Cosmology and Gravitation

694 talks

S004

Collection TypeSeries

SubjectCosmology

Displaying 409 - 420 of 694

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

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

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

Enrico Pajer Utrecht University
March 19, 2013

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

Masahide Yamaguchi Tokyo Institute of Technology
March 12, 2013

PIRSA:13030096
Cosmology
Newton’s Method in Cosmology Today

Bill Harp Western University
February 26, 2013

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

Ewan Tarrant University of Nottingham
February 05, 2013

PIRSA:13020123
Cosmology
Cosmic Tides

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

PIRSA:13010114
Cosmology
Holographic description of cosmological singularity

Misha Smolkin Hebrew University of Jerusalem
January 22, 2013

PIRSA:13010111
Cosmology
Parameterizing dark sector perturbations

Jonathan Pearson Durham University
January 15, 2013

PIRSA:13010019
Cosmology
Fifth forces and new particles from dark energy

Amol Upadhye University of Wisconsin–Madison
January 08, 2013

PIRSA:13010023
Cosmology
A robust constraint on cosmic textures from the cosmic microwave background

Stephen Feeney
December 11, 2012

PIRSA:12120034
Cosmology
Nonlinear Extensions for the Inflationary Power Spectra

Shun-Pei Miao Utrecht University
December 11, 2012

PIRSA:12120014
Cosmology
CMB as a Probe of New Physics: The Story of Cosmic Birefringence
December 06, 2012

PIRSA:12120019
Cosmology

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

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

PIRSA:13040120
Cosmology
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
Cosmology
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
Cosmology
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
Cosmology
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
Cosmology
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
Cosmology
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
Cosmology
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.
Parameterizing dark sector perturbations

Jonathan Pearson Durham University
January 15, 2013

PIRSA:13010019
Cosmology
When recent observational evidence and the GR+FRW+CDM model are combined we obtain the result that the Universe is accelerating, where the acceleration is due to some not-yet-understood "dark sector". There has been a considerable number of theoretical models constructed in an attempt to provide an "understanding" of the dark sector: dark energy and modified gravity theories. The proliferation of modified gravity and dark energy models has brought to light the need to construct a "generic" way to parameterize the dark sector. We will discuss our new way of approaching this problem, looking at linearised perturbations. Our approach is inspired by that taken in particle physics, where the most general modifications to the standard model are written down for a given field content that is compatible with some assumed symmetry (which we take to be isotropy of the background spatial sections). Our emphasis is on constructing a theoretically motivated toolkit which can be used to extract meaningful information about the dark sector (such as its field content). We find, for example, that the observational impact of very broad classes of theories can be encoded by a very small (less than 5) number of parameters. It is these parameters which we hope to measure with observational data.
Fifth forces and new particles from dark energy

Amol Upadhye University of Wisconsin–Madison
January 08, 2013

PIRSA:13010023
Cosmology
Dark energy coupled to Standard Model fermions and gauge bosons gives rise to fifth forces and new particles, which are readily accessible to experiments from laboratory to cosmological scales. I will discuss chameleon and symmetron models, whose fifth forces are screened locally through large effective masses and symmetry-restoring phase transitions, respectively. Fifth force experiments such as the Eot-Wash torsion balance will test chameleons with small quantum corrections and gravitation-strength fifth forces, as well as symmetrons with coupling energies just beyond the Standard Model scale. A dark energy coupling to electromagnetism would imply that photons passing through a magnetic field will oscillate into particles of dark energy, a phenomenon studied by afterglow experiments such as CHASE. After constraining dark energy using laboratory experiments, I proceed to astrophysical probes. Particles of a photon-coupled dark energy could be produced in the Sun and detected in magnetic helioscopes such as CAST, while fifth forces may alter the dynamics of variable stars and the growth of large-scale structure.
A robust constraint on cosmic textures from the cosmic microwave background

Stephen Feeney
December 11, 2012

PIRSA:12120034
Cosmology
Fluctuations in the cosmic microwave background (CMB) contain information which has been pivotal in establishing the current cosmological model. These data can also be used to test well-motivated additions to this model, such as cosmic textures. Textures are a type of topological defect that can be produced during a cosmological phase transition in the early universe, and which leave characteristic hot and cold spots in the CMB. We apply Bayesian methods to carry out an optimal test of the texture hypothesis, using full-sky data from the Wilkinson Microwave Anisotropy Probe. We conclude that current data do not warrant augmenting the standard cosmological model with textures. We rule out at 95% confidence models that predict more than 6 detectable cosmic textures on the full sky.
Nonlinear Extensions for the Inflationary Power Spectra

Shun-Pei Miao Utrecht University
December 11, 2012

PIRSA:12120014
Cosmology
We expound several principles in an attempt to clarify the debate over infrared loop corrections to the primordial scalar and tensor power spectra from inflation. Among other things we note that existing proposals for nonlinear extensions of the scalar fluctuation field $\zeta$ introduce new ultraviolet divergences which no one understands how to renormalize. Loop corrections and higher correlators of these putative observables would also be enhanced by inverse powers of the slow roll parameter $\epsilon$. We propose an extension which might be better behaved.
CMB as a Probe of New Physics: The Story of Cosmic Birefringence
December 06, 2012

PIRSA:12120019
Cosmology
Cosmological birefringence is a postulated rotation of the linear polarization of photons that arises due to a Chern-Simons coupling of a new scalar field to electromagnetism. In particular, it appears as a generic feature of simple quintessence models for Dark Energy, and therefore, should it be detected, could provide insight into the microphysics of cosmic acceleration. Prior work has sought this rotation, assuming the rotation angle to be uniform across the sky, by looking for the parity-violating TB and EB correlations in the CMB temperature/polarization. However, if the scalar field that gives rise to cosmological birefringence has spatial fluctuations, then the rotation angle may vary across the sky. In this talk, I will present the results of the first CMB-based search for direction-dependent cosmological birefringence, using WMAP-7 data, and report the constraint on the rotation-angle power spectrum for all multipoles up to the resolution of the instrument. I will discuss the implications for a specific models for rotation, and show forecasts for Planck and future experiments. I will then conclude with a brief discussion of other exotic physical models, such as chiral gravity, and astrophysical scenarios, such as inhomogeneous reionization, that can be probed using the same analysis.

Title	Speaker(s)	Date	Talk Type	Info
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
Parameterizing dark sector perturbations	Jonathan Pearson	2013-01-15	Scientific Series	View details
Fifth forces and new particles from dark energy	Amol Upadhye	2013-01-08	Scientific Series	View details
A robust constraint on cosmic textures from the cosmic microwave background	Stephen Feeney	2012-12-11	Scientific Series	View details
Nonlinear Extensions for the Inflationary Power Spectra	Shun-Pei Miao	2012-12-11	Scientific Series	View details
CMB as a Probe of New Physics: The Story of Cosmic Birefringence		2012-12-06	Scientific Series	View details

Cosmology and Gravitation

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