October 3, 2018 | 3:30 PM | ERC 161 | Wednesday colloquium Cosmological results from the final data release of the Planck satellite Silvia Galli, IAP
Video Planck is an ESA satellite aimed at the observation of the Cosmic Microwave Background. This year, the Planck collaboration has released its final data and results. In this talk, I will describe the main results on cosmology from the mission, highlighting the changes with respect to previous releases, the agreement with other cosmological probes and the unsolved questions opened for the future.
October 10, 2018 | 3:30 PM | ERC 161 | Wednesday colloquium Fundamental Physics with the Simons Observatory Brian Keating, UC San Diego
Video Brian Keating 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.
October 17, 2018 | 3:30 PM | ERC 161 | Astronomy Colloquium Compact Binaries and the Origin of Millisecond Pulsars Jay Strader, Michigan State University
It is well-established that fast-spinning millisecond pulsars are neutron stars recycled through accretion from binary companions. For most millisecond pulsars the accretion process has permanently ceased, and they are in binary systems with low-mass white dwarf companions. Follow-up observations of newly discovered gamma-ray sources from the Fermi Gamma-Ray Space Telescope have revealed a substantial population of "spider" millisecond pulsars with hydrogen-rich companions; these systems had mostly been missed in radio pulsar surveys. I will discuss the properties of neutron stars in these binaries and and the implications for the formation and evolution of millisecond pulsars.
October 24, 2018 | 3:30 PM | ERC 161 | Astronomy Colloquium Galactic Archaeology in the Gaia Era Keith Hawkins, University of Texas at Austin
One of the key objectives of modern astrophysics is to understand the formation and evolution galaxies. In this regard, the Milky Way is a fantastic testing ground for our theories of galaxy formation. However, dissecting the assembly history of the Galaxy, requires a detailed mapping of the structural, dynamical chemical, and age distributions of its stellar populations. Recently, we have entered an era of large spectroscopic and astrometric surveys, which has begun to pave the way for the exciting advancements in this field. Combining data from the many multi-object spectroscopic surveys, which are already underway, and the rich dataset from Gaia will undoubtedly be the way forward in order to disentangle the full chemo-dynamical history of our Galaxy. In this talk, I will discuss my current work in Galactic archaeology and how large spectroscopic surveys have been used to dissect the structure of our Galaxy. I will also explore the future of Galactic archaeology through chemical cartography.
October 31, 2018 | 3:30 PM | ERC 161 | Astronomy Colloquium Juno's Hunt for Jovian Deep Oxygen, and the Implications for Giant Planet Formation Jonathan Lunine, Cornell University
The carbon-to-oxygen ratio (C/O) in giant planets is an important indicator of processes in disks that lead to planet formation. However, obtaining this ratio in Jupiter and Saturn is far more difficult than in hot exo-Jupiters, because water condenses out of the visible atmospheres of the solar system's two giants. For Jupiter, the Galileo Probe almost got us there, but Juno data are required to close in on the deep oxygen abundance. For other planetary systems, JWST will provide very high quality transit spectra that will allow us to see the carbon- and oxygen-bearing species in many giant planets around other stars.
November 7, 2018 | 3:30 PM | ERC 161 | Wednesday colloquium Dark Energy: The Cosmological Constant in the Skies Stephon Alexander, Brown University
Video After a pedagogical review of the cosmological constant problem and status of Dark Energy, I will present some new ideas, progress and challenges to account for the current acceleration of the universe and the smallness of the cosmological constant.
November 14, 2018 | 3:30 PM | ERC 161 | Astronomy Colloquium Microlensing Perspectives on Cool Planet Populations Jennifer Yee, Harvard University
Microlensing is uniquely capable of studying planets across a wide range of masses at a few AU from their host stars. At the lower masses, these planets are difficult to impossible to find with other techniques. I will discuss recent results in microlensing suggesting a turnover in the planet mass ratio function around 10^-4, i.e. that planets with mass ratios similar to Neptune are the most abundant at separations probed by microlensing. I will also discuss microlensing constraints on the free-floating planet population. Finally, I will discuss how current and future microlensing surveys, including WFIRST, will advance our understanding of cool planet populations.
