Fall 2023
September 8, 2023 (Friday) 4:00-5:00p.m.
Speaker: Ibrahima Bah, Johns Hopkins
Hosts: M. Sher
Title: Topological Stars and Gravity
Abstract: In this colloquium I will discuss aspects of microscopic degrees of freedom of gravity and the physical motivation of quantum gravity. While the generic states are quantum mechanical, our goal will be to understand a class of them that are coherent enough to admit classical descriptions in Einstein gravity. The existence of these state require topological structures in spacetime that follow from the dynamics of compact extra dimensions. They behave as ultra-compact objects, dubbed topological stars, which can also model microscopic degrees of freedom of black holes. I will discuss why it is interesting to understand such objects in a new age of black hole astrophysics, and various aspects of their observational properties.
September 22, 2023 (Friday) 4:00-5:00p.m.
Speaker: Steven Cowley, Director of PPPL
Hosts: S. Mordijck
Title: Stability and Meta-stability: a challenge for fusion
Abstract: Instability limits the pressure and the current in fusion plasmas. These limits can be
soft, where the instability effectively prevents the plasma exceeding the limit but does notdisrupt explosively. More problematically, limits can be hard, where the plasma releases considerable amounts of energy explosively to bring it well below the stability limit. I will demonstrate that pressure driven modes can and do exhibit both kinds of behavior. The consequences for fusion will be discussed. Steven Cowley, a theoretical physicist with a focus on fusion energy, became the seventh Director of the Princeton Plasma Physics Laboratory in 2018, and a Princeton professor of astrophysical sciences. He has held positions on both sides of the Atlantic including: President of Corpus Christi College and professor of physics at the University of Oxford and, chief executive officer of the United Kingdom Atomic Energy Authority (UKAEA).
September 29, 2023 (Friday) 4:00-5:00p.m.
Speaker: Yue (Joyce) Jiang, JILA University of Colorado Boulder
Hosts: I. Novikova
Title: Quantum-enhanced sensing for axion dark matter
Abstract: Quantum-enhanced sensors hold promise for accelerating the search for weak signals arising from fundamental physics beyond the Standard Model. For example, a recent experiment used squeezed vacuum noise to double the quantum-limited search rate for the axion, a hypothetical dark matter particle. However, further enhancement of the search rate is inhibited by the fragility of the squeezed state, which is susceptible to losses. In this presentation, I will discuss a more robust quantum-enhanced sensing technique using simultaneous state-swapping and two-mode squeezing interactions, enabling backaction-evading measurement. Our experiment demonstrated an 8-fold speedup for searching a synthetic axion signal compared to the detector operating at the quantum limit. Implementing this enhanced sensing technique in an axion search would enable a much faster sweep through the vast axion parameter space, circumventing quantum noise limit.
October 27, 2023 (Friday) 4:00-5:00p.m.
Speaker: Matt Grau, Old Dominion University
Hosts: S. Aubin
Title: Searching for Symmetry Violation with Molecular Ions
Abstract: Molecules have emerged as powerful instruments for conducting precise tests of fundamental symmetries, such as the search for the electron electric dipole moment (eEDM). However, molecules are generally difficult to trap and cool, making it challenging to perform narrow linewidth measurements with long interrogation times without a complicated laser-cooling setup capable of repumping multiple rovibrational levels. Our approach harnesses molecular ions, which offer distinct advantages. They can be readily stored in ion traps for prolonged durations and sympathetically cooled by laser-cooled atomic ions. Notably, atomic lutetium ions are amenable to direct laser cooling, making them ideal candidates to serve as sympathetic coolants and to form pre-cooled molecular ions. Furthermore, Lu-176 boasts one of the largest nuclear electric quadrupole moments of any long-lived isotope, rendering it exceptionally sensitive to the CP-violating nuclear magnetic quadrupole moment (nMQM). I will describe how we can harness these properties in molecular ions containing lutetium, such as LuOH⁺, to probe new physics through the simultaneous investigation of nMQM and eEDM.
November 3, 2023 (Friday) 4:00-5:00p.m.
