Physics & Astronomy Colloquium

Thursdays, 4:00-5:00 pm

Virtual Colloquium Meetings are held via Zoom. Meeting information will be sent in email. You may watch past presentations by clicking the title link when available.

For more information, contact Robijn Bruinsma.

Click here for the 2019-2020 archived Physics & Astronomy Colloquium.

Fall 2020
Thursday, October 8, 2020

Nuclear Femtography - A new frontier of science and technology
Jianwei Qiu
Jefferson Lab

The proton and neutron, known as nucleons, are the fundamental building blocks of all atomic nuclei that make up essentially all the visible matter in the universe, including the stars, the planets, and us. Nucleons have a complex internal structure. Within Quantum Chromodynamics, nucleons emerge as strongly interacting and relativistic bound states of quarks and gluons. Both theory and experimental technology have now reached a point where we are capable of exploring the inner structure of nucleons and nuclei at sub-femtometer distance, leading to the newly emerging science of nuclear femtography. In this talk, I will demonstrate that the newly upgraded CEBAF facility at Jefferson Lab and the Electron-Ion Collider, which the US Department of Energy recently approved for construction at Brookhaven National Lab, will be two complementary and necessary facilities for exploring the science of nuclear femtography. They are powerful tomographic scanners and/or microscopes able to precisely image the inner structure of nucleon and nuclei with a sub-femtometer resolution. They will help us address the most compelling unanswered questions about the elementary building blocks of our visible world, and are capable of taking us to the frontier of the Standard Model.

Thursday, October 15, 2020

Controlling the quantum states of atoms to probe fundamental physics
Paul Hamilton
University of California, Los Angeles

Modern techniques to control the quantum states of atoms have enabled measurements with an unprecedented precision and accuracy. This ability makes atomic systems attractive for a range of applications including quantum sensing, quantum computation, and quantum simulation. I will discuss ongoing experiments at UCLA harnessing this control of atoms to make novel gravitational, rotational, and magnetic sensors, and their application to searches for particles and fields beyond the Standard Model including sterile neutrinos, dark matter, and dark energy.

Thursday, October 22, 2020

The renaissance of jet physics
Zhongbo Kang
University of California, Los Angeles

The particle collisions observed in high energy colliders are dominated by the phenomenon of jets. These are collimated sprays of particles that result directly from quantum chromodynamics (QCD). Following advances in both experimental techniques and theory, the study of jets has become a powerful tool for the exploration of fundamental properties of QCD under different conditions, and for the search for new phenomena in high-energy collisions. Jets can now be characterized not just by their overall direction and energy but also by their internal substructure. Jet physics is at the forefront of phenomenology studies at the Large Hadron Collider (LHC) and at the future Electron Ion Collider (EIC). In this talk, I will highlight novel experimental opportunities and new theoretical studies of the physics of jets, how they affect probes of QCD at the LHC and studies of the quantum imaging of protons at the EIC.

Thursday, October 29, 2020

Investigating the energy frontier of Particle Physics while analyzing 40 million proton collisions per second in real time
Michalis Bachtis
University of California, Los Angeles

The Large Hadron Collider has recently completed its second run collecting an enormous dataset of proton collisions at the center of mass energy of 13 TeV. The new dataset provides a unique opportunity to search for heavy new particles that are predicted by several theoretical models and could not be produced in the energies achieved before. Recent results on those searches performed by the UCLA group will be presented. In parallel with data analysis, an established new instrumentation effort towards the upgrade of the CMS experiment will be presented, featuring high throughput processors built at UCLA that can analyze more than 3 Tb/s of data in real-time. Finally an extension of this instrumentation program will be presented, where similar technology targeting 5G wireless is used to perform real-time RF signal processing with applications in particle accelerators and other areas of experimental physics.

