Events at Physics |
Events During the Week of October 8th through October 15th, 2023
Monday, October 9th, 2023
- Plasma Physics (Physics/ECE/NE 922) Seminar
- “Some Recent Developments of Compressible MHD Turbulence with Applications to Space and Astrophysical Plasmas”
- Time: 12:00 pm - 1:15 pm
- Place: 1610 Engineering Hall
- Speaker: Hui Li, Los Alamos National Laboratory
- Abstract:
in collaboration with K. Yuen, S. Du (LANL); Z. Gan, X. Fu (NMC), H. Yan (DESY)
Recent Parker Solar Probe (PSP) measurements of the near-Sun solar wind have provided in-situ measurements of compressible magnetized turbulence. Understanding their properties has led us to examine several physical processes including the temporal properties of compressible MHD turbulence, scalings of density fluctuations and the magnetic energy dissipation via compressible effects in reconnecting regions. Specifically, through 4D FFT analysis (temporal plus 3D spatial) of compressible MHD turbulence, most fluctuations are found to have very low frequencies with finite wavenumbers and they do not follow the dispersion surfaces of linearized MHD waves. We propose a broadened Lorentzian model in frequency dependence and find quite good agreement between the theory and simulations (Yuen et al. 2023). One implication of this understanding is the re-examination of the mechanisms responsible for density fluctuations in compressible turbulence, along with the properties observed by PSP (Fu et al. 2023). In addition, we present simulations of 3D reconnection to demonstrate that the compressible processes give rise to an additional phase that produces even more overall magnetic energy conversion than that by the initial relaxation of magnetic curvature (Du et al. 2022). These processes could play a role in the continued heating of the background plasma such as solar wind and magnetized outflows. - Host: Prof. Steffi Diem
Tuesday, October 10th, 2023
- Council Meeting
- Physics Council Meeting
- Time: 3:00 pm - 4:00 pm
- Place: 2314 Chamberlin Hall
- Speaker: Mark Eriksson, UW - Madison
- Host: Mark Eriksson
Wednesday, October 11th, 2023
- Department Meeting
- Time: 12:15 pm - 1:00 pm
- Place: B343 Sterling Hall
- Speaker: Mark Eriksson, UW-Madison
- agenda to come a day or so before the meeting.
- Host: Mark Eriksson
- Wisconsin Quantum Institute Seminar
- Macroscopic Objects in a Quantum Regime
- Time: 3:30 pm - 5:00 pm
- Place: Discovery Building, DeLuca Forum
- Speaker: Eugene Simon Polzik, Niels Bohr Institute – University of Copenhagen
- Abstract:
Studies of extreme cases within quantum mechanics have always been particularly attractive. How macroscopic can objects be and still demonstrate unique quantum features, such as entanglement? What are the real limits of measurement precision in quantum mechanics? I will review our experiments where macroscopic objects are driven deep into the quantum regime. Observation of a quantum trajectory of motion in a quantum reference frame with, in principle, unlimited accuracy will be presented. A concept of a reference frame with an effective negative mass required for such observation will be introduced. Generation of an entangled Einstein-Podolsky-Rosen state between distant mechanical and atomic oscillators and progress towards application of those ideas to gravitational wave detection will be reported. Another challenge within quantum physics of macroscopic objects is generation of Fock states corresponding to single quantum excitations of an oscillator. Progress along those lines with states of motion and of a macroscopic spin will be presented.
This event starts at 3:30pm with refreshments, followed at 3:45pm by a short presentation by Akbar Safari (postdoc Saffman group) titled "Remote atom-atom entanglement and quantum networking". The invited presentation starts at 4pm.
- Host: Mark Saffman
Thursday, October 12th, 2023
- Astronomy Colloquium
- Searching for the Impact of Active Galactic Nuclei in Galaxy Quenching
- Time: 3:30 pm - 4:30 pm
- Place: 4421 Sterling Hall
- Speaker: Prof. Decker French, The University of Illinois at Urban-Champaign
- Abstract: AGN feedback is expected to have a key role in the evolution of galaxies, especially as galaxies evolve from star-forming to quiescent. However, direct connections between observations of AGN activity and the quenching of galaxies have been difficult. AGN vary on all timescales, with complete duty cycles more rapid than the timescales to observe evolutionary trends in galaxies. Wide-field spectroscopic observations provide a key observational constraint on the past AGN histories of galaxies through the detection of extended emission line regions. The effects of past AGN activity can be observed if gas surrounding the galaxy is illuminated by a nuclear source, even if the AGN has faded. Extreme examples of this can be observed as "voorwerps" in broadband imaging, but spectroscopy is needed to find and characterize fainter cases. I will present recent work using MaNGA observations of galaxies in the process of quenching after a starburst (post-starburst galaxies). Using MaNGA observations of multiple post-starburst galaxy samples, we see extended emission line regions due to past AGN activity. These observations allow us to constrain the duty cycle of AGN activity during this transitionary phase of galaxy evolution over a long time baseline of 10^4 - 10^5 years. This intermittent AGN activity may play a role in suppressing star formation, driving low velocity outflows, and removing molecular gas in quenching galaxies.
- Host: Ke Zhang
Friday, October 13th, 2023
- Theory Seminar (High Energy/Cosmology)
- Cosmological gravitational particle production of massive spin-2 particles
- Time: 1:00 pm - 2:00 pm
- Place: Chamberlin 5310
- Speaker: Siyang Ling, Rice University
- Abstract: The phenomenon of cosmological gravitational particle production (CGPP) is expected to occur during the period of inflation and the transition into a hot big bang cosmology. Particles may be produced even if they only couple directly to gravity, and so CGPP provides a natural explanation for the origin of dark matter. In this work we study the gravitational production of massive spin-2 particles assuming two different couplings to matter. We evaluate the full system of mode equations, including the helicity-0 modes, and by solving them numerically we calculate the spectrum and abundance of massive spin-2 particles that result from inflation on a hilltop potential. We conclude that CGPP might provide a viable mechanism for the generation of massive spin-2 particle dark matter during inflation, and we identify the favorable region of parameter space in terms of the spin-2 particle's mass and the reheating temperature. As a secondary product of our work, we identify the conditions under which such theories admit ghost or gradient instabilities, and we thereby derive a generalization of the Higuchi bound to Friedmann-Robertson-Walker (FRW) spacetimes.
- Host: Yoshihiko Abe