Physics and Astronomy Colloquium 2017-2018

Thursdays, 4:00-5:00 pm

1-434 Physics and Astronomy (map)

Reception from 3:30-4:00 p.m.
(unless otherwise posted)

For more information, contact Jay Hauser


Fall 2017


Thursday, October 5, 2017

APS Bridge Program: Changing the Face of Physics Graduate Education

Theodore Hodapp

American Physical Society (APS)


In nearly every science, math, and engineering field there is a significant falloff in participation by underrepresented minority (URM) students who fail to make the transition between undergraduate and graduate studies.  The American Physical Society (APS) has realized that a professional society can erase this gap by acting as a national recruiter of URM physics students and connecting these individuals with graduate programs that are eager to a) attract motivated students to their program, b) increase domestic student participation, and c) improve the diversity of their program.  Now in its fifth year the APS has placed enough students into graduate programs nationwide to eliminate this achievement gap.  The program has low costs, is popular among graduate programs, and has inspired other departments to adopt practices that improve graduate admissions and student retention. This presentation will review project activities, present data that demonstrate effectiveness, and discuss future actions.

This material is based upon work supported in part by the National Science Foundation under Grant No. (NSF-1143070).


Thursday, October 12, 2017 - 4:00pm to 5:00pm

Searches for new TeV resonances decaying to electroweak bosons with the CMS detector at the highest LHC energies

Michalis Bachtis

University of California, Los Angeles


After the discovery of the Higgs boson in 2012, the priority of the experiments at CERN’s large hadron collider is to search directly for new physics beyond the Standard Model at the highest energies attainable. The current data-taking at  the LHC is at a center of mass energy of 13 TeV, about 1.6 times higher than in 2012, and has been extremely successful with twice as many proton collisions already recorded. This opens new frontiers in both energy and intensity enabling searches for heavy new particles with masses of several  TeV, more than ten times heavier than the heaviest known elementary particle, the top quark. Meanwhile, precision measurements of Standard Model processes indicate that searching mass scales at least this high is probably required to find new physics. My group’s latest results using the full dataset of the Compact Muon Solenoid experiment will be presented along with an overview of my group’s plans for upgrading the capabilities of the CMS detector that are essential to maintain good quality physics output in even higher beam intensities.


Thursday, October 19, 2017


Thursday, October 26, 2017 - 4:00pm to 5:00pm

Seeking ultra-high energy neutrinos in Antarctica with the radio detection technique

Amy Connolly

The Ohio State University


Ultra-high energy neutrinos ($>10^{18}$~eV) are uniquely capable of probing the most energetic astrophysics sources at cosmic distances, and fundamental physics at center-of-mass energies beyond what is probed by current particle accelerators.  The IceCube Neutrino Observatory at South Pole has announced the first measurements of a neutrino flux of astrophysical origin up to approximately $10^{15}$~eV through an optical signature.  In the last two decades, the radio technique has emerged as the most promising way to detect enough neutrinos in the UHE regime to extract the wealth of information that they carry about astrophysics and particle physics. I will present the latest developments in the field in terms of the experiments, analytical techniques and theoretical groundwork that are bringing us ever closer to the era of UHE neutrino astronomy.  I will also present some first attempts to study the radio sky with our antenna arrays, and I will also introduce some new ideas that our group at OSU is developing to use genetic algorithms in both the design of our projects and in data analysis.  

Thursday, November 2, 2017 - 4:00pm to 5:00pm

Ultrashort meets Ultracold (in the Ultraviolet)

Wesley Campbell

University of California, Los Angeles


By using narrow-band lasers to damp atomic motion, samples of atoms and a few molecules can be produced routinely at sub-millikelvin temperatures. These "ultracold" atoms can be used as quantum sensors, simulators of quantum many-body physics, and precision probes of fundamental physics.  Likewise, "ultrashort" pulse broadband lasers have been employed to study vibrational and electronic motion on extremely short timescales.  The contrast between the spectral widths (or, equivalently, timescales) of these two types of lasers has largely led to the development of separate ultracold and ultrashort communities.  However, progress in merging these two fields has already yielded some unexpected advances, and new work along these lines shows further promise.  Among the surprises, we will discuss the extension of laser-cooling to chemically-prevalent atoms, the non-destructive observation of harmonic electron motion in a single atom, phonon lasing ("phasing?") from trapped ions, and the generation of strong, stimulated optical forces for the deceleration of molecular beams.

