Event | Date | Summary |
Learning about Aspects of Clusters and Cosmology from Weak and Strong Gravitational Lensing Approaches – Mandeep Gill | Tue. April 12th, 2011 11:30 am-12:30 pm |
I will cover several aspects of current astrophysics that can be probed by various regimes of lensing in simulations and data –from galaxy cluster substructure to what we can learn about cosmology from cluster weak lensing ensembles. Further, a new approach to extracting information from strongly lensed arc images that I have been involved with in recent times, and which is model-independent and has the potential to revolutionize approaches to strong lensing analyses and is very complementary to weak lensing analyses will be introduced. I will further briefly discuss initial lensing results from already-taken data of 6 clusters from the Large Binocular Telescope in Arizona, |
Thick-wall tunneling in a piecewise linear and quadratic potential – Pascal Vaudrevange | Tue. April 12th, 2011 11:30 am-12:30 pm |
After reviewing the basics of Coleman deLuccia tunneling, especially in the thin-wall limit, I discuss an (almost) exact tunneling solution in a piecewise linear and quadratic potential. A comparison with the exact solution for a piecewise linear potential demonstrates the dependence of the tunneling rate on the exact shape of the potential. Finally, I will mention applications when determining initial conditions for inflation in the landscape. Based on arXiv:1102.4742 [hep-th]. |
Gravitational wave astronomy in the next decade – Xavier Siemens | Tue. April 5th, 2011 11:30 am-12:30 pm |
In the next decade two types of gravitational wave experiments are expected to result in the direct detection of gravitational waves: Advanced ground-based interferometric detectors and pulsar timing experiments. In my talk I will describe both types of experiments and their sensitivities to various types of gravitational wave sources. I will also discuss some of the impacts of these experiments on astronomy and cosmology. Continue reading… Gravitational wave astronomy in the next decade – Xavier Siemens |
Testing Dark Energy with Massive Galaxy Clusters – Michael Mortonson | Tue. March 29th, 2011 11:30 am-12:30 pm |
Existing observations of the cosmic expansion history place strong restrictions on the rate of large scale structure growth predicted by various dark energy models. In the simplest Lambda CDM scenario, current observations enable percent-level predictions of growth, which can be interpreted in terms of the expected abundance of massive galaxy clusters at high redshift. I will show that these predictions from current data set a firm upper limit on the cluster abundance in the more general class of quintessence models where dark energy is a canonical, minimally-coupled scalar field. While the most massive clusters known today appear to lie just below this limit, Continue reading… Testing Dark Energy with Massive Galaxy Clusters – Michael Mortonson |
New observational power from halo bias – Sarah Shandera | Tue. March 22nd, 2011 11:30 am-12:30 pm |
Non-Gaussianity of the local type will be particularly well constrained by large scale structure through measurements of the power spectra of collapsed objects. Motivated by properties of early universe scenarios that produce observationally large local non-Gaussianity, we suggest a generalized local ansatz and perform N-body simulations to determine the signatures in the bias of dark matter halos. The ansatz introduces two bispectral indices that characterize how the local non-Gaussianity changes with scale and these generate two new signals in the bias. While analytic predictions agree qualitatively with the simulations, we find numerically a stronger observational signal than expected, which suggests that a better analytic understanding is needed to fully explain the consequences of primordial non-Gaussianity. Continue reading… New observational power from halo bias – Sarah Shandera |
Constraining the cosmic growth history with large scale structure – Rachel Bean | Tue. March 15th, 2011 11:30 am-12:30 pm |
We consider how upcoming, prospective large scale structure surveys, measuring galaxy weak lensing, position and peculiar velocity correlations, in tandem with the CMB temperature anisotropies, will constrain dark energy when both the expansion history and growth of structure can be modified, as might arise if cosmic acceleration is due to modifications to GR. We consider an equation of state figure of merit parameter, and analogous figure of merit parameters for modified gravity, to quantify the relative constraints from CMB, galaxy position, lensing, and peculiar velocity observations and their cross correlations, independently and in tandem. Continue reading… Constraining the cosmic growth history with large scale structure – Rachel Bean |
