Physics and Astronomy Calendar

Week of Monday, April 15th 2019


Monday, April 15th 2019
12:15 pm:
Speaker: Keith Bechtol, University of Wisconsin - Madison
Subject: Dark Matter Science in the LSST Era

Astrophysical observations probe the physics of dark matter through its impact on structure formation throughout cosmic history. On large scales, current observational data are well described by a simple model of stable, non-relativistic, collisionless, cold dark matter (CDM). However, many viable theoretical models of dark matter predict deviations from CDM that are testable with current and future observations. Fundamental properties of dark matter — e.g., particle mass, self-interaction cross section, coupling to the Standard Model, and time evolution — can imprint themselves on the macroscopic distribution of matter in a detectable manner. With supporting theoretical efforts and follow-up observations, LSST will be sensitive to several distinct classes of dark matter models, including particle dark matter, field dark matter, and compact objects. I will discuss several astrophysical probes of dark matter microphysics that can be pursued with LSST, as well as synergies between LSST and other astronomical, cosmological, and particle physics experiments of the 2020s.


Tuesday, April 16th 2019
11:15 am:
Speaker: Joe Redish, University of Maryland, College Park
Subject:  Learning Each Other's Ropes: Negotiating interdisciplinary authenticity
Please note the date, time and room change of this seminar for this week only.

Very few students who take introductory physics are physics majors.
They major in Engineering, Biology, Chemistry, Mathematics, or
Architecture to name a few of the many disciplines represented in the
introductory physics class. All of these students are required to
take physics which is viewed by the faculty of those disciplines as
useful, an outlook often not shared by their students. This seminar
will discuss the communication difficulty between physics and other
STEM fields that impacts any attempt to redesign introductory physics
courses that build closer links to students’ major fields. My recent
experience has been in building a physics course for Biology majors.
In doing so, I have been engaged in a multiyear conversation with a
biologist interested in including more physics in his biology course.
These extended discussions have led us both to a deeper understanding
of each other's discipline and to significant changes in the way we
each think about and present our classes.

Faculty Host: Kenneth Heller
1:25 pm:
Space Physics Seminar in 5th floor Walter Library
Subject: MSI Poster session Physical Sciences 2:15-3
Speaker: Andrew Zolli, Vice President, Global Impact Initiatives, Planet
Subject: Using Space to Help Life on Earth: How the Small Satellite Revolution and AI are Transforming How We See and Understand Our World
PLEASE NOTE THE SEMINAR FOR THIS WEEK IS CANCELLED.

A revolution in low-cost, space-based remote sensing, combined with new analytical tools in machine learning, computer vision and artificial intelligence, are creating unprecedented new opportunities for tackling the world’s toughest challenges.

Andrew Zolli is the Vice President for Global Impact Initiatives at Planet (www.planet.com). Started by three NASA engineers, Planet has deployed the largest constellation of Earth-observation satellite in history. Together, these satellites image the entire surface of the Planet, every day, in high resolution. The resulting data holds transformational potential for basic science, and for a host of global challenges, including monitoring deforestation, agriculture and cities, tracking migration, mitigating the effects of climate change, speeding disaster response, and delivering planetary health, among others.

In this talk, Andrew will share lessons from the forefront of the New Space renaissance, as well as breakthrough new remote sensing applications being used right now around the world, and describe how new agile manufacturing and development technologies are accelerating the pace of innovation.

Faculty Host: Vuk Mandic

Wednesday, April 17th 2019
1:25 pm:
Speaker: Jorn Venderbos, University of Pennsylvania
Subject: Many-body band inversions

Topological materials are a new class of quantum materials with remarkable properties, which are rooted in the topology of the ground state wave function. Our understanding of topological electronic phases, in particular free fermion phases, relies on one of the central paradigms of modern electron band theory: the notion of a band inversion. In this talk I will first review what a band inversion is, and then describe our attempt to construct a many-body generalization of the band inversion transition, providing a new perspective for interacting topological phases. In particular, I will introduce a special class of band inversions in two dimensions for which interactions are expected to determine the fate of the transition and present evidence that these provide promising venues for a strongly correlated fractionalized fluid of electrons and holes. I will describe possible routes to material realizations and will discuss connections to new types of topological semimetals in three dimensions as well as superconductors.

Faculty Host: Rafael Fernandes

Thursday, April 18th 2019
10:10 am:
Biophysics Seminar in 120 PAN
Speaker: Erin Sheets, Associate Professor, University of Minnesota, Duluth, Department of Chemistry and Biochemistry
PLEASE NOTE THAT THE SEMINAR FOR THIS WEEK IS CANCELLED
Faculty Host: Elias Puchner
12:10 pm:
Speaker: Mike Makmur and Vihang Mehta
3:35 pm:
Physics and Astronomy Colloquium in Physics Tate B50
Speaker: Ian Tregillis, Los Alamos National Laboratory
Subject: Verification & Validation of a Richtmyer-Meshkov Instability Based Ejecta Source Model, or, Why Should Los Alamos Care About a Freshman Physics Problem?