Thursday, November 9, 2017 - 4:00pm to 5:00pm

New Windows into the Strong Interaction

Iain Stewart

Massachusetts Institute of Technology


The strong interaction is described by a remarkable theory called Quantum Chromodynamics (QCD), a fully consistent quantum field theory at all distance scales which gives rise to interesting emergent phenomena.  It plays a crucial role in a variety of interesting physical processes, from binding together quarks and gluons in the proton, to the evolution of matter in the early universe, to producing streams of collimated particles called jets in high energy collisions.  Precise control over the strong interaction is necessary for studies of the Higgs boson, as well as for measuring the fundamental parameters of the standard model of particle and nuclear physics.   In this talk I will describe modern developments that enable precision control of the strong interaction in certain situations, as well as a number of important open questions.   Examples will include enhancing our understanding of jet data to dramatically improve the measurement of one of the fundamental parameters of nature, the strong interaction coupling constant, and improving predictions for proton collisions to strengthen our ability to hunt for new particles and forces at very short distances.



Thursday, November 16, 2017 - 4:00pm to 5:00pm

Rewards are worth the Risk: Working in Direct Dark Matter Detection

Kimberly Palladino

University of Wisconsin - Madison


For particle physicists, determining the nature of Dark Matter is one of the greatest open mysteries. An abundance of astrophysical evidence indicates that the matter density of the universe is dominated by a new form of matter, which played a key role in growth of large scale structure. One candidate for Dark Matter is the Weakly Interacting Massive Particle (WIMP). We hope to detect WIMPS by seeing them scattering off of the target materials in our detectors. Liquid xenon has proved itself an excellent target, and LZ is a dual-phase TPC that will begin taking science data in 2020.  Much of the originally proposed parameter space for WIMPS has been excluded over the past few decades, so I will also delve into the sociology of working on direct dark matter searches.


Thursday, November 23, 2017 - Thanksgiving break


Thursday, December 7, 2017 - 4:00-5:00 p.m.




Winter 2018

Thursday, January 18, 2018 - 4:00-5:00 p.m.


What happened 13.8 billion years ago?

Paul Steinhardt

Princeton University)


According to the prevailing view, the universe sprang into existence 13.8 billion years ago in a sudden violent event known as the big bang; and this was soon followed by a brief period of accelerated expansion, known as inflation, which set the large-scale properties of the universe.  In this talk, we will explain the reasons why this idea fails and present a simple alternative – replace the big bang with a bounce and eliminate the need for inflation.   


Thursday, January 25, 2018 - 4:00-5:00 p.m.


Cell mechanical phenotype in cancer: from screening cells to disease biophysics

Amy Rowat

University of California, Los Angeles


Cell mechanical phenotype, or ‘mechanotype’, determines how physical forces are transduced into the cell, and can also signal a transformation in a cell’s physiological state, such as in malignant transformation. If we could obtain higher throughput measurements of cell mechanotype, this would enable a deeper understanding of the molecular origins of cell mechanical properties, as well as screening based on mechanotype. To address these needs, we have used insights from physics to develop a mechanotyping platform that enables us to extract measurements of single cell elastic modulus and fluidity, and to screen cells based on their mechanotype. I will discuss how we are applying our fluidic-based deformability methods to develop a deeper understanding of cell mechanotype in cancer progression. One example application is our discovery that stress hormones, which promote metastasis in mice, also elicit changes in cell mechanical properties: we find that breast cancer cells treated with isoproterenol become stiffer due to actin remodeling, myosin II activity, and increased calcium. Using assays to measure cell invasion through in vitro protein networks, we also discovered that these stiffer isoproterenol-treated breast cancer cells are more invasive. Taken together, our results provide insight into how the mechanical phenotype of cancer cells is associated with their functional behavior.


Thursday, February 1, 2018 - 4:00pm to 5:00pm

Black holes gold rush.

Alexander Kusenko

University of California, Los Angeles


Recent discoveries promise to revolutionize our understanding of black holes, their origin, and their signals.   I will discuss the signals of giant black holes, as well as the possibility that small black holes created in the early universe make up the cosmological dark matter and contribute to synthesis of heavy elements, including gold. 


Thursday, February 8, 2018 - 4:00pm to 5:00pm

Physics of the auditory system

Dolores Bozovic

University of California, Los Angeles

The inner ear constitutes a remarkable biological sensor that exhibits nanometer-scale sensitivity of mechanical detection. The first step in auditory processing is performed by hair cells, which act as transducers that convert minute mechanical vibrations into electrical signals that can be sent to the brain. This conversion involves the opening of ion channels, which are mechanically gated. The hair cells operate in a viscous environment, but can nevertheless sustain oscillations, amplify incoming signals, and even exhibit spontaneous motility. The thermodynamic requirements of this indicate the presence of an underlying active process that pumps energy into the system. Theoretical models have proposed that a hair cell constitutes a nonlinear system, and allow us to describe and predict how they respond to incoming sound.

Our experiments explore the physical mechanisms behind the detection of very weak signals, and describe them using models based on dynamical systems theory. We explore the different bifurcations that characterize hair bundle activity, and study how they affect phase-locking to incoming signals. We demonstrate experimentally that bundles can phase-lock to a broad range of frequencies, in various mode-locking ratios. Further, we demonstrate the presence of chaos in the underlying dynamics of active bundles, and explore its impact on the sensitivity of detection. Secondly, we explore the interaction between active bundle mechanics and the electrical circuit comprised of somatic ion channels. Finally, we study the fluctuation dynamics of actively oscillating hair bundles.