What to do with 350,000 astronomers – Chris Lintott | Fri. February 18th, 2011 11:30 am-12:30 pm |
Since its launch in 2007, the Galaxy Zoo project has involved hundreds of thousands of volunteers in the morphological classification of galaxies. Project PI Chris Lintott will review the results – which include a new understanding of the importance of red spirals – and their implications for our understanding of galaxy formation. The project has now expanded to include tasks ranging from discovering planets through to lunar classification, and the talk will also discuss the potential of this ‘citizen science’ method to help scientists cope with massive modern data sets. Continue reading… What to do with 350,000 astronomers – Chris Lintott |
Astrophysics with Gravitational-Wave Detectors – Vuk Mandic | Tue. February 8th, 2011 11:30 am-12:30 pm |
Gravitational waves are predicted by the general theory of relativity to be produced by accelerating mass systems with quadrupole moment. The amplitude of gravitational waves is expected to be very small, so the best chance of their direct detection lies with some of the most energetic events in the universe, such as mergers of two neutron stars or black holes, Supernova explosions, or the Big-Bang itself. I will review the status of current gravitational-wave detectors, such as the Laser Interferometer Gravitational-wave Observatory (LIGO), as well as some of the most recent results obtained using LIGO data. I will also discuss plans and expectations for the future generations of gravitational-wave detectors. Continue reading… Astrophysics with Gravitational-Wave Detectors – Vuk Mandic |
New and Old Massive Gravity – Claudia de Rham | Tue. February 1st, 2011 11:30 am-12:30 pm |
TBA Continue reading… New and Old Massive Gravity – Claudia de Rham |
A new method for cosmological parameter estimation from Supernovae Type Ia data – Marisa March | Tue. January 18th, 2011 11:30 am-12:30 pm |
We present a new methodology to extract constraints on cosmological parameters from SNIa data obtained with the SALT lightcurve fitter. The power of our Bayesian method lies in its full exploitation of relevant prior information, which is ignored by the usual chisquare approach. Using realistic simulated data sets we demonstrate that our method outperforms the usual chisquare approach 2/3 of the times. A further benefit of our methodology is its ability to produce a posterior probability distribution for the intrinsic dispersion of SNe. This feature can also be used to detect hidden systematics in the data. |
K-essence Interactions with Neutrinos: Flavor Oscillations without Mass – Christopher Gauthier | Tue. December 7th, 2010 11:30 am-12:30 pm |
In this talk we discuss a novel means of coupling neutrinos to a Lorentz violating background k-essence field. K-essence is a model of dark energy, which uses a non-canonical scalar field to drive the late time accelerated expansion of the universe. We propose that neutrinos couple to the k-essence induced metric rather than the space-time metric. The immediate effect that this has will be to modify the energy-momentum relation of the neutrino. This implies that the neutrino velocity will in general be different from the speed of light, even if the neutrino is massless. Later we will see that k-essence can also induce neutrino oscillations even without a neutrino mass term. |
Light from Cosmic Strings – Tanmay Vachaspati | Tue. November 16th, 2010 11:30 am-12:30 pm |
TBA Continue reading… Light from Cosmic Strings – Tanmay Vachaspati |
Testing the No-Hair Theorem with Astrophysical Black Holes – Dmitrios Psaltis | Tue. November 2nd, 2010 11:30 am-12:30 pm |
The Kerr spacetime of spinning black holes is one of the most intriguing predictions of Einstein’s theory of general relativity. The special role this spacetime plays in the theory of gravity is encapsulated in the no-hair theorem, which states that the Kerr metric is the only realistic black-hole solution of the vacuum field equations. Recent and anticipated advances in the observations of black holes throughout the electromagnetic spectrum have secured our understanding of their basic properties while opening up new opportunities for devising tests of the Kerr metric. In this talk, I will show how imaging and spectroscopic observations of accreting black-holes with current and future instruments can lead to the first direct test of the no-hair theorem with an astrophysical object. Continue reading… Testing the No-Hair Theorem with Astrophysical Black Holes – Dmitrios Psaltis |
