Physics and Astronomy Calendar

Week of Monday, February 19th 2018


Monday, February 26th 2018
12:15 pm:
There will be no seminar this week.

Tuesday, February 27th 2018
12:20 pm:
Space Physics Seminar in Tate 301-20
Practice Talks for the upcoming Chapman Conference on Particle Dynamics in the Earth's Radiation Belts.
3:30 pm:
Speaker: Samuel Lederer, MIT
Subject: High temperature superconductivity and strange metal behavior near a metallic quantum critical point

t has long been conjectured that quantum critical points (QCPs) are at the root of some of the most fascinating phenomena in the solid state, including the high temperature superconductivity and “strange metal” behavior of cuprate superconductors. Though much progress has been made in the theory of QCPs, those which occur in metals (and are likely relevant to the high temperature superconductors) are still poorly understood despite more than four decades of effort. Using Quantum Monte Carlo techniques, my collaborators and I have performed the first numerically exact simulations of a model which realizes a metallic QCP towards an Ising nematic ordered phase. I will discuss our results, which include numerous phenomena already observed in experiment, and comment on future avenues towards a solution of this difficult and rich problem in quantum statistical mechanics.

Faculty Host: Rafael Fernandes

Wednesday, February 28th 2018
1:25 pm:
Speaker: Various speakers
Subject: APS March Meeting Practice Talks
To be announced.

Thursday, March 1st 2018
10:10 am:
Biophysics Seminar in 120 PAN
Speaker: Tanner Akkin, Associate Professor of Biomedical Engineering, University of Minnesota
Subject: Development of a Serial Optical Coherence Scanner for Visualizing and Mapping the Brain with Microscopic Resolution

The feasibility of mapping and imaging the brain with microscopic resolution is presented. A serial optical coherence scanner, which combines a polarization-sensitive optical coherence tomography and a tissue slicer, distinguishes white matter and gray matter and visualizes nerve fiber tracts that are as small as a few tens of micrometers. The technique utilizes the retardance contrast that arise due to the myelination of nerve fibers and the axis orientation contrast that determine the 2D orientation of the nerve fibers, and the technique can be adapted to measure the inclination angle of the fiber, completing the 3D orientation. This scanner could reveal biomarkers for disease onset and progression, and support development of therapeutics.

Speaker: Evan Tyler
4:00 pm:
Speaker: Sara Seager, MIT
Subject: Mapping the Nearest Stars for Habitable Worlds
Joint Colloquium with Earth Sciences (Nier Lecture). Note later start time.

Bio:

"Sara Seager is a planetary scientist and astrophysicist at the Massachusetts Institute of Technology where she is a Professor of Planetary Science, Professor of Physics, Professor of Aerospace Engineering, and holds the Class of 1941 Professor Chair. She has pioneered many research areas of characterizing exoplanets with concepts and methods that now form the foundation of the field of exoplanet atmospheres. Her present research focus is on the search for life by way of exoplanet atmospheric “biosignature” gases. Professor Seager works on space missions for exoplanets including as: the PI of the CubeSat ASTERIA; the Deputy Science Director of the MIT-led NASA Explorer-class mission TESS; and as a lead of the Starshade Rendezvous Mission (a space-based direct imaging exoplanet discovery concept under technology development) to find a true Earth analog orbiting a Sun-like star. Among other accolades, Professor Seager was elected to the US National Academy of Sciences in 2015, is a 2013 MacArthur Fellow, is a recipient of the 2012 Sackler Prize in the Physical Sciences, and has Asteroid 9729 named in her honor."

