Colloquia & Seminars
Wednesday colloquia & Friday seminarsLocally, the Center hosts a Wednesday colloquium speaker twice a month and a weekly series of more informal Friday lunch seminars, with both internal and external speakers. The Friday lunch seminar is organized by our Fellows. In addition, there are informal activities, including a weekly journal club (Thunch), periodic open group meetings and seminars.

Past Colloquia & Seminars
DateColloquia & Seminars
June 9, 2017
12:00 PM
Friday noon seminar
Julie Dumas, Vanderbilt University
Testing the Caustic Ring Dark Matter Halo Model Against Observations in the Milky Way
June 2, 2017
12:00 PM
Friday noon seminar
Christopher Tunnell, University of Chicago
XENON1T results and how one can make the world's best direct dark matter detector in 5 easy steps
May 31, 2017
3:30 PM
Wednesday colloquium
Chihway Chang, University of Chicago
Mapping the Cosmos with the Dark Energy Survey - sneak peek of the first year weak lensing results
May 26, 2017
12:00 PM
Friday noon seminar
Niharika Sravan, Northwestern University
Single and binary progenitors of 'partially stripped' supernovae
May 24, 2017
3:30 PM
Wednesday colloquium
Camille Avestruz, University of Chicago
Automated Object Classification for Large Scale Future Surveys: A Strong Lensing Example with Machine Learning
May 19, 2017
12:00 PM
Friday noon seminar
Victor Buza, Harvard University
Constraining Inflation Using Present and Future CMB polarization experiments: performance-based forecasts
May 17, 2017
3:30 PM
Wednesday colloquium
Albert Stebbins, Fermilab
Fast Radio Bursts!
May 12, 2017
12:00 PM
Friday noon seminar
Philip Chang, UW-Milwaukee
The Physics and Cosmology of TeV Blazars
May 5, 2017
12:00 PM
Friday noon seminar
Rebekah A Hounsell, University of California Santa Cruz
Simulations of the WFIRST Supernova Survey and Forecasts of Cosmological Constraints
April 28, 2017
12:00 PM
Friday noon seminar
Antonia Hubbard, Northwestern University
Searching for Dark Matter with the Micro-X Sounding Rocket
April 21, 2017
12:00 PM
Friday noon seminar
Michael J Baker, Johannes Gutenberg University Mainz
The Vev Flip-Flop: Dark Matter Decay between Weak Scale Phase Transitions
April 19, 2017
3:30 PM
Wednesday colloquium
J. Richard Bond, Canadian Institute for Theoretical Astrophysics, University of Toronto
Observing, Mapping and Mocking our Cosmic Beginnings
April 14, 2017
12:00 PM
Friday noon seminar
Scott Hertel, University of Massachusetts
Superfluid 4He as a tool for sub-eV particle physics
April 7, 2017
12:00 PM
Friday noon seminar
Cosmin Deaconu, The University of Chicago
Radio-detection of Ultra-High Energy Neutrinos with the ANITA Long-Duration Balloon Payload
April 5, 2017
3:30 PM
Wednesday colloquium
Juan I. Collar, University of Chicago
News from PICO and COHERENT
March 31, 2017
12:00 PM
Friday noon seminar
Alessandro Manzotti, University of Chicago
Delensing CMB B-modes: results from SPT
March 17, 2017
12:00 PM
Friday noon seminar
Amy Lowitz, University of Wisconsin - Madison
Kinetic Inductance Detectors for 100 GHz CMB Polarimetry
March 10, 2017
12:00 PM
Friday noon seminar
David Moore, Yale University
Precision searches for new physics using optically levitated microspheres
March 3, 2017
12:00 PM
Friday noon seminar
Andrew Wetzel, Carnegie Observatories, Caltech, UC Davis
Simulating Milky Way-like Galaxies with Realistic Satellite Populations
February 24, 2017
12:00 PM
Friday noon seminar
Zhong-Zhi Xianyu, Harvard University
Standard Model Background of the Cosmological Collider
February 17, 2017
12:00 PM
Friday noon seminar
Yi-Zen Chu, University of Minnesota Duluth
Cosmological Gravitational Waves: Causal Structure And Memories
February 10, 2017
12:00 PM
Friday noon seminar
Elena Giusarma, Carnegie Mellon University
Testing neutrino properties with cosmological observables
February 3, 2017
12:00 PM
Friday noon seminar
Douglas Applegate, The University of Chicago
Recent Advances & Current Challenges in Cosmology with Galaxy Clusters
January 27, 2017
12:00 PM
Friday noon seminar
Evangelos Sfakianakis, UIUC
From axion inflation to leptons, baryons and cosmological magnetic fields
January 20, 2017
12:00 PM
Friday noon seminar
Jayden Newstead, Arizona State University
Coherent neutrino-nucleus scattering: signal or background?
January 18, 2017
3:30 PM
Wednesday colloquium
Alex Drlica-Wagner, Fermilab
The Milky Way's Dark Companions
December 9, 2016
12:00 PM
Friday noon seminar
Alvaro Chavarria, The University of Chicago
Solid-state imaging detectors for low-energy particle physics
December 7, 2016
3:30 PM
Wednesday colloquium
Wendy Freedman, KICP
Increasing Accuracy and Increasing Tension in H0
November 18, 2016
12:00 PM
Friday noon seminar
Allison Merritt, Yale University
Substantial Variation in the Stellar Halos of Spiral Galaxies
November 11, 2016
12:00 PM
Friday noon seminar
Yuan Li, University of Michigan
Cooling and AGN heating in cool-core galaxy clusters
November 9, 2016
3:30 PM
Wednesday colloquium
Surjeet Rajendran, UC Berkeley
New Directions in Searching for the Dark Universe
November 4, 2016
12:00 PM
Friday noon seminar
Arran Phipps, Stanford University
Dark Matter Radio (Hidden Photons/Axions)
October 28, 2016
12:00 PM
Friday noon seminar
Ian P Stern, University of Florida
ADMX (Axion Dark Matter eXperiment)
October 26, 2016
3:30 PM
Wednesday colloquium
Ben Farr, Enrico Fermi Institute and KICP
The First Four Months of Gravitational Wave Astronomy
October 21, 2016
12:00 PM
Friday noon seminar
Jeffrey P Filippini, University of Illinois, Urbana-Champaign
SPIDER: Exploring the dawn of time from above the clouds
October 14, 2016
12:00 PM
Friday noon seminar
Yuhsin Tsai, University of Maryland
Partially Acoustic Dark Matter, Interacting Dark Radiation, and Large Scale Structure
October 12, 2016
3:00 PM
Wednesday colloquium
Marcelle Soares-Santos, Fermilab
The Dark Energy Survey and Gravitational Waves
October 7, 2016
12:00 PM
Friday noon seminar
Chihway Chang, UofC
Preparing for the 21cm future - lessons from the Bleien Galactic Survey project
September 30, 2016
12:00 PM
Friday noon seminar
Irshad Mohammed, Fermilab
Towards precision cosmology with large scale structures: the halo model and perturbative approaches