Computational physicists are commonly faced with the task of resolving discrepancies between the predictions of a complex, integrated multi-physics numerical simulation and corresponding experimental datasets. Such efforts commonly require a slow iterative procedure. However, a different approach is available in cases where the multi-physics system of interest admits closed-form analytic solutions. In this situation, the ambiguity is broken into separate consideration of theory-simulation comparisons (issues of verification) and theory-data comparisons (issues of validation). We demonstrate this with the specific example of a fluid- instability based ejecta source model (“RMI+SSVD”) under development at Los Alamos National Laboratory and implemented in FLAG, a Los Alamos continuum mechanics code. For a specific (but wide-ranging) class of explosively driven metal coupon experiments, the ejecta model prediction inherently reduces to a one-dimensional vacuum kinematics problem. This enables us to compute, purely analytically, piezoelectric ejecta mass measurements suitable for “apples-to-apples” comparisons to both simulated and measured datasets. Thus, studying the solution to a very simple yet overlooked problem yields rich and concrete insights into performance of the model, its strengths and shortcomings, as well as strategies for improving it. These conclusions are made quantitative through the introduction of a straightforward yet rigorous “compatibility score” metric incorporating published measurement uncertainties on relevant experimental parameters.

Faculty Host: Thomas W. Jones

Friday, April 19th 2019
11:00 am:
Nuclear Physics Seminar in Tate 301-20
To be announced.
11:00 am:
Speaker: Ritika Dusad, Cornell University
Subject: Magnetic Monopole Noise

Magnetic monopoles are hypothetical elementary particles exhibiting quantized magnetic charge m_0=±(h⁄(μ_0 e)) and quantized magnetic flux ϕ_0=±h/e. A classic proposal for detecting such magnetic charges is to measure the quantized jump in magnetic flux Φ threading the loop of a superconducting quantum interference device (SQUID) when a monopole passes through it. Naturally, with the theoretical discovery that a plasma containing equal numbers of emergent magnetic charges 〖±m〗_ should exist in several lanthanide-pyrochlore magnetic insulators including Dy_2Ti_2O_7, this SQUID technique was proposed for their direct detection. Experimentally, this has proven extremely challenging because of the high number density, and the generation-recombination (GR) fluctuations, of the monopole plasma. Recently, however, theoretical advances have allowed the¬ spectral density of spontaneously generated magnetic-flux noise S_Φ (ω,T) due to a thermally generated plasma of magnetic monopoles 〖±m〗_to be predicted for Dy2Ti2O7. I will describe development of a high-sensitivity, SQUID based flux-noise spectrometer, and consequent measurements of the frequency and temperature dependence of S_Φ (ω,T) for Dy2Ti2O7 samples. Virtually all the elements of S_Φ (ω,T) predicted for a magnetic monopole plasma, including the existence of intense magnetization noise and its characteristic frequency and temperature dependence, are detected directly. Moreover, measured correlation functions C_Φ (t) of the magnetic-flux noise Φ(t) reveal that the motion of magnetic charges is correlated. A final striking observation is that, since the GR time constants τ(T) are in the millisecond range for Dy2Ti2O7, magnetic monopole flux noise amplified by the SQUID is audible to human perception.

Faculty Host: Vlad Pribiag
12:20 pm:
Speaker: Dan Phan
Subject: Modification of Tc in Low Carrier Density Superconductors
12:30 pm:
Speaker: Matt Reece (Harvard U.)
Subject: The Weak Gravity Conjecture and Photon Masses

I will review the Weak Gravity Conjecture (WGC) and related ideas (such as the Swampland Distance Conjecture and “tower” versions of the WGC), which aim at characterizing generic properties of quantum gravity theories that can be used to diagnose when a low-energy effective field theory cannot be completed into a consistent gravitational theory. As one application, I will explain how arguments based on these conjectures suggest that a theory of quantum gravity requires the photon to be exactly massless.

2:30 pm:
Speaker: Peter Garnovich, University of Notre Dame
Subject: The Spin Cycle: Rapidly Rotating Magnetized White Dwarfs in Close Binaries

The most dynamic types of cataclysmic variable stars are 0nes where the accreting white dwarf is magnetized and its rotation is not locked the binary orbital period. These are often called intermediate polars (IPs) or asynchronous polars (APs) depending on the white dwarfs field strength. I will discuss two of the most exciting and nearby polars and their recent activities. FO Aquarii has been dubbed the "King of the IPs" because of the large amplitude variations produced by the 20 minute spin period of its white dwarf. Recently it has gone into a series of low states that reveal a variety of periodicities. The low states may be related to the long-term evolution of the spin rate of its white dwarf. The second star, AR Scorpii, is a one-of-a-kind white dwarf pulsar. This unique system was identified only four years ago, and the source of its light variations are still in dispute.

Faculty Host: Patrick Kelly
Speaker: Jenna Tonn, History - Boston College
Subject: Being "One of the Boys": Manliness and Experimental Zoology in Boston
Refreshments served at 3:15 p.m.
3:35 pm:
The seminar will be on Tuesday this week. Note change of time and date next week only.
4:40 pm:
Speaker: Paul Crowell, Condensed Matter

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