June 29, 2018 | 12:00 PM | ERC 401 | Friday noon seminar Mapping the Milky Way in 6D with Gaia Jo Bovy, The University of Toronto
One of the main goals of Gaia, a new astrometric satellite mission, is to provide an empirical measurement of the distribution of stars in the 6+N dimensional space of position, velocity, age, mass, elemental abundances, color, magnitude, etc.. Knowledge of this empirical distribution will allow the formation, evolution, and dynamics of the Milky Way to be strongly constrained. I will give an overview of the Gaia mission and discuss novel methods to map the Milky Way in position and velocity using the billion-star Gaia catalog. I will then discuss results on the stellar content and dynamics of the solar neighborhood from applying these techniques to Gaia's first and second data release. I will also discuss the implications of the structure in the velocity distribution in the extended solar neighborhood observed in Gaia's second data release.
August 15, 2018 | 1:00 PM | ERC 401 | Special seminar Optimal CMB Lensing Reconstruction and Improved Constraints on Primordial Gravitational Waves Marius Millea, IAP
The next generation of CMB experiments are slated to measure the CMB polarization to noise levels and angular resolutions never before probed. One of the most exciting and revolutionary possibilities for this data would be a discovery of the non-zero tensor-to-scalar ratio $r$, i.e. the first detection of the background of gravitational waves produced by inflation. These gravitational waves are detectable via their impact on CMB B-mode polarization, however the B-modes are also significantly contaminated by the effects of gravitational lensing. Removing this lensing-induced B-mode foreground (called "delensing") will be necessary to obtain the tightest possible constraints on $r$. While at present-day noise levels, so-called "quadratic estimator" techniques have been massively successful in estimating and removing the lensing contamination, they become statistically sub-optimal at the noise-levels of even very near-future experiments. It is an open question how to improve upon them, and an exciting one because the potential is to shrink the error bar on $r$ by factors of a few, maybe turning a few-sigma hint of gravitational waves into a full blown discovery! In this talk, I will discuss an optimal Bayesian delensing method which we've developed to solve this problem. In the spirit of this being very much ongoing work, I will tell you about both successes we have had but also roadblocks and outstanding issues. Ultimately, this method can yield not only improved constraints on $r$, but also yield better reconstructions of the lensing potential which can be used in cross-correlations with various other low-redshift probes of structures.
September 21, 2018 | 1:00 PM | ERC 401 | Special seminar From the Accelerating Universe to Accelerating Science Robert Kirshner, Clowes Research Professor of Science, Harvard University Chief Program Officer for Science, Gordon and Betty Moore Foundation
Twenty years ago, astronomers were astonished to learn from observations of exploding stars that cosmic expansion is speeding up. We attribute this to a mysterious “dark energy” that pervades the universe and makes up 70% of it. Scientists are working in many ways to learn more about the nature of dark energy, but our reservoir of ignorance is deep. This talk will summarize the present state of knowledge and look ahead to new ways to use infrared observations of supernovae to improve our grip on dark energy. Accelerating scientific discovery is a mission of the Gordon and Betty Moore Foundation and I will illustrate some of the ways we do that in Chicago and beyond.
July 5, 2018 | 3:00 PM | PRC 201 | Open Group seminar Electroweak Baryogenesis through varying Yukawas in Composite Higgs models Sebastian Bruggisser, DESY
Varying Yukawas open new possibilities for electroweak baryogenesis. In this talk I will start by introducing varying Yukawas as a source of CP-violation and explain how baryogenesis can be successful in this framework. I will then present a realization of this paradigm in Composite Higgs models with partial compositeness. Composite Higgs models are, apart from the usual benefits, particularly compelling for this scenario as they feature an intimate link between flavour and Higgs physics. We will see that baryogenesis can be successful in these models if the confinement phase transition happens at the same time as the electroweak phase transition. I will identify regions in parameter space where this is fulfilled and I will compute the baryon yield of those models.
July 26, 2018 | 12:00 PM | ERC 401 | Open Group seminar Dark Energy with Euclid Santiago Casas, CEA Paris-Saclay
Euclid is an ESA medium-class mission expected to launch in 2022 that will map the geometry of the Universe by imaging 109 galaxies and measuring 107 galaxy redshifts in 15000 square degrees of the sky. This will provide us detailed information about the accelerated expansion, the evolution of large-scale structure and the matter-energy content of the Universe up to a redshift of about z ≈ 2. In this talk, I will review how the main probes of Euclid, namely galaxy clustering and weak lensing, will be able to constrain theories beyond the standard cosmological ΛCDM model and how we will be able to pin down the equation of state of dark energy with about 1% precision. Galaxy clustering measures mainly the movement of tracers along geodesics, while weak lensing is an almost direct mapping of the gravitational potentials at large scales. Using both of these observables, we can obtain valuable information about the growth of perturbations and the geometrical quantities of the Universe and therefore constrain the properties of General Relativity. Since the measurements of Euclid will also give insights on the properties of dark matter and neutrinos at cosmological scales, I will also show how we can measure non-standard couplings between matter species and dark energy and how we can give tight constraints on many alternative theories of gravity.
September 17, 2018 | 10:30 AM | ERC 419 | Open Group seminar Analytic IR-resummation for the BAO peak Matt Lewandowski, IPhT
We develop an analytic method for implementing the IR-resummation of 1404.5954, which allows one to correctly and consistently describe the imprint of baryon acoustic oscillations (BAO) on statistical observables in large-scale structure. We show that the final IR-resummed correlation function can be computed analytically without relying on numerical integration, thus allowing for an efficient and accurate use of these predictions on real data in cosmological parameter fitting. In this work we focus on the one-loop correlation function, where the challenge is to reproduce the BAO peak. We show that, compared with the standard numerical integration method of IR-resummation, the new method is accurate to better than 0.2%, and is quite easily improvable. We also give an approximate resummation scheme which is based on using the linear displacements of a fixed fiducial cosmology, which when combined with the method described above, is about six times faster than the standard numerical integration. Finally, we show that this analytic method is generalizable to higher loop computations.
July 9, 2018 | 12:00 PM | ERC 501 | Special Seminar The Drunken Trek of Ultra-High-Energy Cosmic Rays Through The Magnetic Field of the Milky Way Vasiliki Pavlidou, University of Crete
Cosmic rays are charged so that the magnetic field of the galaxy acts as a distorting lens to our view of the ultra-high-energy cosmic ray sky. I will discuss how we can reconstruct this lens and use it to our advantage to investigate both where cosmic rays come from, and what their composition is.