Testing the Caustic Ring Dark Matter Halo Model Against Observations in the Milky Way
June 9, 2017 | 12:00 PM | ERC 401 | Friday noon seminar
Friday noon seminar
Julie Dumas, Vanderbilt University

A prediction of axion dark matter models is they can form Bose-Einstein condensates and rigid caustic rings as a halo collapses in the non-linear regime. In this talk, I will present results from the first study of the caustic ring model for the Milky Way halo (Duffy & Sikivie 2008), focusing on observational consequences. I will describe the formalism for calculating the gravitational acceleration of a caustic ring halo. The caustic ring dark matter theory reproduces a roughly logarithmic halo, with large perturbations near the rings. I will show that this halo can reasonably match the known Galactic rotation curve. We explored the effects of dark matter caustic rings on dwarf galaxy tidal disruption with N-body simulations. N-body simulations of the Sagittarius (Sgr) dwarf galaxy in a caustic ring halo potential, with disk and bulge parameters that are tuned to match the Galactic rotation curve, match observations of the Sgr trailing tidal tails as far as 90 kpc from the Galactic center. Like the Navarro-Frenk-White (NFW) halo, they are, however, unable to match the leading tidal tail. None of the caustic, NFW, or triaxial logarithmic halos are able to simultaneously match observations of the leading and trailing arms of the Sagittarius stream. I will further show that simulations of dwarf galaxies that move through caustic rings are qualitatively similar to those moving in a logarithmic halo.

XENON1T results and how one can make the world's best direct dark matter detector in 5 easy steps
June 2, 2017 | 12:00 PM | ERC 576 | Friday noon seminar
Friday noon seminar
Christopher Tunnell, University of Chicago

Within the last month, we on the XENON collaboration published our first results from the XENON1T experiment's 34.2 live day run, which is the first ton-scale detector using this world-leading technology of liquid-xenon time-projection chambers. These results do not make any claims of a dark matter signal but rather further weaken the WIMP hypothesis. In these results, which had a large contribution from the KICP XENON group, you can think of there as being a checklist of requirements needed to have strong results like ours in this competitive field. This includes rather physical requirements such as being able to contain ~3000 kg of liquid xenon at cryogenic temperatures, where I will discuss the hardware insomuch as it is of interest to cosmologists. My focus however will be on the analysis we performed, where beyond our WIMP results, we were able to establish that this detector is the quietest on earth (1.93 +/- 0.25) * 10^-4 events/(kg day keV). This allows us, when combined with novel calibration and analysis techniques, to set the strongest limits for WIMP masses above 10 GeV, with a minimum of 7.7e-47 cm^2 at 35 GeV. In explaining how we produced these results, the promising prospects for XENON1T in the coming years will become clear.

Mapping the Cosmos with the Dark Energy Survey - sneak peek of the first year weak lensing results
May 31, 2017 | 3:30 PM | ERC Auditorium 161 | Wednesday colloquium
Image credit: Andreas Papadopoulos
Wednesday colloquium
Chihway Chang, University of Chicago

Weak gravitational lensing, or weak lensing, is one of the most powerful tools in cosmology. The technique relies on measuring accurately the shape of a large number of galaxies, and statistically translating the shape measurements into (dark matter) mass distributions. The first year data from the Dark Energy Survey (DES Y1) provides the most powerful weak lensing dataset to date. In this talk I will first give an update on the status of the cosmology analysis from DES Y1 data and present some preliminary results. Next, I will describe our work in generating and testing the wide-field weak lensing mass maps from the galaxy shape measurements and some exciting applications for the maps. I will end with thoughts on how weak lensing could also inform us on various topics of galaxy formation, which is essential for completing the story behind the Universe we see today.

Single and binary progenitors of 'partially stripped' supernovae
May 26, 2017 | 12:00 PM | ERC 401 | Friday noon seminar
Friday noon seminar
Niharika Sravan, Northwestern University

The rise of survey telescopes in the past decade have led to an explosion in the number of supernovae (SNe) discovered and the amount of information available on them. They have revealed an unexpected diversity in the properties of progenitor stars and their environments. Unfortunately, theoretical efforts to explain these have lagged. However, there is a growing urgency for robust theoretical models to inform supernova (SN) observations given the imminent launch of LSST, which threatens to overwhelm current techniques for studying SNe.

