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: Marianna Safronova, University of Delaware
Hosts: S. Aubin
November 3, 2023 (Friday) 4:00-5:00p.m.
Speaker: Bryan Ramson, Fermilab
Hosts: P. Vahle
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
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
Hosts: C. Monahan
December 8, 2023 (Friday) 4:00-5:00p.m.
Speaker: Josh Ruderman, NYU
Hosts: M. Sher