Speaker: Bryan Ramson, Fermilab
Hosts: P. Vahle
Title: Reviewing the Physics Program of the Fermilab Modern Modular Bubble Chamber
Abstract: Long-baseline neutrino oscillation experiments present some of the most compelling paths towards beyond-the-standard-model physics through measurement of PMNS matrix elements and observation of the degree of leptonic CP violation. State-of-the-art long-baseline oscillation experiments, like NOvA and T2K, are currently statistically limited, however uncertainty in neutrino-nucleus scattering represents an important source of systematic uncertainty in future experiments like DUNE and Hyper-Kamiokande. Neutrino cross-section uncertainties can be reduced through high-statistics measurement of neutrino interactions on light nuclei, but creating a detector with an appropriate light target has proved elusive since the hydrogen bubble chambers designed in the 70’s. Modern bubble chamber-based dark matter detectors like PICO and the Scintillating Bubble Chamber have demonstrated that advances in sensor technology, computing, and automation would allow a modern bubble chamber to fully utilize the megawatt scale intensity LBNF beam. This talk will review the broad physics program and the construction of a hydrogen bubble chamber for use with neutrinos at Fermilab.
Bio: Bryan Ramson is a neutrino physicist working on the intensity frontier of high-energy particle physics. He works as an associate scientist at Fermilab, where he uses his expertise in medium and high-energy nuclear physics to improve measurements of neutrino oscillations and refine our understanding of neutrino-nucleus interactions. He is a member of two large experimental collaborations: the Fermilab NuMI Off-axis νe Appearance (NOvA) Experiment and the upcoming Deep Underground Neutrino Experiment (DUNE), a future Fermilab experiment. When not directly supporting the measurement of neutrino oscillations, he studies neutrino-nucleus interactions in the NOvA Near Detector and leads an independent R&D project to develop a new generation of hydrogen bubble chambers. Bryan earned dual B.S.’s in Physics and Mathematics, and an M.S. in Atmospheric Sciences from Howard University in Washington, DC. He earned another M.S. and Ph.D. in Applied Physics from the University of Michigan, Ann Arbor. His doctoral work concerned the study of nuclear anti-matter and occurred as a visiting scholar on the Argonne/Fermilab particle physics experiment, E906/SeaQuest. Bryan has a strong commitment to serving society scientifically, as well as socially. Before matriculating at Michigan he was a visiting scholar at Earth Sciences Division of NASA Goddard from Howard University, working primarily on the measurement of cloud properties in the Baltimore-Washington corridor and the US Southern Great Plains region. He currently serves as the co-Chair of the Fermilab Saturday Morning Physics program and has engaged in various forms of community engagement around the Chicagoland area especially as it concerns science outreach and local community organizing. Bryan is a native of New Orleans, LA, coming of age in the Seventh and Ninth Wards of the city. He currently resides in the West Garfield Park neighborhood on the West Side of Chicago, Illinois. When he is not thinking about quarks and leptons or actively working for a better future, he enjoys popular television and movies, speculative fiction, exercise, performance driving, and video games.
November 10, 2023 (Friday) 4:00-5:00p.m.
Speaker: Raghav Kunnawalkam-Elayavalli, Vanderbilt University
Hosts: C. Monahan
Title: Back to fundamental QCD - how do quarks and gluons evolve in space and time?
Abstract: Collider experiments have proven themselves immensely useful in studying the behavior of fundamental particles such as quarks and gluons. The last few years in particular have seen a push towards an exploration of QCD, that has hitherto been inaccessible, via innovative experimental techniques to access the multi-scale parton evolution and eventually even shed light on hadronization mechanisms. In this talk, I start with a pedagogical overview of jets and their structure and highlight recent measurements from experiments at both RHIC and LHC. In the context of heavy ion collisions, jets have been advertised for the past two decades as a useful tool for quark-gluon plasma (QGP) tomography. This quest has had its fair share of roadblocks but I share the community's roadmap to the next-generation of measurements with the sPHENIX detector at RHIC, that have untapped potential to extract of the QGP's microscopic transport properties and in mapping its space-time evolution. Finally, I cover the impact of the upcoming Electron Ion Collider where these novel techniques and experimental precision lead to imaging both the perturbative and non-perturbative QCD regimes, allowing us unprecedented access into color confinement and hadronization.
Bio - Dr. Raghav Kunnawalkam Elayavalli is an assistant Professor of Physics in the department of Physics and Astronomy at Vanderbilt University since fall of 2022. They work primarily in the field of high energy nuclear physics since their masters at Stony Brook University back in 2011. Their masters thesis was in the setup of a simulation package for the future Electron Ion Collider called EICROOT where they studied the interaction of lepton-flavor violating processes. After doing their PhD work at Rutgers University (2013-2017) with the CMS experiment at CERN, they moved their research back to RHIC science during postdoc positions at Wayne State University (2017-2022) and Yale/BNL (2020-2022) with the STAR collaboration. At Vanderbilt University, their main focus is on the new sPHENIX experiment at RHIC and the CMS experiment at LHC along with EIC physics heading into the future. They were recently awarded the DOE Early Career award for 2023 focused on measurements of the space-time evolution of quarks and gluons at RHIC. They are also members of the JETSCAPE collaboration which includes both theorists and experimentalists focused on creating advanced analysis and statistical toolkits to extract fundamental properties of the QGP.