As a step towards addressing this vacuum, we undertake a comprehensive study of a group of 'partially stripped' SNe, known as Type IIb SNe. These are in need of theoretical interpretation because mechanisms driving significant mass loss in the progenitor stars are an open question. In this talk, I will describe single and binary progenitors of Type IIb SNe and their properties. I will present results for the application of our work to the most recent Type IIb with a detected progenitor, SN 2016gkg. In particular, we derive observational constraints for the progenitors and binary companions of SN 2016gkg that can be verified in the future.

Automated Object Classification for Large Scale Future Surveys: A Strong Lensing Example with Machine Learning
May 24, 2017 | 3:30 PM | ERC 161 | Wednesday colloquium
Wednesday colloquium
Camille Avestruz, University of Chicago

Video
Gravitational lensing offers a direct probe of the underlying mass distribution of lensing systems, a window to the high redshift universe, and a geometric probe of cosmological models. The advent of large scale surveys such as the Large Synoptic Sky Telescope and Euclid has prompted a need for automatic and efficient identification of strong lensing systems. We present (1) (ALL) Automated Lensing Learner, a strong lensing identification pipeline that will be publicly released as open source software, and (2) a publicly available mock LSST dataset with strong galaxy-galaxy lenses. In this first application of the pipeline, we employ a fast feature extraction method, Histogram of Oriented Gradients (HOG), to capture edge patterns that are characteristic of strong gravitational arcs in galaxy-galaxy lensing. We use logistic regression to train a supervised classifier model on the HOG of HST- and LSST-like images. Our tests demonstrate an efficient and effective method for automatically identifying strong lenses that captures much of the complexity of the arc finding problem. The linear classifier both runs on a personal laptop and can easily scale to large data sets on a computing cluster, all while using existing open source tools.

Constraining Inflation Using Present and Future CMB polarization experiments: performance-based forecasts
May 19, 2017 | 12:00 PM | ERC 401 | Friday noon seminar
Friday noon seminar
Victor Buza, Harvard University

A long-sought prediction of our most refined approach to early universe cosmology, the inflationary theory, is the existence of primordial gravitational waves. A potential observational signature of these waves are so called "primordial B-modes" in CMB polarization maps. However, local sources such as galactic dust and synchrotron, as well as lensing of the CMB, also produce "B-mode" signals that need to be untangled from the observed signal in order to make precise claims about the early universe.

In this talk I will describe a multicomponent likelihood analysis framework for joint analyses of various CMB datasets that takes into account multiple signal types, and its subsequent use for analysis of BICEP2, Keck and Planck CMB polarization data to derive the tightest current constraints, parametrized by the tensor-to-scalar ratio, on primordial B-modes (r<0.07).

I will also talk about modifying this likelihood framework into a spectral-based Fisher projection framework that allows using current achieved performances from various CMB experiments to make robust forecasts for future CMB-polarization endeavors. This approach is unique in its implementation of real-life experimental inefficiencies by using actual on-sky performance of BICEP/Keck experiments, which produced leading constraints on r, to scale to future capabilities. This framework allows for rapid iteration on how various experimental configurations affect the underlying science results. It has been extensively used in the context of optimizing survey configurations, and calculating inflation projections for the next generation experiment in the BICEP/Keck series, and the field-wide CMB-Stage 4 endeavor.

Fast Radio Bursts!
May 17, 2017 | 3:30 PM | ERC 161 | Wednesday colloquium
Wednesday colloquium
Albert Stebbins, Fermilab

Video
On a human scale most astronomical sources are large and vary slowly. They must be large enough to produce enough light be to seen at astronomical distances and the light travel time across a large source limits the timescale for observable variations. Nevertheless in recent years extremely rapidly varying radio emission has been detected and found to be a common phenomena. The most extreme case has timescales as small as one nanosecond, inferred size smaller than one meter, peak luminosity exceeding that of the Sun, and is observed at a distance of 2kpc. More numerous and further away are Fast Radio Bursts (FRBs), originating at cosmological distances, lasting a millisecond and arriving at Earth a few times a minute. These events are the brightest sources known in terms of an off-scale brightness temperature, yet the emission mechanism is undetermined. I will discuss some ideas for the origin of this emission and how these bright bursts could be used to augment gravitational wave and neutrino astronomy as well as the study of cosmological parameters and the intergalactic medium.

The Physics and Cosmology of TeV Blazars
May 12, 2017 | 12:00 PM | ERC 401 | Friday noon seminar
Friday noon seminar
Philip Chang, UW-Milwaukee

The universe is teeming with very high energy gamma ray sources (> 100 GeV), but it is generally thought that their impact on the universe is minor at best. On energetic grounds, this assumption seems well-founded because the energy density in TeV photons is 0.2% of that of ionizing photons from quasars. However, as I hope to show in this talk, this is not the case. Rather, the greater efficiency by which TeV photons can be converted to heating in the intergalactic medium (IGM) allows TeV blazars dominate the heating of the IGM at low redshift. I will discuss the nature of this conversion via beam instabilities. I will then discuss how the resultant heating from these TeV sources makes dramatic differences for constraints on the intergalactic magnetic field, on the formation of structure, and on the redshift evolution of TeV blazars. I will also discuss how it gives rise to the inverted temperature-density profile of the IGM, the bimodality of galaxy clusters, and the paucity of dwarf galaxies in galactic halos and voids.