November 28, 2018 | 3:30 PM | ERC 161 | Astronomy Colloquium How Long do Quasars Shine? Joe Hennawi, University of California - Santa Barbara
Luminous quasars are believed to be the progenitors of the supermassive black holes observed ubiquitously at the centers of all massive galaxies, but we are still in the dark about how these black holes actually formed. Our ignorance largely results from the fact that the expected timescale for supermassive black hole growth of 45 million years is much longer than the mere fifty years that humans have been observing quasars. A holy grail would thus be a direct measurement of quasar lifetimes, shedding light on the physical mechanisms responsible for fueling black hole growth, and how the back-reaction of this growth might influence how galaxies form. I will show how observations of diffuse intergalactic gas in the environs of luminous quasars can be used to chronicle the history of quasar emission on timescales from kiloyears to gigayears. I will also discuss how these same observations can be used to constrain the reionization history of the Universe.
December 5, 2018 | 3:30 PM | ERC 161 | Wednesday colloquium New Results from BICEP/Keck Colin Bischoff, University of Cincinnati
Video The BICEP/Keck series of telescopes make up a long-running program of small-aperture Cosmic Microwave Background polarimeters observing from the South Pole. I will describe new results that incorporate Keck Array observations from 2015, including our first 220 GHz data. These results improve the upper limit on the tensor-to-scalar ratio to r < 0.07 at 95% confidence and we explore the robustness of this constraint to complications in the dust foreground, instrumental systematics, and other variations in the analysis. The next steps forward in sensitivity will include 2016-2018 data from BICEP3 and Keck Array, followed by the four-telescope BICEP Array which will begin observing in 2020.
December 12, 2018 | 3:30 PM | ERC 161 | Wednesday colloquium Challenges for physical cosmology after Planck Matias Zaldarriaga, Institute for Advanced Study
Video I will discuss the current status of physical cosmology after the latest Cosmic Microwave Background and other measurements. I will discuss the questions that still remain open in the field and how we might go about answering them. I will describe some recent theoretical developments that might contribute useful tools for overcoming some of the challenges that lie ahead.
October 5, 2018 | 3:00 PM | ERC 576 | Friday noon seminar Neutrino cosmology and large scale structure Christiane Stefanie Lorenz, University of Oxford
In this talk, I will present studies of the model-dependence of cosmological neutrino mass constraints. In particular, I will focus on two phenomenological parameterizations of time-varying dark energy (early dark energy and barotropic dark energy) that can exhibit degeneracies with the cosmic neutrino background over extended periods of cosmic time. Moreover, I will show how the combination of multiple probes across cosmic time can help to distinguish between the two components. In addition, I will discuss how neutrino mass constraints can change in extended neutrino mass models, and how current tensions between low- and high-redshift cosmological data might be affected in these models. Finally, I will discuss whether lensing magnification and other relativistic effects that affect the galaxy distribution contain additional information about dark energy and neutrino parameters, and how much parameter constraints can be biased when these effects are neglected.
October 12, 2018 | 12:00 PM | ERC 401 | Friday noon seminar Massive Neutrinos, Galaxy Clusters and the Lyman-alpha Forest Simeon Bird, UC Riverside
I'll present new efficient and accurate techniques for including massive neutrinos in N-body simulations, using a linear response (to the cold dark matter) approximation for the neutrinos. Then I'll talk about the potential for massive neutrinos to resolve some cosmological tensions within CMB observations galaxy clusters. Finally, I'll discuss how to detect features in quasar spectra using machine learning.