Cosmological Constraints from Peculiar Velocities – Arthur Kosowski | Fri. October 29th, 2010 11:30 am-12:30 pm |
Peculiar velocities of galaxies and clusters are induced during the formation of structure in the universe via gravitational forces. As such, they provide a potentially powerful route to constraining both the growth of structure and the expansion history of the universe. Traditional methods of velocity determination have not yet been able to measure velocities at cosmological distances with sufficient accuracy to allow cosmological constraints. I will discuss two possible methods of measuring peculiar velocities: directly via the kinematic Sunyaev-Zeldovich effect for galaxy clusters, and using distance measurements of type-Ia supernovae in future large surveys. I will discuss measurement prospects, and show that upcoming probes of mean pairwise velocity will have the potential to plac significant constraints on both dark energy and modifications of gravity while limiting systematic errors Continue reading… Cosmological Constraints from Peculiar Velocities – Arthur Kosowski |
IR issues in Inflation – Richard Holman | Fri. October 15th, 2010 11:30 am-12:30 pm |
I review some problems involving IR divergences in de Sitter space that give rise to behavior such as secular growth of fluctuations and discuss the use of the Dynamical Renormalization Group as a tool to resum and reinterpret these divergences. Time permitting, I’ll also discuss some more recent work on the breakdown of the semiclassical approximation in de Sitter space. |
The Angular Distribution of the Highest-Energy Cosmic Rays – Andrew Jaffe | Tue. October 12th, 2010 11:30 am-12:30 pm |
TBA Continue reading… The Angular Distribution of the Highest-Energy Cosmic Rays – Andrew Jaffe |
Bulk viscosity and the damping of neutron star oscillations – Mark Alford | Fri. October 8th, 2010 11:30 am-12:30 pm |
How do we learn about the phases of matter beyond nuclear density? They are to be found only in the interior of neutron stars, which are inaccessible and hard to observe. One approach is through the oscillations of neutron stars, which depend on the viscosity of their interior. If the viscosity is low enough then “r-mode” oscillations arise spontaneously and cause the star to spin down. Finding fast-spinning stars therefore puts limits on the viscosity viscosity and hence on the possible phases present in the interior of the star. This talk discusses non-linear effects which arise for large amplitude “suprathermal” Continue reading… Bulk viscosity and the damping of neutron star oscillations – Mark Alford |
CMB in a Box – Raul Abramo | Tue. September 28th, 2010 11:30 am-12:30 pm |
First, I will show that the line-of-sight solution to cosmic microwave anisotropies in Fourier space, even though formally defined for arbitrarily large wavelengths, leads to position-space solutions which only depend on the sources of anisotropies inside the past light-cone of the observer. This happens order by order in a series expansion in powers of the visibility function. Second, I will show that the Fourier-Bessel expansion of the physical fields (including the temperature and polarization momenta) is superior to the usual Fourier basis as a framework to compute the anisotropies. In that expansion, for each multipole $l$ there is a discrete tower of momenta $k_{i,l}$ (not a continuum) which can affect physical observables, |
Does Quantum Mechanics Imply Gravity? – Harsh Mathur | Tue. September 21st, 2010 11:30 am-12:30 pm |
TBA Continue reading… Does Quantum Mechanics Imply Gravity? – Harsh Mathur |
Galileon Inflation and Non-Gaussianities – Andrew Tolley | Tue. September 7th, 2010 11:30 am-12:30 pm |
I will discuss a new class of inflationary models based upon the idea of Galileon fields, scalar fields that exhibit non-linearly realized symmetries. These models predict distinctive non-Gaussian features in the primordial power spectrum, and I will discuss how they relate with, and can be distinguished from, canonical inflation, k-inflation, ghost inflation, and DBI-inflationary models. Continue reading… Galileon Inflation and Non-Gaussianities – Andrew Tolley |