Simulations of the WFIRST Supernova Survey and Forecasts of Cosmological Constraints
May 5, 2017 | 12:00 PM | ERC 401 | Friday noon seminar
Friday noon seminar
Rebekah A Hounsell, University of California Santa Cruz

The Wide Field InfraRed Survey Telescope (WFIRST) was the highest ranked large space-based mission of the 2010 New Worlds, New Horizons decadal survey. It is now a NASA mission in formulation with a planned launch in the mid-2020's. A primary mission objective is to precisely constrain the nature of dark energy through multiple probes, including Type Ia supernovae (SNe Ia). Within this talk I present the first realistic simulations of the WFIRST SN survey based on current hardware specifications and using open-source tools. I will review different survey strategies with varying time allocations between WFIRST's wide-field channel (WFC) imager and integral field channel (IFC) spectrometer, and predict the dark energy task force figure of merit (DETF FoM) for each strategy. Even without improvements to other cosmological probes, the WFIRST SN survey has the potential to increase the FoM by more than an order of magnitude from the current values.

Searching for Dark Matter with the Micro-X Sounding Rocket
April 28, 2017 | 12:00 PM | ERC 401 | Friday noon seminar
Friday noon seminar
Antonia Hubbard, Northwestern University

The Micro-X sounding rocket uses a Transition Edge Sensor (TES) array to make X-ray observations. The improved energy resolution of TESs compared to traditional space-based X-ray detectors brings new precision to both supernova remnant observations and the X-ray search for sterile neutrino dark matter. Current X-ray observations disagree over the potential presence of a 3.5 keV X-ray line consistent with a sterile neutrino interaction, and Micro-X is in a unique position to establish or refute the presence of this line. I will present the construction status of the instrument and expectations for flight observations, with special emphasis given to the prospects of sterile neutrino studies.

The Vev Flip-Flop: Dark Matter Decay between Weak Scale Phase Transitions
April 21, 2017 | 12:00 PM | ERC 401 | Friday noon seminar
Friday noon seminar
Michael J Baker, Johannes Gutenberg University Mainz

We discuss a new alternative to the Weakly Interacting Massive Particle (WIMP) paradigm for dark matter. Rather than being determined by thermal freeze-out, the dark matter abundance in this scenario is set by dark matter decay, which is allowed for a limited amount of time just before the electroweak phase transition. We discuss a concrete model which exhibits a ``vev flip-flop'' and show that it is phenomenologically successful in the most interesting regions of its parameter space. We comment on detection prospects, primarily at the LHC.

Observing, Mapping and Mocking our Cosmic Beginnings
April 19, 2017 | 3:30 PM | ERC 161 | Wednesday colloquium
Wednesday colloquium
J. Richard Bond, Canadian Institute for Theoretical Astrophysics, University of Toronto

Video
I will give my take on the phenomenology (and yes theory) of inflation as revealed in Planck and other CMB) and LSS experiments, but with an eye to the glorious CMB future of AdvACT, CCAT-p, Simons Observatory, Stage 4, and the LSS of Euclid, Chime, and much more besides that we mock. Apart from displaying linear and quadratic maps of the primordial universe, a compression of what we now know, i will chat about CMB/LSS anomalies, in practice and in theory, pointing to post-inflation chaotic dynamical systems that can lead to subdominant non-Gaussian signals unlike the ones we have put such stringent constraints on with Planck 2015; and relate everything to non-equilibrium entropies, including the formation of all cosmic structure.

Superfluid 4He as a tool for sub-eV particle physics
April 14, 2017 | 12:00 PM | ERC 401 | Friday noon seminar
Friday noon seminar
Scott Hertel, University of Massachusetts

Efforts to observe interactions between galactic dark matter and laboratory test particles are undergoing a transition, broadening out from the standard WIMP hypothesis. Some models newly attracting attention inhabit the keV-MeV mass range. The dominant practical challenge in probing this light mass range is the development of detector technologies sensitive to sub-eV energy depositions. I'll describe both the general challenge of this low-energy regime and also one possible technological path forward, employing meV-scale kinetic excitations of the superfluid state.

Radio-detection of Ultra-High Energy Neutrinos with the ANITA Long-Duration Balloon Payload
April 7, 2017 | 12:00 PM | ERC 401 | Friday noon seminar
Friday noon seminar
Cosmin Deaconu, The University of Chicago

The interactions of ultra-high-energy cosmic rays with the Cosmic Microwave Background are expected to produce a flux of EeV-scale neutrinos through the GZK process. Successful detection of these cosmogenic neutrinos would help elucidate the sources of the highest-energy cosmic rays and probe the standard model in a new regime. Due to the low predicted flux and small interaction cross-section, an enormous detector is required for successful measurement.

The Antarctic Impulse Transient Antenna (ANITA) long-duration balloon payload scans the Antarctic ice sheet for radio emission produced by the interactions of cosmogenic neutrinos in ice. At altitude, ANITA instantaneously instruments a volume on the order of 10^6 km^3. This talk will provide an overview of the ANITA detection technique, instrumentation, analysis methods, and results so far. I will focus on the recent fourth flight of ANITA, completed in December, as well as a strange event detected in the first ANITA flight that is potentially of neutrino origin.

News from PICO and COHERENT
April 5, 2017 | 3:30 PM | ERC 401 | Wednesday colloquium
Wednesday colloquium
Juan I. Collar, University of Chicago

Video
I will discuss the most recent results from PICO, a search for WIMP dark matter using bubble chambers, as well as future plans and some exciting lines of related research. I will then move on to cover COHERENT, an ongoing effort at ORNL's Spallation Neutron Source to detect and exploit coherent neutrino-nucleus scattering, soon to produce first results. The "glue" between these two subjects will be an elaboration on the overlap in techniques and methods used in modern neutrino and astroparticle physics. Abundant examples of this cross-talk will be provided.

