inflation is constructed up to third order fluctuations. Using the obtained action, the effects of the additional massive scalar field on the primordial curvature perturbations are discussed. In particular, we calculate the power spectrum and discuss the momentum-dependence of three point functions in the squeezed limit for general settings of quasi-single field inflation. Our framework can be also applied to inflation models with heavy particles. We make a qualitative discussion on the effects of heavy particles during inflation and that of sharp turning trajectory in our framework.
Newton’s Method in Cosmology Today

Bill Harp Western University
February 26, 2013

PIRSA:13020151
Astrophysics
Newton’s inferences from phenomena realize an ideal of empirical success that’s richer than prediction. To realize Newton’s richer conception of empirical success a theory needs to do more than to accurately predict the phenomena it purports to explain: in addition it needs to have the phenomena accurately measure parameters of the theory. Newton’s method aims to turn theoretical questions into ones which can be empirically answered by measurements from phenomena. Propositions inferred from phenomena are provisionally accepted as guides to further research. Newton’s ideal of empirical success as agreeing measurements from diverse phenomena is appealed to in support of the radical inference to dark energy in cosmology today. Robert Kirshner (two of his PhDs share one half of 2011’s Nobel Prize in physics) gave an account of the role of cosmic microwave background measurements, to back up the supernova measurements and measurements from galaxy clustering in supporting the transition of dark energy from a wild hypothesis into an accepted background assumption that guides further research in cosmology today. This illustrates a feature of agreeing measurements from diverse phenomena that is especially important for turning data into evidence. To the extent that the sources of systematic error of the different measurements can be regarded as independent, their agreement contributes additional support for counting them as accurate rather than as mere artifacts of systematic error.
Multifield Reheating and the Fate of the Primordial Observables

Ewan Tarrant University of Nottingham
February 05, 2013

PIRSA:13020123
Astrophysics
The presence of additional light fields during inflation can source isocurvature fluctuations, which can cause the curvature perturbation $\zeta$, and its statistics to evolve on superhorizon scales. I will demonstrate that if these fluctuations have not completely decayed before the onset of perturbative reheating, then primordial observables such as the level of non--Gaussianity can develop substantial reheating dependant corrections. I will argue that for inflationary models where an adiabatic condition is not reached before the relevant fields begin to decay, we must be careful in our interpretation of any observational constraints that place bounds on the statistics of $\zeta$.
Cosmic Tides

Ue-Li Pen Canadian Institute for Theoretical Astrophysics (CITA)
January 29, 2013

PIRSA:13010114
Astrophysics
We apply CMB lensing techniques to large scale structure and solve for the 3-D cosmic tidal field. We use small scale filamentary structures to solve for the large scale tidal shear and gravitational potential. By comparing this to the redshift space density field, one can measure the gravitational growth factor on large scales without cosmic variance. This potentially enables accurate measurements of neutrino masses and reconstruction of radial modes lost in 21 cm intensity mapping, which are essential for CMB and other cross correlations. We relate the tidal fields to the squeezed limit bispectrum, and present initial results from simulations and data from the SDSS.
Holographic description of cosmological singularity

Misha Smolkin Hebrew University of Jerusalem
January 22, 2013

PIRSA:13010111
Astrophysics
In my talk I will discuss our recent paper hep-th/1211.1322 where we construct a 3D conformal field theory dual to asymptotically AdS cosmology in four dimensions. Due to the scale invariance this dual theory allows an infinite family of instantons each of which breaks the conformal group O(3,2) down to O(3,1). These instantons are dual to bulk instantons responsible for nucleating an O(3,1) invariant cosmological bubble. Presumably they indicate an infinite instability rate, however we are able to sum over all of them completely. The resulting theory is manifestly stable, unitary and finite.

Title	Speaker(s)	Date	Talk Type	Info
Axiverse Cosmology and the Energy Scale of Inflation	David Marsh	2013-05-07	Scientific Series	View details
Transporting non-Gaussianity from sub- to super- horizon scales	David Mulryne	2013-04-30	Scientific Series	View details
On memory in exponentially expanding spaces	Douglas Stanford	2013-04-23	Scientific Series	View details
Results and highlights from Planck	Kendrick Smith	2013-04-16	Scientific Series	View details
Large Scale Bayesian Inference in Cosmology	Jens Jasche	2013-04-11	Scientific Series	View details
The Death Throes of Massive Stars: Supernovae, Black Holes, and Neutrinos	Evan O'Connor	2013-04-09	Scientific Series	View details
The Effective Field Theory of Large Scale Structures	Enrico Pajer	2013-03-19	Scientific Series	View details
Effective field theory approach to quasi-single field inflation	Masahide Yamaguchi	2013-03-12	Scientific Series	View details
Newton’s Method in Cosmology Today	Bill Harp	2013-02-26	Scientific Series	View details
Multifield Reheating and the Fate of the Primordial Observables	Ewan Tarrant	2013-02-05	Scientific Series	View details
Cosmic Tides	Ue-Li Pen	2013-01-29	Scientific Series	View details
Holographic description of cosmological singularity	Misha Smolkin	2013-01-22	Scientific Series	View details

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Cosmology and Gravitation

Format results

Axiverse Cosmology and the Energy Scale of Inflation

Transporting non-Gaussianity from sub- to super- horizon scales

On memory in exponentially expanding spaces

Results and highlights from Planck

Large Scale Bayesian Inference in Cosmology

The Death Throes of Massive Stars: Supernovae, Black Holes, and Neutrinos

The Effective Field Theory of Large Scale Structures

Effective field theory approach to quasi-single field inflation

Newton’s Method in Cosmology Today

Multifield Reheating and the Fate of the Primordial Observables

Cosmic Tides

Holographic description of cosmological singularity

Axiverse Cosmology and the Energy Scale of Inflation

Transporting non-Gaussianity from sub- to super- horizon scales

On memory in exponentially expanding spaces

Results and highlights from Planck

Large Scale Bayesian Inference in Cosmology

The Death Throes of Massive Stars: Supernovae, Black Holes, and Neutrinos

The Effective Field Theory of Large Scale Structures

Effective field theory approach to quasi-single field inflation

Newton’s Method in Cosmology Today

Multifield Reheating and the Fate of the Primordial Observables

Cosmic Tides

Holographic description of cosmological singularity