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Colloqiua & Seminars
Colloquia & Seminars, 2018
Current and Future Colloquia & Seminars, 2018
Past Colloquia & Seminars, 2018
Fundamental Physics with the Simons Observatory
Brian Keating, UC San Diego
The Simons Observatory is a new cosmic microwave background experiment being built on Cerro Toco in Chile, due to begin observations in the early 2020s. I will describe the scientific goals of the experiment, motivate its design, and forecast its performance. The Simons Observatory will measure the temperature and polarization anisotropy of the cosmic microwave background with arcminute resolution over approximately 40% of the sky in six frequency bands: 27, 39, 93, 145, 225 and 280 GHz. In its initial phase, three small-aperture (0.5-meter diameter) telescopes and one large-aperture (6-meter diameter) telescope will be fielded. These instruments will host a total of 60,000 cryogenic bolometer detectors. I will discuss some of the key science goals of the Simons Observatory, including the characterization of primordial fluctuations, determination of the number of relativistic species, and measuring the mass of neutrinos. I will also discuss other tests of fundamental physics -- some of which may be best measured using Cosmic Microwave Background observations such as the ones we are embarking upon.
Silvia Galli, Institut D'Astrophysique de Paris
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.
Imaging supermassive black holes with the Event Horizon Telescope
Friday noon seminar
Lindy Blackburn, Harvard-Smithsonian CfA
The Event Horizon Telescope is an expanding global array of sub-mm radio telescopes designed to directly probe the spacetime geometry and radiative processes on event-horizon scales for the supermassive black holes at the center of our galaxy, Sgr A*, and at the center of M87. A major goal of the EHT is to measure the size and shape of the black hole "shadow," a characteristic signature of strong lensing at the event-horizon and a fundamental prediction of general relativity. In 2017, the EHT operated an 8-station array with both the South Pole Telescope and the ALMA array in Chile for the first time, and included a coordinated campaign of simultaneous ground and space-based multiwavelength observations. While analysis is ongoing, the data achieve an unprecedented 20 micro-arcsecond resolution and provide a direct view of the spatial structure of dynamical processes in the immediate vicinity of Sgr A*.
Beyond the Boost
Siavash Yasini, University of Southern California
Our peculiar motion with respect to the cosmic microwave background (CMB) changes the observed frequency and incoming angle of the CMB photons due to the Doppler and aberration effects. The most prominent signature of these motion-induced effects on the CMB is a kinematic dipole, which is observationally indistinguishable from any intrinsic dipole that the CMB might possess. Due to this degeneracy -- and the fact that we theoretically expect the intrinsic dipole of the CMB to be subdominant with respect to the kinematic component -- the 3mK dipole of the CMB is commonly interpreted as an entirely kinematic effect. Consequently, the frame in which the entire dipole of the CMB vanishes is customarily defined as the CMB rest frame. However, if the intrinsic dipole of the CMB is non-zero, this definition would not be appropriate anymore, unless we can properly separate the intrinsic and kinematic components of the dipole. In this talk, I will demonstrate how we can achieve this goal using spectral measurements of the monopole and quadrupole moments of the CMB. I will also describe the impact of the Doppler and aberration effects on the CMB power spectrum (especially on the small angular scales) and their relevance as an observational bias for the current and future surveys. Our recently developed "Generalized Doppler and Aberration Kernel" formalism can be used to measure and remove the motion-induced effects from any arbitrary frequency-dependent cosmological observable.
The Progenitor of the Milky Way's Halo
Friday noon seminar
Vasily Belokurov, University of Cambridge/CCA, NYC
We map the composition of the Galactic stellar halo in 7 dimensions spanned by phase-space coordinates and chemical abundances. The local halo appears to be dominated by stars on highly eccentric orbits. These stars are more metal-rich than typically assumed for the Galactic halo and were likely deposited into the Milky Way during an ancient massive accretion event. Using numerical simulations of the stellar halo formation we deduce that this merger must have happened between 8 and 11 Gyrs ago, during the epoch of the Galactic disk formation. This formation scenario for the MW halo has a number of implications for the studies of the evolution of the Galaxy in general and the measurements of the local Dark Matter matter distribution in particular.