Delensing CMB B-modes: results from SPT
March 31, 2017 | 12:00 PM | ERC 401 | Friday noon seminar
Friday noon seminar
Alessandro Manzotti, University of Chicago

A promising signature of cosmic inflation is the presence of a "B-mode" component in the polarization of the Cosmic Microwave Background (CMB) induced by primordial gravitational waves. For many inflation models, this B-mode signal is predicted to be at a level detectable in the near future. However current searches are limited by a "lensing B-mode" component that is produced by gravitationally lensing primordial E modes. In order to potentially detect the inflationary signal from B-mode measurements, lensing B modes must be characterized and removed in a process referred to as "delensing." This process has been studied extensively theoretically and with simulations, but has not been performed on polarization data. In this talk, I will present a demonstration of CMB B-mode delensing using polarization data from the South Pole Telescope polarimeter, SPTpol. Furthermore, using realistic simulations that include filtering and realistic CMB noise, we will show what is currently limiting the delensing efficiency and how it will rapidly improve in the near future.

Kinetic Inductance Detectors for 100 GHz CMB Polarimetry
March 17, 2017 | 12:00 PM | ERC 401 | Friday noon seminar
Friday noon seminar
Amy Lowitz, University of Wisconsin - Madison

Kinetic inductance detectors (KIDs) are a promising detector technology across a broad range of wavelengths from mm-waves up to the soft X-ray regime. KIDs offer relatively simple, relatively inexpensive fabrication and straightforward passive frequency-domain multiplexing, which makes them an attractive solution for instruments requiring very high pixel-count arrays, including upcoming CMB polarimetry instruments. In this talk, I will describe a recent effort to produce a prototype array of direct-absorbing lumped element KIDs designed for CMB polarimetry at 100 GHz (3 mm) with the QUBIC telescope, including a discussion of design considerations, material development, and measured array performance.

Precision searches for new physics using optically levitated microspheres
March 10, 2017 | 12:00 PM | ERC 401 | Friday noon seminar
Friday noon seminar
David Moore, Yale University

I will describe the development of a new class of force sensors based on optically levitated dielectric microspheres in high vacuum, which allow the detection of sub-attonewton forces acting on micron sized objects. These force sensors can enable novel precision searches for new physics through the detection of weakly coupled or short range (<< 1 mm) interactions. Results from the initial application of these force sensors to search for millicharged dark matter particles bound in matter, and for interactions arising in certain screened scalar dark energy models, will be presented. Finally, I will discuss the expected sensitivity of these techniques to search for non-Newtonian or non-Coulombic forces at micron length scales, which can probe a variety of models of physics beyond the Standard Model.

Simulating Milky Way-like Galaxies with Realistic Satellite Populations
March 3, 2017 | 12:00 PM | ERC 401 | Friday noon seminar
Friday noon seminar
Andrew Wetzel, Carnegie Observatories, Caltech, UC Davis

Low-mass 'dwarf' galaxies trace structure formation on the smallest cosmological scales and represent the most significant challenges to the cold dark matter (CDM) model. I will introduce the Latte simulations, a new suite of cosmological zoom-in baryonic simulations that model the formation of Milky Way-like galaxies at parsec-scale resolution, using the FIRE (Feedback in Realistic Environments) model for star formation and feedback. Using these simulations, I will discuss the roles of cosmic accretion and stellar feedback in driving the formation and structure of disk galaxies like the Milky Way. These simulations also self-consistently resolve the satellite dwarf galaxies that form around each host. I will discuss the impact of stellar feedback and MW-like environments on dark-matter subhalos and their connection to dwarf galaxies, demonstrating progress in addressing the 'missing satellites' and 'too-big-to-fail' problems of LCDM cosmology.

Standard Model Background of the Cosmological Collider
February 24, 2017 | 12:00 PM | ERC 401 | Friday noon seminar
Friday noon seminar
Zhong-Zhi Xianyu, Harvard University

Primordial non-Gaussianities record interactions of fields in the early universe, which can be viewed as collision events in a "Cosmological Collider" with huge energy. In this talk, I shall introduce the workings of the Cosmological Collider as an explorer of new physics at very high scales, and describe the Standard Model spectrum during inflation and its "background signals" in Cosmological Collider. The nontrivial quantum correction during inflation plays a crucial role in this process, which I shall describe in detail.

Cosmological Gravitational Waves: Causal Structure And Memories
February 17, 2017 | 12:00 PM | ERC 401 | Friday noon seminar
Friday noon seminar
Yi-Zen Chu, University of Minnesota Duluth

Despite being associated with particles of zero rest mass, electromagnetic and gravitational waves do not travel solely on the null cone in generic curved spacetimes. (That is, light does not always propagate on the light cone.) This inside-the-null-cone propagation of waves is known as the tail effect, and finding novel ways of understanding it in the strong field regime near a black hole may find applications for modeling the gravitational signals sought after by next-generation space-based detectors such as LISA.

Motivated by these considerations -- and as a first step -- I have been exploring techniques to understand the causal structure of scalar, electromagnetic and gravitational waves in cosmological spacetimes. I will describe my efforts to date, which include how the gravitational wave memory effects in 4D asymptotically flat spacetime generalize to the cosmological case.