October 19, 2018 | 12:00 PM | ERC 576 | Friday noon seminar Precision Cosmology with the Cosmic Microwave Background from Chile Sara M. Simon, University of Michigan
Image credit: Jon Ward
The cosmic microwave background (CMB) provides unparalleled views into the early universe and its later evolution. Recent and ongoing experiments have contributed to our understanding of neutrinos, dark energy, and dark matter through measurements of large scale structure imprinted on the CMB and constrained the conditions in the early universe, tightly restricting inflationary and other cosmological models through measurements of CMB polarization. Next-generation CMB experiments like Simons Observatory will further constrain the sum of the neutrino masses and number of relativistic species, expand our understanding of dark energy and dark matter, and set new constraints on cosmological models describing the first moments of the universe. The polarization in the CMB is faint, so future experiments must be orders of magnitude more sensitive. Additionally, both polarized foregrounds from synchrotron and dust emission and systematic effects from the instruments can create spurious polarization signals. Characterizing and removing foregrounds requires wide frequency coverage, while systematic effects must be modeled, mitigated and calibrated at unprecedented levels. I will discuss several advances in instrumentation and analysis that will be critical for this leap in performance.
November 2, 2018 | 11:00 AM | PRC 201 | Friday noon seminar Astrophysical applications of coherent neutrino scattering Louis Strigari, Texas A&M University
Neutrino-nucleus coherent scattering (CNS) is a long standing theoretical prediction of the Standard Model (SM), with experimental evidence for it just very recently being announced. CNS provides an important probe of physics beyond the SM, with a reach that can surpass the sensitivity of much larger scale detectors. In addition, it can open up a new window into neutrinoastrophysics, through studies of low energy neutrinos from the Sun, atmosphere, and supernovae. CNS is also vital for understanding and interpreting future particle dark matter searches. In this talk, I will discuss the prospects for learning about the nature of neutrinos and astrophysical sources from CNS detection, highlighting how astrophysical and terrestrial-based detections play important and complementary roles.
November 9, 2018 | 12:00 PM | ERC 576 | Friday noon seminar Superfluids and the Cosmological Constant Problem Jeremy Sakstein, University of Pennsylvania
The Lambda-CDM cosmological model is still the best-fit to current data, and numerous alternatives have recently been ruled out by the observation of gravitational waves and other small-scale probes. Theoretically, the cosmological constant (Lambda) suffers from a severe fine-tuning that needs to be understood in order for Lambda-CDM to be a satisfactory model. In this talk I will discuss a recent proposal for a model that may ameliorate the cosmological constant problem. In this model, a superfluid pervading the universe could counteract the large (unobserved) cosmological constant predicted by quantum mechanics. I will discuss the novel phenomenology predicted by the superfluid as well as future directions for testing this model.
November 16, 2018 | 12:00 PM | ERC 401 | Friday noon seminar Dark Matter in Disequilibrium and Implications for Direct Detection Lina Necib, Caltech
Using two realizations of the Milky Way from the FIRE simulation, we find that the kinematics of dark matter follows closely the kinematics of accreted stars from the same mergers. We use this correspondence to build an empirical local velocity distribution of dark matter, by analyzing the Gaia second data release coupled with the ninth release from the Sloan Digital Sky Survey, and computing the velocity distribution of the accreted stars. We find that this velocity distribution is peaked at lower velocities than the generally assumed Maxwell Boltzmann distribution, due to the presence of a recent merger referred to as the Gaia Sausage, leading to a weakening of direct detection limits at dark matter masses less than 10 GeV.
November 30, 2018 | 12:00 PM | ERC 401 | Friday noon seminar A Solution to the Cosmological Constant Problem Surjeet Rajendran, UC Berkeley
The discovery of Dark Energy, a mysterious source that drives the accelerated expansion of the universe has created a major theoretical conundrum: the measured value of the dark energy is at least 60 orders of magnitude smaller than known theoretical contributions to it. What is the physics responsible for this extra-ordinary cancellation? It has been known for a long time that conventional symmetry based ideas that are often used to explain small numbers and precise cancellations are experimentally ruled out as solutions to this problem. In this talk, I will present a solution to the cosmological constant problem, where the problem is solved through cosmic evolution. This solution features novel cosmologies such as a Big Bounce that replaces the conventional Big Bang picture of the early universe. I will also discuss experimental techniques to search for these solutions in the laboratory.