November 17, 2023 (Friday) 4:00-5:00p.m.
Speaker: John V. Shebalin, Affiliate Research Professor, George Mason University
Hosts: S. Mordijck
Title: Statistical Solution of the Dynamo Problem
Abstract:
The ‘dynamo problem’ asks the question: How do planets and stars produce a quasi-stationary, energetic dipole magnetic field? We will show that this problem is solved by applying statistical mechanics to magnetohydrodynamic (MHD) turbulence. Joseph Larmor hypothesized in 1919 that the solution lay in a ‘self-excited dynamo’ within the Earth or the Sun. He conjectured that the dynamo was not mechanical, like Faraday's dynamo, but was thought to arise from ‘convective circulation’ and ‘electric currents.’ In 1956, William Elsässer saw that for ‘the dynamo problem, that is ... the problem of generating and maintaining magnetic fields which draw their energy from the mechanical energy of the fluid, the nonlinear character of the equations is altogether essential’, as it produces ‘turbulence, the most conspicuous of the nonlinear phenomena of fluid dynamics.’ Elsässer realized that statistically stationary MHD turbulence was fundamental to the solution of the dynamo problem, rather than ‘rigorously stationary flow’ (i.e., a kinematic dynamo). He added that there were ‘qualitative conditions, three in number, requisite for the operation of ... dynamo models’; these conditions were (1) large linear dimensions, (2) rotation and (3) convection. The first condition implies that Reynolds numbers are sufficiently large; the second that rotation axis and magnetic dipole vector appear on average to be aligned in planets and stars; and the third, that convection is the dynamo’s source of energy. MHD turbulence, due to conditions (1) and (3) is expected to occur in planetary liquid cores and stellar interiors when global magnetism is observed, and must be an integral part of any dynamo model. Although condition (2), rotation, is prevalent in planets and stars and a close alignment often occurs between the dipole moment vector and the rotation axis, rotation is not essential for dynamo action. What is critical is magnetic helicity, which is found to be directly proportional to dipole energy. Thus, MHD turbulence, per se, is the dynamo. Here, we will review the mathematical model, as well as the theoretical and computational results that lead to this conclusion.
Bio: John V. Shebalin received his Ph.D. in Physics from W&M in 1982. Part of his dissertation entitled, “Anisotropy in MHD Turbulence Due to a Mean Magnetic Field,” appeared in a Journal of Plasma Physics (JPP) article of the same title in 1983; this appears to be the most citied paper ever published by JPP. He held positions in industry, academe and government, retiring from NASA as an Astrophysicist in 2017 after 30 years of service. He is currently an Affiliate Research Professor at the Space Weather Lab, Dept. of Physics & Astronomy, George Mason University.
December 1, 2023 (Friday) 4:00-5:00p.m.
Speaker: Julia Phillips,Vice President and Chief Technology Officer, Sandia Nat'l Laboratories (retired)
Hosts: C. Monahan
Title: Lessons from a Life in Science & Engineering outside of Academia
Abstract: I have been most fortunate to have had, and to continue to have, a fascinating, rewarding, and varied career and life. While my career has always centered on science, it has not taken many of the paths that students probably first consider as they plot their own careers. I will give a very brief overview of my career, factors affecting the choices I made, and circumstances that made certain opportunities open to me. This will lead me to pose questions that every individual has to answer for themselves about their personal priorities that may guide them in their career decisions. I will then discuss general advice about things that make a student or postdoc a desirable candidate (especially in a non-academic position) and that continue to open doors for them throughout their career. I will illustrate some of these thoughts with examples from my career or from the development of young scientists and engineers I have mentored.
December 8, 2023 (Friday) 4:00-5:00p.m.
Speaker: Josh Ruderman, NYU
Hosts: M. Sher
Title: Phases of Particle Dark Matter
Abstract: Dark matter is believed to make up most of the matter in our Universe, but its particle origin remains a mystery. A favorite candidate is the so-called Weakly Interacting Massive Particle (WIMP), but a diverse set of experiments are rapidly closing the available parameter space for WIMPs. I will show that small changes to the assumptions about how dark matter was produced in the early Universe lead to very different dark matter masses and interaction strengths. I will chart ``phase diagrams” for the production of dark matter with a thermal or non-thermal origin. I will explain how different phases of dark matter production map onto different experimental prospects.