The State of Small-Scale "Crises" In Dark Matter
Philip F Hopkins, California Institute of Technology
The most fundamental unsolved problems in star and galaxy formation revolve around "feedback" from massive stars (and black holes). I'll review how new generations of theoretical models combine new numerical methods and physics, to try to realistically model the diverse physics of the ISM, star formation, and feedback, on a wide range of scales from those of individual proto-stars to the inter-galactic medium. Feedback produces galactic outflows and perturbs galactic structure in ways which fundamentally perturb the nature of dark matter cores and 'cusps', re-shaping rotation curves and suppressing the central densities of low-mass galaxies. I'll discuss a variety of small-scale "crises" in cold dark matter models: "cusp-core," "missing satellites," "too big to fail," and more, and show that these "crises" tend to simply vanish as higher resolution and more treatments of known physics are included in simulations. However, I will show that there are robust, testable predictions of CDM as compared to other models such as self-interacting or ultra-light scalar field or "warm" dark matter, but these may require fundamentally new observations.
The early Universe: preparing theory for observations
Friday noon seminar
Emanuela Dimastrogiovanni, Case Western Reserve University
I will describe some interesting scenarios for the generation of gravitational waves from inflation and their characteristic imprints, which can be tested with upcoming B-mode observations as well as with interferometers. In the second part of my talk I provide an overview of the physics of CMB spectral distortions and discuss what we can learn from those about the early universe.
Microwave Multiplexing of Superconducting Sensors
John A B Mates, University of Colorado, Boulder
Superconducting detectors provide by far the most sensitive measurement of long-wavelength radiation for astronomy and cosmology, with detector noise falling below that of the astronomical signals in the mid-to-late 1990s, depending on the wavelength of interest. To measure better and faster, we have therefore assembled cameras with increasingly large arrays of detectors.
Since the 90s, the size of superconducting detector arrays has followed a Moore's Law trend, which is set to continue into the 100,000 pixel range with instruments like the Simons Observatory and CMB-S4. Perhaps the greatest challenge to continuing this trend is the need to bring the signals from the detector arrays out of a 100 mK cryostat on a much smaller number of wires.
I will present the emerging technique of multiplexing these superconducting sensors using superconducting microresonators. We can use this new scheme with both superconducting Transition-Edge Sensors (TESs) and Microwave Kinetic Inductance Detectors (MKIDs) to read out thousands of highly-sensitive detectors per coaxial cable. This capability will enable new instruments for astronomy and precision cosmology.
Simulating structure formation in different environments and the applications
Chi-Ting Chiang, C.N. Yang Institute for Theoretical Physics/Stony Brook University
The observables of the large-scale structure such as galaxy number density generally depends on the density environment (of a few hundred Mpc). The dependence can traditionally be studied by performing gigantic cosmological N-body simulations and measuring the observables in different density environments. Alternatively, we perform the so-called "separate universe simulations", in which the effect of the environment is absorbed into the change of the cosmological parameters. For example, an overdense region is equivalent to a universe with positive curvature, hence the structure formation changes accordingly compared to the region without overdensity. In this talk, I will introduce the "separate universe mapping", and present how the power spectrum and halo mass function change in different density environments, which are equivalent to the squeezed bispectrum and the halo bias, respectively. I will then discuss the extension of this approach to inclusion of additional fluids such as massive neutrinos. This allows us to probe the novel scale-dependence of halo bias and squeezed bispectrum caused by different evolutions of the background overdensities of cold dark matter and the additional fluid. Finally, I will present one application of the separate universe simulations to predict the squeezed bispectrum formed by small-scale Lyman-alpha forest power spectrum and large-scale lensing convergence, and compare with the measurement from BOSS Lyman-alpha forest and Planck lensing map.
Primordial Black Holes in the era of Planck and LIGO
Friday noon seminar
Yacine Ali-Haimoud, New York University
LIGO's first direct gravitational-wave detections have revived interest in an old dark-matter candidate, primordial black holes (PBHs).
In this talk I will first discuss cosmic microwave background constraints to PBHs in the range of ~10 to a few hundred solar masses.
I will then discuss PBH binary formation processes and the resulting merger rates. In particular, I will argue that LIGO may already set the most stringent limits on PBH abundance, provided PBH binaries formed in the early Universe are not strongly perturbed by tidal fields due to non-linear structures.
Preliminary Cosmology Results from the Dark Energy Survey Supernova Program
Rick Kessler, The University of Chicago
We have recently completed 5 seasons of the Dark Energy Survey (DES), and cosmology results starting coming out last summer. Here I will discuss new cosmology results based on a subset of spectroscopically confirmed SNIa, and describe advances in the analysis aimed for much larger samples in DES and beyond. Finally, I will briefly describe other science projects using the DES transient-search pipeline.