Testing neutrino properties with cosmological observables
February 10, 2017 | 12:00 PM | ERC 401 | Friday noon seminar
Friday noon seminar
Elena Giusarma, Carnegie Mellon University

One of the great puzzles related to the ΛCDM model is the nature of the dark matter (DM) component. In standard cosmology, hot, thermal relics are identified with the three light, active neutrinos which are sub-eV elementary particles which, apart from gravity, only interact via weak interactions. From neutrino oscillation experiments we know that neutrinos have masses but they are not sensitive to the absolute neutrino mass scale. Cosmology provides an independent tool to tackle the absolute scale of neutrino and to study its properties. In this talk I will illustrate the implications of neutrino properties on cosmological observables, in particular on the Cosmic Microwave Background radiation and on Large Scale Structure, and I will explore the current constraints on neutrino masses focusing also on the dependence of the cosmological limits on the total neutrino mass under the assumption of different mass spectra.

Recent Advances & Current Challenges in Cosmology with Galaxy Clusters
February 3, 2017 | 12:00 PM | ERC 401 | Friday noon seminar
Friday noon seminar
Douglas Applegate, The University of Chicago

Observations of galaxy clusters not only test the basic parameters of the Lambda-CDM universe, but also test new physics such as non-zero neutrino masses, evolving dark energy, and departures from General Relativity on large scales. In this talk, I will first motivate why clusters are so useful for cosmology and why we are confident that these measurements are robust. In particular, I will describe how gravitational lensing measurements have been essential to cosmological constraints with the Weighing the Giants project, which reported a 12% constraint on Omega_m and a 15% constraint on a constant dark energy equation of state (when assuming flatness) from cluster data alone. While currently competitive, control of systematic uncertainties in weak lensing measurements need to improve by an order of magnitude to fully realize the potential of cluster cosmology with Stage-IV dark energy experiments that are turning on in the coming decade. I will detail some of the ongoing work within the South Pole Telescope and Dark Energy Science collaborations that is moving us towards the 1% systematics level, and highlight some of the interesting challenges yet to be solved.

From axion inflation to leptons, baryons and cosmological magnetic fields
January 27, 2017 | 12:00 PM | ERC 401 | Friday noon seminar
Friday noon seminar
Evangelos Sfakianakis, UIUC

Axions are attractive candidates for theories of large-field inflation that are capable of generating observable primordial gravitational wave backgrounds. These fields enjoy shift-symmetries that protect their role as inflatons from being spoiled by coupling to unknown UV physics. This symmetry also restricts the couplings of these axion fields to other matter fields. At lowest order, the only allowed interactions are derivative couplings to gauge fields and fermions. These derivative couplings lead to the biased production of fermion and gauge-boson helicity states during and after inflation. I will describe some recent work on preheating in axion-inflation models that are derivatively coupled to Abelian gauge-fields and fermion axial-currents.
For an axion coupled to U(1) gauge fields it was found that preheating is efficient for a wide range of parameters. In certain cases the inflaton is seen to transfer all its energy to the gauge fields within a few oscillations. Identifying the gauge field as the hypercharge sector of the Standard Model can lead to the generation of cosmologically relevant magnetic fields.
Coupling the inflaton-axion to Majorana fermions leads to the biased production of fermion helicity-states which can have interesting phenomenological implications for leptogenesis.

Coherent neutrino-nucleus scattering: signal or background?
January 20, 2017 | 12:00 PM | ERC 401 | Friday noon seminar
Friday noon seminar
Jayden Newstead, Arizona State University

The next generation of dark matter direct detection experiments will be sensitive to coherent nuclear scattering of solar neutrinos. This presents an irreducible background to dark matter searches, the so called 'neutrino floor'. However, this effect that has yet to be observed and so provides an opportunity for discovery. Dedicated experiments are racing to observe this effect and use it as a probe of new physics. In this talk I will discuss the neutrino floor and present some dark matter models where the prospects for discovery are not so grim. Then I will introduce the MINER experiment, a Texas A&M effort to observe coherent neutrino-nucleus scattering, and present its sensitivity to models of new physics.

The Milky Way's Dark Companions
January 18, 2017 | 3:30 PM | ERC 161 | Wednesday colloquium
Wednesday colloquium
Alex Drlica-Wagner, Fermilab

PDF | Video
Our Milky Way galaxy is surrounded by a host of small, dark-matter-dominated satellite galaxies. Over the past two years, the Dark Energy Camera (DECam) has nearly doubled the number of known Milky Way satellite galaxies compared to the previous 80 years combined. While these discoveries continue to help resolve the "missing satellites problem", they have also raised new questions about the influence of the Magellanic Clouds on the Milky Way's satellite population. In the near future, the rapidly growing population of dwarf galaxies will be sensitive to deviations from ΛCDM at small scales, while definitively testing whether the annihilation of dark matter particles could be responsible for excess gamma-ray emission from the Galactic center. I will summarize recent results, outstanding questions, and upcoming advancements in the study of the Milky Way's dark companions.

Solid-state imaging detectors for low-energy particle physics
December 9, 2016 | 12:00 PM | ERC 401 | Friday noon seminar
Friday noon seminar
Alvaro Chavarria, The University of Chicago

The low noise, high spatial resolution and reliable performance of charge-coupled devices (CCDs) and complementary metal-oxide-semiconductor (CMOS) active pixel arrays have made them detectors of choice for digital imaging, from consumer electronics to state-of-the-art astronomical cameras. Although the slow time response of these devices has limited their application in high-energy particle physics, for the case of rare-event searches, where the particle interaction rate is extremely low, their properties can be fully exploited to build detectors that outperform in many aspects the traditional technologies of the field. I will present recent results from the DAMIC experiment, a low-mass dark matter search consisting of low-noise CCDs deployed in the SNOLAB laboratory. I will show how the exquisite spatial resolution of the detector allows for particle identification, and provides the unique capability to reject sequences of radioactive decay with utmost efficiency. These techniques can be extended to the field of neutrinoless double beta decay. I will present a recent proposal where we argue that a large array of amorphous Se-82 imagers based on CMOS technology could achieve the background requirements necessary to test if neutrinos are Majorana fermions even in the case of a normal hierarchy of neutrino masses.