December 7, 2018 | 12:00 PM | ERC 401 | Friday noon seminar Searching for Dark Matter Interactions in Cosmology Kimberly Boddy, Johns Hopkins University
There is a substantial effort in the physics community to search for dark matter interactions with the Standard Model of particle physics. Collisions between dark matter particles and baryons exchange heat and momentum in the early Universe, enabling a search for dark matter interactions using cosmological observations in a parameter space that is highly complementary to that of direct detection. In this talk, I will describe the effects of scattering in the CMB power spectra and show constraints using Planck 2015 data, and I will discuss the implications of late-time scattering during the era of Cosmic Dawn.
December 14, 2018 | 12:00 PM | ERC 401 | Friday noon seminar Counting Stars: Developing Probabilistic Cataloging for Crowded Fields Stephen Portillo, University of Washington
The depth of next generation surveys poses a great data analysis challenge: these surveys will suffer from crowding, making their images difficult to deblend and catalog. Sources in crowded fields are extremely covariant with their neighbors and blending makes even the number of sources ambiguous. Probabilistic cataloging returns an ensemble of catalogs inferred from the image and can address these difficulties. We present the first optical probabilistic catalog, cataloging a crowded Sloan Digital Sky Survey r band image cutout from Messier 2. By comparing to a DAOPHOT catalog of the same image and a Hubble Space Telescope catalog of the same region, we show that our catalog ensemble goes more than a magnitude deeper than DAOPHOT. We also present an algorithm for reducing this catalog ensemble to a condensed catalog that is similar to a traditional catalog, except it explicitly marginalizes over source-source covariances and nuisance parameters. We also detail efforts to make probabilistic cataloging more computationally efficient and extend it beyond point sources to extended objects. Probabilistic cataloging takes significant computational resources, but its performance compared to existing software in crowded fields make it a enticing method to pursue further.
November 14, 2018 | 11:30 AM | ERC 445 | Open Group seminar The Tachyonic Instability in Scalar-Tensor Theories Jorgos Papadomanolakis, Lorentz Institute
In recent years the discovery of late-time cosmic acceleration triggered the creation of a landscape of extensions of General Relativity, aimed at providing a theoretical compelling mechanism. Now, with the wealth of current and upcoming observational data, it becomes imperative to find efficient ways to constrain these theories both from a theoretical as a data point of view. In this talk I will start by introducing the formalism of the Effective Field Theory of Dark Energy and Modify Gravity and will then proceed to employ it in order to study the theoretical stability of scalar extensions of gravity. I will pay special attention to the tachyonic instability, an instability seldom taken into account in the literature. This will yield powerful new constraints that severely impact the parameter space of gravitational theories. In the final part I will present how they impact the phenomenological (μ,Σ) parameter space, a result obtained by implementing the stability conditions in the Einstein Boltzmann solver EFTCAMB.
November 16, 2018 | 3:30 PM | ERC 401 | Open Group seminar N-body Cosmology with Abacus Garrison Lehman, CfA
N-body simulations are the standard tool for modeling LCDM structure formation but are not without their drawbacks. For one, they are computationally expensive, requiring 10K+ GPU node-hours for large simulations; for another, they are only as accurate as their discrete "macroparticle" representation of dark matter allows. I'll discuss how we are tackling both of these problems with Abacus. Abacus is a N-body simulation code based on an exact decomposition of the near-field and far-field force, making it exceptionally accurate and fast. Using one dual-GPU node, Abacus can solve a supercomputer-sized N-body problem in a fraction of the node-hours of other codes while retaining significantly higher accuracy. I'll show some of the problems that survey collaborations are having with N-body accuracy and methodologies we are developing to address this.