Habitability of water-rich exoplanets
Friday noon seminar
Nadejda Marounina, University of Chicago
Planets with global water oceans have been the subject of intrigue both in Hollywood and in the exoplanet community. Water worlds are water-rich exoplanets that possess >1% of water by mass, and if located at an appropriate orbital separation from their host star, they may host a global surface water ocean. These habitable (liquid ocean-bearing) water worlds are especially timely because 1) water worlds formed from remnant cores of evaporated mini-Neptunes could be one of the dominant formation mechanisms for volatile-rich habitable zone planets around M dwarf stars, and 2) their larger sizes relative to terrestrial planets make them more amenable to observations with current and upcoming telescopes such as Hubble Space Telescope (HST) and James Webb Space Telescope (JWST). The recent and exciting discovery of TRAPPIST-1 system, that may possess planets with a substantial water/ice fraction, further motivates the study of water-worlds.
In the first part of this talk, I propose to give an overview on the habitability of water-worlds and show you that the the classical estimation of the habitable zone does not apply to this type of exoplanets. In the second part of my talk, I will present the coupled models of planet interiors, clathrate formation, liquid-vapor equilibrium, and atmospheric radiative transfer that are used constrain the atmospheric abundance of CO2 and corresponding habitable zone boundaries of water world exoplanets.
Science, Politicians, and the Public: What's the Story?
Rush D Holt, AAAS
With many public decisions being made on the basis of political partisanship rather than scientific evidence, what storyline should scientists follow and what difference does it make for the practicing researcher?
Galaxy Cluster Cosmology with the Dark Energy Survey
Yuanyuan Zhang, Fermilab
Constraining LambdaCDM cosmology with galaxy cluster abundance is one of the fundamental goals of the Dark Energy Survey (DES). Many thousands of clusters out to redshift 0.65 have been identified in DES data. Weak lensing and multi-wavelength studies with X-ray and cosmic microwave background observations are performed to provide inputs to the cosmology analysis. A cosmology pipeline that considers various systematic effects such as cluster projections and mis-centering is used to derive constraints on LambdaCDM cosmology parameters. In this talk, I will present current progress on DES galaxy cluster cosmology analyses as well as discuss future improvements.
Gauge-field inflation and the origin of the matter-antimatter asymmetry
Peter Adshead, University of Illinois at Urbana-Champaign
The basic inflationary paradigm is in good shape. On the one hand, the observed density fluctuations are adiabatic, gaussian and are red-tilted---characteristics in general agreement with simple models built from scalar fields. On the other hand, B-mode polarization of the cosmic microwave background sourced by primordial gravitational waves, the so-called smoking-gun signature of inflation, remains elusive. Upcoming and planned experiments will make increasingly precise B-mode measurements, potentially putting the inflationary paradigm through a stringent test.
In this talk, I describe a new class of inflationary scenarios which utilize gauge fields to generate inflationary dynamics in the early universe. Beyond simply providing yet another model for inflation, these scenarios furnish unique observational imprints which distinguish them from standard scalar-field scenarios. In particular, these scenarios generically result in large-amplitude, chiral gravitational waves and provide counterexamples to the standard claim that an observable tensor-to-scalar ratio requires inflation at the grand unification scale, as well as super-Planckian excursions of the inflaton. In addition I discuss how these chiral gravitational waves may be responsible for the matter-antimatter asymmetry of the Universe.
Dark Matter in the Universe
Katherine Freese, University of Michigan
"What is the Universe made of?" This question is the longest outstanding problem in all of modern physics, and it is one of the most important research topics in cosmology and particle physics today. The bulk of the mass in the Universe is thought to consist of a new kind of dark matter particle, and the hunt for its discovery in on. I'll start by discussing the evidence for the existence of dark matter in galaxies, and then show how it fits into a big picture of the Universe containing 5% atoms, 25% dark matter, and 70% dark energy. Neutrinos only constitute ½% of the content of the Universe, but much can be learned about neutrino properties from cosmological data. Leading candidates for the dark matter are Weakly Interacting Massive Particles (WIMPs), axions, and sterile neutrinos. WIMPs are a generic class of particles that are electrically neutral and do not participate in strong interactions, yet have weak-scale interactions with ordinary matter. There are multiple approaches to experimental searches for WIMPS: at the Large Hadron Collider at CERN in Geneva; in underground laboratory experiments; with astrophysical searches for dark matter annihilation products, and upcoming searches with the James Webb Space Telescope for Dark Stars, early stars powered by WIMP annihilation. Current results are puzzling and the hints of detection will be tested soon. At the end of the talk I'll briefly turn to dark energy and its effect on the fate of the Universe.
