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Events on Thursday, April 4th, 2024

NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Tuning into Cosmic Neutrinos at the Highest Energies
Time: 9:00 am - 10:00 am
Place: 5280 Chamberlin Hall
Speaker: Stephanie Wissel, Penn State
Abstract: Neutrinos are powerful probes of both astrophysics and fundamental particle physics at the highest energies. Weakly interacting and uncharged, they propagate undeterred and unabsorbed through the universe. In the last decade, we have observed a flux of high-energy (TeV-scale) neutrinos and through a multi-messenger lens — the combined observations of neutrinos and other messengers like photons — we are starting to see hints of energetic neutrino sources for the first time. At higher energies still, beyond the PeV scale, we can probe the most energetic sources of both neutrinos and cosmic rays, but current neutrino experiments become too small to observe a sizable flux. With long propagation lengths in both ice and air, radio detection offers an attractive solution to building the gigaton-scale detectors needed by allowing us to build sparse detectors sensitive to neutrinos over hundreds of kilometers. In this talk, I will review the landscape of current radio neutrino experiments and how next generation detectors can lead to new discoveries. I will also present my vision for the future of the Wisconsin IceCube Particle Astrophysics Center.
Host: Francis Halzen
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R. G. Herb Condensed Matter Seminar
Quantum materials through the nano-lens: surprises beyond the diffraction limit
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Alexander McLeod, UMN
Abstract: Toolsets wielded by condensed matter researchers in the past century have expanded enormously into frontiers of the ultra-small and ultra-fast, today leveraging advancements like atomically precise crystal growth, nano-scale device assembly, and femtosecond spectroscopy with ultrafast photon pulses. On the other hand, despite breathtaking 20th century advancements in photon sources and detection technologies, our capacity to resolve condensed matter by optical spectroscopies has remained largely arrested by the diffraction limit since its 19th century observation by Ernst Abbe. However, recent decades have seen the marriage of “conventional” optics with scanning probes to circumvent the diffraction limit, realizing a nanometer-resolved optical spectroscopy mediated fundamentally by electromagnetic near-fields. In this seminar, I review and celebrate the breakthrough of this technique into the temperature and spatial scales relevant to fundamental studies of quantum materials. I showcase seminal investigations of collective excitations in 2-dimensional media like graphene, electronic phase competition in correlated electron solids including transition metal oxides, and on-demand control of optical properties in strongly interacting materials. I will share my perspectives for the future of nano-spectroscopy of quantum materials, a future that is simultaneously ultra-bright and ultra-small, and fundamentally transformative for the study of complex matter at nanometer scales.
Host: Alex Levchenko
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Thesis Defense
The Cosmic Symphony: Magnetic Fields and Turbulence Across Clouds, Galaxies, to Galaxy Clusters
Time: 11:00 am
Place: 5280 Chamberlin
Speaker: Yue Hu, Physics Graduate Student
Abstract: Turbulence and magnetic fields stand at the crossroads of astrophysical and cosmological inquiry, bridging microscopic physics, such as cosmic rays, to the large-scale galaxy cluster evolution. Despite their paramount importance, a thorough understanding of their characteristics has remained elusive. In this thesis, I explore the properties of magnetohydrodynamic (MHD) turbulence within a partially ionized medium through 3D MHD simulations of two-fluids (ions and neutrals), as well as the influence of stellar feedback. Furthermore, mapping the 3D magnetic field in spatial three dimensions has posed a century-long challenge. In this thesis, based on the anisotropic properties of MHD turbulence, I introduce three innovative techniques for tracing the 3D magnetic field: the Velocity Gradient Technique and the use of Convolutional Neural Networks. I will illustrate how these advancements in 3D magnetic field mapping significantly enhance our comprehension of star formation, Galactic magnetic fields, the CMB foreground polarization, Seyfert activities in nearby galaxies, and the evolution of galaxy clusters.
Host: Alex Lazarian
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Multi-wavelength emission from Jets of nearby radio galaxies
Time: 2:30 pm - 3:30 pm
Place: CH 5280
Speaker: Riku Kuze, Tohoku University
Abstract: Relativistic jets in radio galaxies emit multi-wavelength photons, indicating the existence of nonthermal particles. However, the origin of these nonthermal particles is unknown. One plausible scenario is the electron-positron pair production via the two-photon interaction using the gamma rays produced by magnetic reconnection in the black-hole magnetosphere. This scenario is possible if the accretion flow is in a highly magnetized state, i.e., magnetically arrested disk (MAD) state. We construct the multi-wavelength photon emission model based on this scenario. In this talk, we will show the results of applying our model to M87. We calculate emissions from jets and MADs and compare the model prediction to the simultaneous multi-wavelength observational data for M87. We find that the emission from jets explains the optical to the X-ray data, and that from MADs explains the gamma-ray data. We also estimate the neutrino emission from jets and MADs, and we find that the neutrino luminosity is too low to observe by the IceCube Gen-2.
Host: Ke Fang
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Astronomy Colloquium
Time: 3:30 pm - 4:30 pm
Place: 4421 Sterling Hall
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