Increasing Accuracy and Increasing Tension in H0
December 7, 2016 | 3:30 PM | ERC 161 | Wednesday colloquium
Wednesday colloquium
Wendy Freedman, KICP

PDF | Video
The accuracy in direct measurement of distances to galaxies has continued to improve dramatically over the past decade. Local measurements of the Hubble constant based on Hubble Space Telescope observations of astrophysical standard candles -- Cepheids and Type Ia supernovae -- have converged on a value of about 73 km/sec/Mpc with an uncertainty of 2-3%. At the same time, estimates assuming a Lambda-CDM standard model and fitting highly precise measurements of cosmic microwave background fluctuations have yielded a value of Ho = 67 km/sec/Mpc. The two methods disagree at approximately the 3-sigma level. The reason for this discrepancy is not understood at present, and new data have only increased the tension. If real, the disagreement could be signaling missing physics in the standard model; for example, additional dark radiation. Major efforts are ongoing to improve further the accuracy in the local measurements, including developing other techniques to test the Cepheid distance scale. In the near future JWST and Gaia will provide a path to measuring Ho to 1%, comparable to the precision in CMB measurements.

Substantial Variation in the Stellar Halos of Spiral Galaxies
November 18, 2016 | 12:00 PM | ERC 401 | Friday noon seminar
Friday noon seminar
Allison Merritt, Yale University

The Dragonfly Telephoto Array, comprised of 48 individual Canon telephoto lenses operating together as a single telescope, is an innovative approach to low surface brightness imaging. Sub-nanometer coatings on each optical element reduce scattered light from nearby bright stars and compact galaxy centers -- typically a key obstacle for integrated light observations -- by an order of magnitude, and Dragonfly's large field of view (2 x 2.6 degrees for a single frame) provides a large-scale view of galactic stellar halos and satellite systems. Using extremely deep (>30 mag/arcsec^2) optical imaging in g and r bands from the Dragonfly Nearby Galaxies Survey (DNGS), we have characterized the stellar halos of a sample of nearby luminous galaxies. I will present measurements of the stellar halo mass fractions of an initial sample of spiral galaxies from the survey, and discuss these in the context of the assembly histories of individual galaxies.

Cooling and AGN heating in cool-core galaxy clusters
November 11, 2016 | 12:00 PM | ERC 401 | Friday noon seminar
Friday noon seminar
Yuan Li, University of Michigan

The feedback from active galactic nuclei (AGNs) is widely considered to be the major heating source in cool-core galaxy clusters, preventing a classical cooling flow where the intra-cluster medium (ICM) cools at hundreds to a thousand solar masses per year. We perform adaptive mesh simulations using Enzo including both momentum-driven AGN feedback and star formation to study the interplay between ICM cooling, AGN heating and star formation over 6.5 Gyr in an isolated cool-core cluster. We find that AGN jets globally heat up the ICM via weak shock waves and turbulence. Locally, cold clumps can cool out of the ICM due to the non-linear perturbation driven by the AGN jets. These cold clumps feed both star formation and the supermassive black hole (SMBH), triggering an AGN outburst which increases the entropy of the ICM and reduces its cooling rate. When star formation completely consumes the cold gas, leading to a brief shutoff of the AGN, the ICM quickly cools and develops multiphase gas again, followed by another cycle of star formation/AGN outburst. The simulation reproduces a wide range of observed properties and naturally explain the variety of star forming clouds observed in the center of cool-core clusters.

New Directions in Searching for the Dark Universe
November 9, 2016 | 3:30 PM | ERC 161 | Wednesday colloquium
Wednesday colloquium
Surjeet Rajendran, UC Berkeley

PDF | Video
Observational bounds currently permit the existence of a large number of dark matter candidates, ranging from ultra-light axions with masses ~ 10^(-22) eV to MACHOs with mass as large as 10^(24) gm. It is important to develop experimental methods to constrain this vast range of parameters. In this talk, I will describe new experimental methods to probe a wide variety of dark matter candidates, ranging from ultra-light axions with masses ~ 10^(-22) eV to light WIMPs with mass in the keV - GeV range. A variety of precision measurement technologies such as optical/atomic interferometry and SQUID magnetometry can be applied to search for these particles. I will also discuss methods to search for the direction of the nuclear recoil induced by conventional WIMP scattering in detectors with solid state densities. These directional detectors may enable probes of conventional WIMP dark matter beyond the solar neutrino floor.

Dark Matter Radio (Hidden Photons/Axions)
November 4, 2016 | 12:00 PM | ERC 401 | Friday noon seminar
Friday noon seminar
Arran Phipps, Stanford University

Determining the composition of dark matter is at the forefront of modern scientific research. There is compelling evidence for the existence of vast quantities of dark matter throughout the universe, however it has so-far eluded all direct detection efforts and its identity remains a mystery. While weakly interacting massive particles (WIMPs) are a favored candidate and have been the primary focus of direct detection for several decades, there has been recent interest in searching for ultra light field dark matter. The Dark Matter Radio is a tunable superconducting high-Q lumped-element resonator (read out with SQUIDs) being built to search for sub-eV hidden photon and axion dark matter. I will discuss the motivation, detection strategy, design, and current status of the DM Radio experiment.