Innovations in Big Data and HPC for Cosmology
Deborah Bard, NERSc, LBNL
Cosmological ''big data'' problems go beyond the simple volume of data stored on disk. Our observations of the universe are necessarily finite, and the challenge we face is how we can extract the maximum amount of information from the observations and simulations we have available to us.
High Performance Computing (HPC) is increasingly being used to enable complex analyses that were previously inaccessible to scientists. NERSC is the mission computing center for the DOE Office of Science, and we sit at the intersection of HPC, algorithmic development and cutting-edge science. I will discuss some of the cosmology projects we lead in this space, such as Galactos (calculating the anisotropic three-point correlation function for 20 billion galaxies), Celeste (cataloguing the visible universe through Bayesian inference using Julia), CosmoGAN (developing a cosmological emulator using generative adversarial networks) and CosmoFlow (learning the structure of the universe through 3D deep learning techniques).
These projects showcase a combination of computer science, HPC advances and real problems in cosmology, with the overarching theme of how we can scale computing tools (including machine learning and inference) to enable new techniques in data analysis, and to accelerate time-to-discovery.
Discovering the Highest Energy Neutrinos Using a Radio Phased Array
Abby Vieregg, The University of Chicago
Ultra-high energy neutrino astronomy sits at the boundary between particle physics and astrophysics. The detection of high energy neutrinos is an important step toward understanding the most energetic cosmic accelerators and would enable tests of fundamental physics at energy scales that cannot easily be achieved on Earth. IceCube has detected astrophysical neutrinos at lower energies, but the best limit to date on the flux of ultra-high energy neutrinos comes from the ANITA experiment, a NASA balloon-borne radio telescope designed to detect coherent radio Cherenkov emission from cosmogenic ultra-high energy neutrinos. The future of high energy neutrino detection lies with ground-based radio arrays, which would represent an large leap in sensitivity. I will discuss a new radio phased array design that will improve sensitivity enormously and push the energy threshold for radio detection down to overlap with the energy range probed by IceCube.
Project 8: Towards a Direct Measurement of the Neutrino Mass with Tritium Beta Decays
Noah S Oblath, Pacific Northwest National Laboratory
Cyclotron Radiation Emission Spectroscopy, a frequency-based method for deter- mining the energy of relativistic electrons, has recently been demonstrated by the Project 8 collaboration. Applying this technique to the tritium endpoint provides a new avenue for measuring the absolute mass-scale of the neutrino. The proof of principle was done in a small waveguide detector using gaseous 83mKr as a source of monoenergetic electrons. As the next step towards a neutrino mass measurement, we are upgrading the existing detector to operate using a molecular tritium source, and to have enhanced radiofrequency properties. These upgrades are the next research and development steps needed to design a larger scale experiment that will approach the existing neutrino mass limits. I will discuss the expected physics reach of this second phase of Project 8 with molecular tritium, based on data from its commissioning with 83mKr. I will also present the plans for Phases III and IV, and the challenges being addressed for each phase.
The impact of massive neutrinos on cosmological observables
Francisco Villaescusa-Navarro, Center for Computational Astrophysics
Neutrinos are one of the most mysterious particles in nature. The discovery that they are massive has revolutionized our understanding of fundamental physics. Unfortunately, we still don't know their nature, masses or hierarchy. A worldwide effort is underway trying to answer these questions through laboratory experiments. In this seminar I will show how neutrino's unique nature leaves signatures on many different cosmological observables such as the properties of matter, halos, galaxies, voids, redshift-space distortions, the Lya-forest, baryonic acoustic oscillations and 21cm. I will discuss how those signatures can be used to weigh neutrinos and what are the main problems to obtain an unbiased measure of their masses.
High redshift 21cm intensity mapping Past, Present, and Future
Daniel Jacobs, Arizona State University
The redshifted 21 cm line from neutral hydrogen provides a direct, cosmological scale, probe of the epochs of reionization and heating. In the past decade, multiple experimental arrays have worked towards detection and characterization of this spectral line signal at redshifts 6 and higher. HERA is a second generation instrument probing 21cm emission and absorption at redshifts from 6 to 20. The use of large static dishes provides sensitivity which is predicted to be roughly an order of magnitude larger than first generation experiments while advances in instrumentation and technique aim for reduced foreground contamination. The raw sensitivity provided by dishes is high enough that forecasts of astrophysical parameter constraint precision is limited mainly by model uncertainty not sensitivity, and that for the first time direct imaging of features is theoretically possible. HERA is proceeding with construction while observing in parallel with new dishes being added as they become available. The 2017-2018 observing season with 40 dishes is forecasted to have roughly double the sensitivity of previous experiments. Here we report the ongoing commissioning of this array and present early results of experiments in calibration and imaging.
