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Colloqiua & Seminars
Past Colloquia & Seminars
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.
Towards Accurate Cosmology with Galaxy Lensing Surveys
Friday noon seminar
Ami Choi, The Ohio State University
Ongoing wide area galaxy surveys are producing large volumes of data, placing
impressive constraints on our cosmological understanding of the
Universe, even rivaling the precision delivered by cosmic microwave
background (CMB) experiments. The statistical power of the available data sets
can only be harnessed with careful control of potential sources of systematic
error that can affect both the observational measurements and the theoretical
modelling. I will set the scene by describing current results from the Kilo-Degree
Survey (KiDS) and the Dark Energy Survey (DES), both of which have recently completed
intricate analyses combining different measurements of weak gravitational
lensing and galaxy clustering. I will discuss how we can characterize some of the
more precarious moving parts of the analysis (e.g. photometric redshifts) with
information from overlapping spectroscopic and CMB
data sets. I will conclude with a look forward to a bright future with the Wide-Field
Infrared Survey Telescope and the Large Synoptic Survey Telescope.
The not so boring ultra-high energy cosmic ray sky
Edivaldo Moura Santos, University of San Paolo
After more than 12 years of continuous data taking, the Pierre Auger Observatory has collected the largest dataset of ultra-high energy cosmic rays (UHECR) to date. It combines a set of fluorescence telescopes to measure the tiny emission of light from air molecules excited by the passage of air showers and an array of ground based water Cherenkov tanks to sample the shower particles at the ground level, Such a hybrid detection system has allowed a redundancy in reconstruction variables as well as the elimination of large systematic uncertainties associated to the absolute energy scale of atmospheric cascades through a data-driven cross-calibration procedure between the two detectors. The results obtained in the last years include, for example, precise and accurate measurements of the UHECR flux across a few decades in energy, revealing distinctive spectral features that can bring valuable information on different astrophysical processes like: the transition from galactic to extragalactic fluxes; the different energy loss processes to which ultra-relativistic charged particles are subject during their propagation; the energetics of the production and acceleration of particles at the candidate sources. In this colloquium I should however focus on a particular observational probe, that is, the small levels of anisotropy in the flux of UHECR at different angular scales: from the small and intermediate ones, important for the identification of possible point sources, to the large angular scales, usually used to search for signs of the galactic to extragalactic transition. In particular, special attention will be devoted to the first observation of a large scale anisotropy signal at the highest energies recently reported by the collaboration.
Excluding a thin dark matter disk in the Milky Way with Gaia DR1
Katelin Schutz, UC Berkeley
If a component of the dark matter has dissipative interactions, it could collapse to form a thin dark disk in our Galaxy coincident with the baryonic disk. It has been suggested that dark disks could explain a variety of observed phenomena, including mass extinction events due to periodic comet impacts. Using the first data release from the Gaia space observatory, I will present the results of a search for a dark disk via its effect on stellar kinematics in the Milky Way. I will discuss our strong new limits that disfavor the presence of a thin dark matter disk and present updated measurements on the total matter density in the solar neighborhood.
Clarifying the Hubble constant tension
Stephen Feeney, Flatiron Institute
Hubble constant estimates from measurements of the local distance ladder and the cosmic microwave background (assuming a flat LCDM cosmology) are discrepant at the 2.8 to 3.4-sigma level. Interpreting this tension correctly requires a model-comparison calculation which depends strongly on the precise tails of the likelihoods in addition to the traditional ''n-sigma'' discrepancy. This model-comparison approach requires evaluation of the full distance-ladder likelihood, as opposed to a Gaussian or least-squares approximation to it. I will discuss our reframing of the distance ladder as a Bayesian Hierarchical Model (BHM), in which the Cepheids and supernovae (SNe) that comprise the ladder are fitted simultaneously and self-consistently. This highly flexible framework incorporates non-Gaussian anchor measurements, marginalizes over all relevant nuisance parameters and allows the use of heavy-tailed intrinsic scatter distributions to obtain robust inferences even in the presence of outliers, without resorting to unstable clipping methods. Using this BHM, I will clarify the Hubble constant tension by comparing LCDM to a model designed to predict the observed discrepancy.
Journey to the Beginning of Time: Turning Metaphysics into Physics
Lawrence M Krauss, Arizona State University
Even a generation ago, fundamental existential questions such as, "How did the Universe Begin?, How will it End?, Are we Alone, and, Are there OTHER Universes?," and other less grand but no less interesting questions such as "Do Black Holes Exist?" may have appeared as forever inaccessible metaphysical questions. Gravitational waves have now been discovered by LIGO, opening up a vast new window on the Universe. I will explain how we might eventually unambiguously detect a gravitational signal from moments after the Big Bang, pushing our direct empirical handle on the Universe back in time by 49 orders of magnitude, and revealing what we might learn about own origins, the nature of gravity, grand unification, and even the possible existence of other universes.
Surprises in the small scale CMB
Simone Ferraro, UC Berkeley
Information about the late-time Universe is imprinted on the small scale CMB as photons travel to us from the surface of last scattering. Several processes are at play and small scale fluctuations are very rich and non-Gaussian in nature.
I will review some of the most important effects and I will focus on the Sunyaev-Zel'dovich (SZ) effect and gravitational lensing. I will discuss how a combination of measurements can probe velocity fields at cosmological distances, inform us on cluster energetics and feedback processes, and detect the properties of patchy reionization. If time allows, I will describe new approaches to CMB lensing reconstruction on small scales.