ADMX (Axion Dark Matter eXperiment)
October 28, 2016 | 12:00 PM | ERC 401 | Friday noon seminar
Friday noon seminar
Ian P Stern, University of Florida

Nearly all astrophysical and cosmological data point convincingly to a large component of cold dark matter (CDM) in the Universe. The axion particle, first theorized as a solution to the strong charge-parity problem of quantum chromodynamics, has been established as a prominent CDM candidate. Cosmic observation and particle physics experiments have bracketed the unknown mass of CDM axions between approximately a μeV and a meV.

The Axion Dark Matter eXperiment (ADMX) is a direct-detection CDM axion search which has set limits at the KSVZ coupling of the axion to two photons for axion masses between 1.9 and 3.7 μeV. ADMX has recently begun conducting searches with an upgraded detector, which will allow for detection at even the most pessimistic couplings within this mass range. In order to expand the mass reach of the detector, ADMX is conducting extensive research and development of microwave cavity technology. Status of the experiment, current research, and projected sensitivities will be presented.

The First Four Months of Gravitational Wave Astronomy
October 26, 2016 | 3:30 PM | ERC 161 | Wednesday colloquium
Wednesday colloquium
Ben Farr, Enrico Fermi Institute and KICP

PDF | Video
On September 14, 2015 LIGO made the first direct detection of gravitational waves, marking the beginning of gravitational wave astronomy. The LIGO instruments continued to take data over the next four months, completing their first observing run on January 19, 2016 with 51.5 days of coincident data. I will present results from advanced LIGO's first four months of operation, and what they have taught us thus far.

SPIDER: Exploring the dawn of time from above the clouds
October 21, 2016 | 12:00 PM | ERC 401 | Friday noon seminar
Friday noon seminar
Jeffrey P Filippini, University of Illinois, Urbana-Champaign

Inflation is thought to have seeded the cosmos with a hum of primordial gravitational waves - unique messengers from the universe's earliest moments. These ripples in spacetime should have left a unique "B-mode" signature on the polarization of the cosmic microwave background. SPIDER is a powerful balloon-borne instrument designed to tease out this polarization pattern in the presence of galactic foregrounds. I will give an update from SPIDER's successful long-duration balloon flight over the Antarctic ice in January 2015, including performance estimates and the current status of the analysis, as well as a status report on payload development for SPIDER's upcoming second flight.

Partially Acoustic Dark Matter, Interacting Dark Radiation, and Large Scale Structure
October 14, 2016 | 12:00 PM | ERC 401 | Friday noon seminar
Friday noon seminar
Yuhsin Tsai, University of Maryland

The standard paradigm of collisionless cold dark matter is in tension with measurements on large scales. In particular, the best fit values of the Hubble rate and the matter density perturbation inferred from the CMB seem inconsistent with the results from direct measurements. In this talk, I will discuss these issues and propose a solution to both problems from a dark sector that contains dark acoustic oscillations with dark fluid. Such a solution can be tested by future experiments designed to probe the CMB and large scale structure.

The Dark Energy Survey and Gravitational Waves
October 12, 2016 | 3:00 PM | ERC 161 | Wednesday colloquium
Wednesday colloquium
Marcelle Soares-Santos, Fermilab

PDF | Video
In this talk I present recent results of the Dark Energy Survey (DES) searches for optical counterparts to Gravitational Wave (GW) events detected by the LIGO/Virgo Collaboration. Our program achieved greater sensitivity than any other optical facility last year. For the second observing campaign (Fall/2016-Spring/2017) our goals are to either make a detection or establish significant constraints on optical emission from such events. DES is the greatest optical imaging survey yet, aiming at percent-level precision measurements of cosmological parameters from a combination of probes such as type Ia supernovae, galaxy clusters, and weak gravitational lensing. These probes are limited by astrophysical systematics and new independent methods are required in order to beat systematic effects down to sub-percent levels. Standard sirens, events for which distances are determined from their gravitational wave signal, are one possible new method to meet that challenge. Our program will potentially have a great impact in our field by exploring this possibility from the observational perspective. In this talk I will also briefly discuss this exciting prospect for future observing campaigns.

Preparing for the 21cm future - lessons from the Bleien Galactic Survey project
October 7, 2016 | 12:00 PM | ERC 401 | Friday noon seminar
Friday noon seminar
Chihway Chang, UofC

HI intensity mapping is emerging as a new and promising cosmological probe for both the large-scale structure and the early Universe. In preparation for the many large radio projects that are coming online, we launched the Bleien Galactic Survey project as an exercise to test new (and fun) techniques that could develop into useful tools in future surveys. I will first introduce the background science and basic setup of the experiment, and then touch upon two particularly interesting ideas - calibrating the telescope beam using drones, and RFI mitigation with start-of-the-art deep learning algorithms.

Towards precision cosmology with large scale structures: the halo model and perturbative approaches
September 30, 2016 | 12:00 PM | ERC 401 | Friday noon seminar
Friday noon seminar
Irshad Mohammed, Fermilab

The theoretical modeling of the statistical observables of the large-scale structures of the Universe, like galaxy clustering, weak lensing etc., is necessary in order to derive any constraints on the cosmological parameters. One of the most important ingredients of the theoretical model is the two-point correlation function, or its Fourier transform the matter power spectrum. I will discuss the precision in its calculations based on a modified halo model, and the systematic effects due to the baryonic processes. Further, I will also discuss the covariance matrix of the matter power spectrum and its estimators based on the halo model and the perturbation theory. We find the agreement with the simulations is at a 10% level up to k ∼ 1 h/Mpc. We show that all the connected components are dominated by the large-scale modes (k < 0.1h/Mpc), regardless of the value of the wavevectors of the covariance matrix. Finally, I will provide a prescription for how to evaluate the covariance matrix from small box simulations without the need to simulate large volumes.