Mass' not the only thing: Secondary effects in the galaxy-halo connection
Yao-Yuan Mao, University of Pittsburgh
Dark matter halos are the building blocks of our universe. The story we have been telling is that the galaxies live in halos, and that brighter galaxies live in bigger halos. This story is mostly consistent with our observation and hydrodynamical simulations, and has shed light on our understandings of galaxy formation and evolution. However, it is also clear that this simple, zeroth-order galaxy-halo connection is not the whole story. The assembly history of halos affects the galaxies reside in, and also affects the clustering properties of halos. This effect, usually known as "assembly bias," has brought new challenges to our ability to accurately model the galaxy-halo connection. A class of galaxy-halo connection models that take assembly bias into account has emerged, but it at the same time highlights the complex nature of assembly bias. In this talk I will discuss a few different aspects of assembly bias, focusing on how it affects the galaxy-halo connection and also its implications.
Citizen Science Frontiers: Efficiency, Engagement, and Serendipitous Discovery with Human-Machine Systems
Laura Trouille, The Adler Planetarium and Northwestern University
The Zooniverse is the world's largest and most successful scientific crowdsourcing platform, engaging more than 1.6 million volunteers in tasks including classifying galaxies, discovering planets, transcribing artist's notebooks, and tracking resistance to antibiotics. Processing our increasingly large datasets poses a bottleneck for producing real scientific outcomes. Citizen science - engaging the public in research - provides a solution, particularly when coupled with machine learning algorithms and sophisticated task allocation. Faced with a rapidly growing demand for citizen science projects, Zooniverse launched its 'Project Builder' which allows you, the researcher, to build your own project in-house for free using the Zooniverse infrastructure and tools. In this talk I will discuss the frontiers of citizen science, including Zooniverse innovations in human-machine integration coupled with community engagement -- and the related open questions. I will also provide a brief tutorial on building your own crowdsourcing project.
Discussion on old and new mechanisms of leptogenesis
Jessica M Turner, Fermi National Accelerator Laboratory
In the first half of the talk, I will present preliminary results which indicate the scale of thermal leptogenesis may be several orders of magnitude lower than previously thought.
In the second half of this talk I will present a mechanism of leptogenesis which is based on the vacuum CP-violating phase transition. This approach differs from classical thermal leptogenesis as a specific seesaw model, and its UV completion, need not be specified. The lepton asymmetry is generated via the dynamically realised coupling of the Weinberg operator during the phase transition. This
mechanism provides strong connections with low-energy neutrino experiments.
Topics in weak lensing
Patricia Larsen, Argonne National Laboratory
Gravitational weak lensing has emerged in recent years as a powerful probe of cosmology, giving important constraints on both dark and luminous matter. This has led to a number of ambitious future surveys, which promise to revolutionise the field if theoretical challenges can be met. In this talk I will discuss some of my recent work in the field of weak lensing, spanning a range of topics including combined probe analysis, intrinsic alignment contamination and delensing.
From Emergent Gravity to Dark Energy and Dark Matter
Erik P. Verlinde, University of Amsterdam
The observed deviations from the laws of gravity of Newton and Einstein in galaxies and clusters can logically speaking be either due to unseen dark matter or due to a change in the way gravity works. Until recently there was little reason to doubt that general relativity correctly describes gravity in these circumstances. In the past few years insights from black hole physics and string theory have lead to a new theoretical framework in which the gravitational laws are derived an underlying microscopic quantum description of spacetime. An essential ingredient in the derivation of the Einstein equations is that the quantum entanglement of the vacuum obeys an area law, a condition that is known to hold in Anti-de Sitter space. In a Universe that is dominated by positive dark energy, like de Sitter space, the microscopic entanglement entropy contains, in addition to the area law, a volume law contribution whose total contribution equals the Bekenstein-Hawking entropy associated with the cosmological horizon. We will argue that this extra volume law contribution leads to modifications in the emergent laws of gravity, and provide evidence for the fact that these modifications explain the observed phenomena in galaxies and clusters currently attributed to dark matter. We end with a discussion of the possible implications for early cosmology, the CMB and structure formation.