Abstract:

Thousands of exoplanets are known to orbit nearby stars and small rocky planets are established to be common. The ambitious goal of identifying a habitable or inhabited world is within reach. But how likely are we to succeed? We need to first discover a pool of planets in their host star’s “extended” habitable zone and second observe their atmospheres in detail to identify the presence of water vapor, a requirement for all life as we know it. Life must not only exist on one of those planets, but the life must produce “biosignature gases” that are spectroscopically active, and we need to be able to sort through a growing list of false-positive scenarios with what is likely to be limited data. The race to find habitable exoplanets has accelerated with the realization that “big Earths” transiting small stars can be both discovered and characterized with current technology, such that the James Webb Space Telescope has a chance to be the first to provide evidence of biosignature gases. Transiting exoplanets require a fortuitous alignment and the fast-track approach is therefore only the first step in a long journey. The next step is sophisticated starlight suppression techniques for large ground-and space-based based telescopes to observe small exoplanets directly. These ideas will lead us down a path to where future generations will implement very large space-based telescopes to search thousands of all types of stars for hundreds of Earths to find signs of life amidst a yet unknown range of planetary environments. What will it take to identify such habitable worlds with the observations and theoretical tools available to us?

Nier Info:

Professor A.O. Nier

A.O. Nier served as a highly distinguished faculty member of the Physics Department for 42 years starting in 1938. He was actively involved in research up to the time of his death in 1994. A firm believer in “pursuits of knowledge - in areas which cross traditional lines” he had an enormous impact on the geological sciences by his pioneering work on isotope abundances and measurements of many elements which are used in radiometric age determinations of geologic materials. He received many national and international awards in recognition of his discoveries and contributions to Physics, Geological Sciences and many other fields.


Friday, March 2nd 2018
10:10 am:
Nuclear Physics Seminar in Tate 201-20
To be announced.
12:20 pm:
Speaker: Various speakers
Subject: APS March Meeting Practice Talks
Speaker: Andrew Spray, (IBS, Daejon, Korea)
Subject: Constraints and Phenomenology of Semi-Annihilating Dark Matter

Semi-annihilation describes processes with an initial state of two dark matter particles, and a final state of one plus standard model states. It is a generic feature of dark matter whenever the symmetry group enforcing stability is not a discrete Z2. Semi-annihilation changes the expected signals in current dark matter searches. With the bounds on standard thermal dark matter becoming very strong, now is the ideal time to ask to what extent those bounds apply to semi-annihilation, and what interesting parameter space remains. In this talk, explore the parameter space in a generic, bottom-up approach. We discuss the subtleties involved with semi-annihilation of fermionic dark matter, the role of additional unstable dark sector particles, and the interplay of semi-annihilation and the non-perturbative Sommerfeld effect. We discuss how semi-annihilation may relate to various anomalies seen in cosmic ray searches. Finally, we use an effective field theory approach to place limits in as model-independent a fashion as possible. We find that current searches are effective for processes with coloured final states, but significant model space for semi-annihilation still remains.

Speaker: Dr. Mateusz Ruszkowski, U. Michigan
Faculty Host: Thomas W. Jones
Speaker: Alisa Bokulich, Department of Philosophy, Boston University
Subject: "Using Models to Correct Data: Paleodiversity and the Fossil Record"
Refreshments served at 3:15 p.m.

It has long been recognized that models play a crucial role in science, and in data more specifically. However, as our philosophical understanding of theoretical models has grown, our view of data models has arguably languished. In this talk I use the case of how paleontologists are constructing data-model representations of the history of paleodiversity from the fossil record to show how our views about data models should be updated. In studying the history and evolution of life, the fossil record is a vital source of data. However, as both Lyell and Darwin recognized early on, it is a highly incomplete and biased representation. A central research program to emerge in paleontology is what D. Sepkoski has called the “generalized” (or what I prefer to call “corrected”) reading of the fossil record. Building on this historical work, I examine in detail the ways in which various models and computer simulations are being used to correct the data in paleontology today. On the basis of this research I argue for the following: First, the notion of a data model should be disentangled from the set-theoretic, ‘instantial’ view of models. Data models, like other models in science, should be understood as representations. Second, representation does not mean perfectly accurate depiction. Data models should instead be assessed as adequate-for-a-purpose. Third, the ‘purity’ of a data model is not a measure of its epistemic reliability. I conclude by drawing some parallels between data models in paleontology and data models in climate science.

3:35 pm:
To be announced.
4:40 pm:
There will be no seminar this week.

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