Thursday, November 5, 2020

Quantum control of spins in silicon
Mark Eriksson
Wisconsin Quantum Institute and University of Wisconsin-Madison

Quantum computing is based on the manipulation of two-level quantum systems, or qubits. In most approaches to quantum computing, qubits are as much as possible isolated from their environment in order to minimize the loss of qubit phase coherence. The use of nuclear spins as qubits is a well-known realization of this approach. In a radically different approach, quantum computing is also possible for strongly coupled multi-electron spin 1/2 systems, as realized in silicon-based devices. In this talk I will present both a historical overview of how quantum manipulation in silicon has developed, as well as the latest results from both our group at Wisconsin and from around the world. I will also discuss an interesting scientific case study, comparing some limiting cases: qubits composed of single-spins, be they electron or nuclear, where magnetically-driven manipulation (possibly effective rather than direct) is required, and qubits composed of multiple electrons, for which case direct electric-field manipulation is possible. I will end with a brief discussion of how silicon fits into the broad quantum science and technology ecosystem, which is growing at an astounding rate.

This article in Physics Today discusses closely related material.

Thursday, November 12, 2020

Results from LIGO-Virgo’s third observing run
Jess McIver
University of British Columbia

In less than five years, the field of gravitational wave astronomy has grown from a groundbreaking first discovery to revealing new populations of stellar remnants through distant cosmic collisions. Advanced LIGO and Advanced Virgo’s third observing run, from April 2019 to March 2020, potentially added dozens more known compact object mergers to the eleven confident detections from the first two Advanced-era observing runs. I'll summarize recent results from LIGO-Virgo and their implications, including the recently announced discovery of a 142 solar mass black hole, and discuss challenges for LIGO, Virgo, and KAGRA in this new era of multi-messenger astronomy with gravitational waves.

Thursday, November 19, 2020

Power and Privilege
Sherard Robbins
Visceral Change, LLC

This one-hour presentation has been designed to offer an in depth dialogue around the systems of power and privilege and how they impact our everyday lives, personally, professionally, and academically. This session offers discussion time to define privilege and how those systems serve as predicates for how we interpret normalcy and establish a standard of justification. Through the exploration of power and privilege, participants will gain a better understanding of how to promote inclusivity and social justice among people of all identities.

Thursday, November 26, 2020

Thanksgiving holiday, no colloquium

Thursday, December 3, 2020

"TBA" by Vincenzo Vitelli (University of Chicago)

Thursday, December 10, 2020

"TBA" by Clifford Cheung (Caltech)

Winter 2021
Thursday, January 14, 2021

Affinity maturation of antibodies and the puzzle of HIV spikes
Mehran Kardar
Massachusetts Institute of Technology

Affinity maturation (AM) is the process through which the immune system evolves antibodies (Abs) which efficiently bind to antigens (Ags), e.g. to spikes on the surface of a virus. This process involves competition between B-cells: those that ingest more Ags receive signals (from T helper cells) to replicate and mutate for another round of competition. Modeling this process, we find that the affinity of the resulting Abs is a non-monotonic function of the target (e.g. viral spike) density, with the strongest binding at an intermediate density (set by the two-arm structure of the antibody). We argue that, to evade the immune system, most viruses evolve high spike densities (SDs). This is indeed the case, except for HIV whose SD is two orders of magnitude lower than other viruses. However, HIV also interferes with AM by depleting T helper cells, a key component of Ab evolution. We find that T helper cell depletion results in high affinity antibodies when SD is high, but not if SD is low. This special feature of HIV infection may have led to the evolution of a low SD to avoid potent immune responses early on in infection. Our modeling also provides guides for design of vaccination strategies against rapidly mutating viruses.

Thursday, January 28, 2021

Pushing the limits of hydrodynamics
Pavel Kovtun
University of Victoria

Hydrodynamics is a well-established field with a venerable history. In this talk, I will focus on foundational aspects of hydrodynamics which came to light in recent years. Do the equations of hydrodynamics even make sense? To what degree can the crudeness of hydrodynamics be improved? What about the phenomena that hydrodynamics should describe but fails to? And what about the phenomena that hydrodynamics shouldn't describe, but does?