The status of sterile neutrino dark matter
Shunsaku Horiuchi, Virginia Tech
The sterile neutrino is a warm dark matter candidate with a host of observable signatures that have recently been sensitively tested. I will first review the sterile neutrino before introducing constraints arising from structure formation and high-energy astrophysics. These offer important complementarity in covering the sterile neutrino parameter space and I will highlight some of the recent rapid progress. I will also discuss ways forwards to test whether the 3.5 keV line detected in multiple dark matter concentrations may be arising from sterile neutrino dark matter.
Probing Cosmology with the Dark Energy Survey
Josh Frieman, The University of Chicago
I will overview the Dark Energy Survey (DES) project and highlight its early science results, focusing on the recently released cosmology results from the first year of the survey. The DES collaboration built the 570-megapixel Dark Energy Camera for the Blanco 4-meter telescope at NOAO's Cerro Tololo Inter-American Observatory in Chile to carry out a deep, wide-area, multi-band optical survey of several hundred million galaxies and a time-domain survey to discover several thousand supernovae. The survey started in Aug. 2013 and is now in its fifth observing season. DES was designed to address the questions: why is the expansion of the Universe speeding up? Is cosmic acceleration due to dark energy or does it require a modification of General Relativity? DES is addressing these questions by measuring the history of cosmic expansion and the growth of structure through multiple complementary techniques: galaxy clusters, the large-scale galaxy distribution, gravitational lensing, and supernovae, as well as through cross-correlation with other data sets. I will also discuss how the DES data are being used to make a variety of other astronomical discoveries, from the outer Solar System to ultra-faint dwarf galaxies to the kilonova counterpart of a binary neutron star gravitational-wave source.
Efficient Evaluation of Cosmological Statistics Using FFTLog
Marko Simonovic, Institute for Advanced Study
The FFTLog algorithm can be seen as a way to decompose the linear power spectrum onto a basis of complex power-law functions. On the other hand, many important integrals in cosmology that involve power spectra have simple analytical solutions for a power-law universe. In this talk I will show how to combine these two ideas in practice. I will discuss applications to evaluation of the angular power spectrum and bispectrum of arbitrary observables, as well as evaluation of the loop integrals in cosmological perturbation theory of large-scale structure.
The Limits of Cosmology
Joe Silk, IAP/JHU
One of our greatest challenges in cosmology is understanding the origin of the structure of the universe, and in particular the formation of the galaxies. I will describe how the fossil radiation from the beginning of the universe, the cosmic microwave background, has provided a window for probing the initial conditions from which structure evolved and seeded the formation of the galaxies, and the outstanding issues that remain to be resolved. I will address our optimal choice of future strategy in order to make further progress on understanding our cosmic origins.
Aspects of field theory with higher derivatives
Adam Solomon, University of Pennsylvania
I will discuss related aspects of field theories with higher-derivative Lagrangians but second-order equations of motion, with a focus on the Lovelock and Horndeski classes that have found use in modifications to general relativity. In the first half I will discuss how non-perturbative effects, like domain walls and quantum tunneling, are modified in the presence of these kinetic terms. In the second half I will investigate when restricting to such terms is and is not well-justified from an effective field theory perspective.
Machine Learning and Signal Processing for Weak Lensing Science: from galaxy image simulations to 3D mass maps
Francois Lanusse, Carnegie Mellon University
The next generation of large-scale cosmological surveys, such as LSST, WFIRST and Euclid, aim at answering fundamental questions on the nature of dark energy and dark matter by measuring the weak lensing signal (gravitationally induced deformation of galaxy images) over large areas of the sky. In this talk, I will illustrate how the most recent advances in Machine Learning and Statistical Signal Processing open new perspectives for addressing some of the challenges faced by these new surveys as well as exploiting this wealth of data in new and exciting ways. In particular, I will focus on our work with Deep Generative Models in two different settings: simulating realistic galaxy images for shape measurement calibration purposes, and modeling the intrinsic alignment signal (the tendency of galaxies to align with the large scale structure) in hydrodynamical simulations, with the aim of producing realistic mock galaxy catalogs. Both of these applications aim to address some of the main systematics of future wide field lensing surveys. Finally, I will present an application of sparse signal processing which makes possible the reconstruction of high-resolution 3D weak lensing mass maps, with the ability to disentangle structures along the line of sight and resolve individual clusters.
First observation of coherent elastic neutrino-nucleus scattering
Grayson C Rich, Triangle Universities Nuclear Lab
The process of coherent elastic neutrino-nucleus scattering (CEvNS) was predicted in 1974 by D.Z. Freedman, who suggested that attempts to detect CEvNS “may be an act of hubris” due to several profound experimental challenges. More than 40 years after its initial description, the world’s smallest functional neutrino detector has been used by the COHERENT Collaboration to produce the first observation of the process: a 14.6-kg CsI[Na] scintillator was deployed to the Spallation Neutron Source of Oak Ridge National Lab and observed, with high significance, evidence for a CEvNS process in agreement with the prediction of the Standard Model. I will discuss CEvNS and its connection to a range of exciting physics, including: its potential role in supernova dynamics; the possibility to use neutrinos as a tool for studying nuclear structure and neutron stars; its relationship to upcoming direct searches for WIMP dark matter; and the ways in which CEvNS could offer insight into physics beyond the Standard Model. The experimental program and the recent result from the COHERENT Collaboration will be presented along with ongoing efforts within the collaboration and future plans.