Thursday, February 15, 2018 - 4:00-5:00 p.m.

CANCELLED - There is no colloquium scheduled for this week.

Thursday, March 1, 2018 - 4:00-5:00 p.m.

Statistical Mechanics, Localization and Periodically Driven Quantum Systems
Shivaji Sondhi

Princeton University

The statistical mechanics of equilibrium systems is characterized by two fundamental ideas: that closed systems approach a late time thermal state and that of phase structure wherein such late time states exhibit singular changes as various parameters characterizing the system are changed. Recent progress has established generalizations of these ideas which apply to periodically driven, or Floquet, closed quantum systems. I will describe this progress, which centrally uses other recent advances in our understanding of many body localization. I will describe how it has resulted in the discovery of entirely new phases such as the Pi-spin glass/Floquet time crystal which exist only in driven quantum system.


Thursday, March 8, 2018 - 4:00-5:00 p.m.

Atomic Resolution Analysis of Single Atoms in 2D Materials using Transmission Electron Microsco

Jamie Wagner

Oxford University


Measuring a material atom-by-atom provides unrivalled insights into its structure and how this impacts its properties. Transmission electron microscopy is one of the leading approaches to probe individual atoms in solids to measure their position, elemental type, bond length, charge state, and local electric field. I will discuss our recent advances in sub-Angstrom resolution measurements of nanomaterials using aberration corrected transmission electron microscopy (TEM). I will show how state-of-the-art electron-optics provide electron probes that can interact with single atoms, using a combination of annular dark field scanning TEM with electron energy loss spectroscopy (EELS). The main materials of focus are 2D systems, such as graphene, MoS and WS2. I will show how we can measure the local electric field around single atoms in MoS2 using direct electron detectors to capture 4D data sets that are rich with information. Analysis around defects and dopants in 2D materials will be presented, with atom-by-atom EELS mapping and measurements of local perturbations to electric fields. In-situ TEM is also shown for nanoelectronic devices to understand the mechanisms of electrical breakdown in monolayer MoS2, and how high temperature transformations occur in 2D materials in real time. I will discuss grain boundaries, single atom dopants, vacancy defects, dislocations, buckling, strain maps, interlayer stacking structures, atomically sharp cracks, inversion domains, 1D nanowires, and nanopores in 2D materials at the atomic level. 

Thursday, March 15, 2018 - 4:00-5:00 p.m.

Quantum Magnetism from the Iron Age to Today

Daniel Arovas

University of California, San Diego


The quantum theory of magnetism has provided many durable paradigms for quantum phases of matter, including intrinsically quantum disordered states, symmetry-protected topological phases, and quantum spin liquids.  In this lecture, I will review some of the history and highlights of this very rich field.





Spring 2018

 Thursday, April 5, 2018 - 4:00pm to 5:00pm

Old Galaxies, New Surprises

Alexie Leauthaud

University of California, Santa Cruz


I will present new results from the ongoing Hyper Suprime Cam survey currently being carried out by Subaru. The HSC survey is an unprecedented effort to map 1400 deg^2 in 5 bands to i~26. This unique combination of depth and area enables us to study the individual light profiles of several thousand super massive galaxies (M*>11.6 Msun) to 100 kpc and beyond. We show that massive galaxies are not self similar and that instead their light profiles are diverse. This diversity is not random: using weak gravitational lensing we make a remarkable discovery. There is a tight correlation between the shapes of galaxy light profiles and their host dark matter halo mass. Deep imaging is critical for measuring the total light from these galaxies. With better luminosity measurements in hand, I will show that there is a much tighter relation between the luminosities of super massive galaxies and dark matter halo mass that previously recognized.  Finally, I will discuss how our results have the potential to transform optical galaxy cluster detection and the way we use cluster surveys to constrain dark energy.



Thursday, April 19, 2018 - 4:00pm to 5:00pm

Is Basketball Scoring Just a Random Walk?

Sid Redner

Boston University and Santa Fe Institute


Watching basketball is nearly the same as watching repeating coin tossings!  By analyzing recently available data from recent NBA basketball seasons, basketball scoring during a game is well described by a continuous-time anti-persistent random walk, with essentially no temporal correlations between successive scoring events.  We show how to calibrate this model to account for many statistical season-long metrics of NBA basketball.  As further fillustrations of this random-walk picture, we show that the distribution of times when the last lead change occurs and the distribution of times when the score difference is maximal are both given by the celebrated arcsine law -- a beautiful and surprising property of random walks.  We also use the random-walk picture to construct the criterion for when a lead of a specified size is "safe" as a function of the time remaining in the game.  The obvious application to game-time betting is left as an exercise for the interested.