Events at Physics |
Events During the Week of April 24th through May 1st, 2022
Monday, April 25th, 2022
- No events scheduled
Tuesday, April 26th, 2022
- Thesis Defense
- Hunting for cosmic neutrino sources from Giga- to Exa-electronvolt with IceCube
- Time: 2:00 pm
- Place: B343 Sterling
- Speaker: Alex Pizzuto, Physics PhD Graduate Student
- Abstract: Ever since the first observation of cosmic rays over a century ago, the origins of these high-energy particles has remained a mystery. Identifying and understanding the sources of these cosmic rays could provide invaluable insight into not only astrophysics but also fundamental particle physics. The IceCube Neutrino Observatory, a cubic-kilometer neutrino telescope instrumented at the geographic South Pole, has made remarkable progress on this front -- first with the detection of a diffuse astrophysical neutrino flux in 2013, and later with the identification of a particular flaring blazar as a promising neutrino source. However, the sources of the vast majority of the diffuse neutrino flux remain unidentified. The goal of this thesis is to identify astrophysical neutrino sources despite our limited detection threshold. We show how analyzing neutrino data with new techniques can reveal an immense deal about the nature of the universe's most energetic particle accelerators. After providing a description of the state of the field and a quick overview of the general analysis techniques used, we present a variety of analyses focused on searching for neutrino emission from promising classes of astrophysical transients. Although all of these analyses resulted in non-detections, we are hopeful that the tools presented here will assist with the identification of cosmic neutrino sources in the years to come.
- Host: Justin Vandenbroucke
- Theory Seminar (High Energy/Cosmology)
- Euclidean Wormholes: Conceptual Issues and Applications
- Time: 4:00 pm
- Place: Chamberlin 5280
- Speaker: Pablo Soler Gomis, CTPU - Institute for Basic Science
- Abstract: An important open question in the study of quantum gravity is whether topologically non trivial spacetime configurations (Euclidean wormholes) should be taken into account in the path integral. If present, they can generate phenomenologically relevant couplings and play an important role, e.g. in breaking axionic shift symmetries. At the same time, they pose deep conceptual problems such as the appearance of random couplings in the effective action or conflicts with holography. I will introduce in this talk some of the basic features of Euclidean wormholes and their phenomenological applications, focusing in particular on axionic wormholes and the role played by (massive) dilatons in their construction.
- Host: George Wojcik
- Network in Neutrinos, Nuclear Astrophysics, and Symmetries (N3AS) Seminar
- From SNe to SNRs: Hunting Legacies of Supernova Explosions in Supernova Remnants
- Time: 6:00 pm - 7:00 pm
- Place: virtual - Join Zoom Meeting Meeting ID: 912 3071 4547
- Speaker: Hiro Nagataki, RIKEN ABBL
- Abstract: Progress of theories for core-collapse supernovae is remarkable, including developments of multi-dimensional hydro simulations. Observational confirmations are mandatory to understand the explosion mechanism of core-collapse supernovae completely. Direct observations will be done by neutrinos and gravitational waves for a future supernova that will happen in Milky Way or very nearby galaxies. Such a nearby supernova should occur in the future, but the supernova rate is roughly 1 event per century per galaxy. The youngest supernova found in Milky Way is Cassiopeia A, whose age is about 350 yrs old. The youngest supernova in Large Magellanic Cloud is SN1987A which is 35 yrs old. Therefore, we cannot predict when the next nearby supernova will happen. In this talk, I would like to present our unique approach to finding observational evidence of the explosion mechanism of core-collapse supernovae in young supernova remnants. We did 3-dimensional hydro simulations that covered from supernova explosion phase to the supernova remnant phase. Such multi-D simulations with a wide range of scales (in time and length) have never been done before. We could demonstrate that such simulations are possible thanks to excellent international collaborations. This talk will mainly present a detailed comparison between our simulations and SN1987A. I will shortly show that such comparison is meaningful for Cassiopeia A and Type Ia supernova remnants, too. Join Zoom Meeting Meeting ID: 912 3071 4547
- Host: Baha Balantekin
Wednesday, April 27th, 2022
- Physics ∩ ML Seminar
- Quantum field theory and deep neural networks
- Time: 11:00 am - 12:15 pm
- Place: Chamberlin 5280 (Zoom link for those attending online: )
- Speaker: Ro Jefferson, Nordita
- Abstract: Recently, exciting progress has been made in the study of deep neural networks (DNNs) by applying ideas and techniques from physics, and in particular QFT. In this talk, I will first give a brief overview of some key aspects of the approach to DNNs from effective theory, and highlight the information-theoretic language that unites these two seemingly disparate fields. Then, I will explain how one can go beyond the level of analogy by explicitly constructing a bona-fide QFT corresponding to a general class of DNNs encompassing both recurrent and feedforward architectures. The resulting theory closely resembles the well-studied O(N) vector model, in which the variance of the weight initializations plays the role of the 't Hooft coupling. In this framework, the Gaussian process approximation used in machine learning corresponds to a free field theory, and finite-width effects can be computed perturbatively in the ratio of depth to width, T/N. These provide corrections to the correlation length that controls the depth to which information can propagate through the network, and thereby sets the scale at which such networks are trainable by gradient descent. This analysis provides a first-principles approach to the rapidly emerging NN-QFT correspondence, and opens several interesting avenues to the study of criticality in deep neural networks. Based on 2109.13247 with Kevin T. Grosvenor.
- Host: Gary Shiu
Thursday, April 28th, 2022
- R. G. Herb Condensed Matter Seminar
- Few-layer MoTe2: an Unconventional, Ferroelectric Superconductor
- Time: 10:00 am - 11:00 am
- Place: 5310 Chamberlin Hall
- Speaker: Prof. Daniel Rhodes, UW-Madison Dept. of Materials Science and Engineering
- Abstract: Two dimensional materials are layered materials that may be readily exfoliated down to a single atomic layer, presenting an opportunity to noninvasively, and efficiently, control electrical and magnetic ordering, as well as topology. In this talk, I discuss how topology emerges from the bulk, down to the monolayer and how the influence of an electrostatic gate allows us to identify a unique superconducting state in few-layer Td-MoTe2. First, I will discuss how in the clean limit the superconducting transition temperature is enhanced by a factor of 60x, as compared to bulk, in monolayer Td-MoTe2, while still retaining a low carrier density (~1013/cm2), and a density of states that is comparable to the bulk. I will show how the crystal structure factors into the behavior of the superconducting state under external in-plane magnetic fields and how this can be used to quantify of the spin-orbit coupling, an important factor for determining topology and realizing topological superconducting states. After discussion of the monolayer, I will show that this enhancement remains in bilayer MoTe2, despite the change in symmetry. Strangely, our results indicate that superconductivity in bilayer MoTe2 is much more tunable by an electrostatic gate than that of monolayer MoTe2. Not only, we will show that due to the stacking of two layers as compared to one, a ferroelectric switching is allowed - demonstrating the first observation of a 2D ferroelectric superconductor. These findings have profound implications on 2D superconductivity and offer an avenue for future exploration into similarly structured materials.
- Host: Robert McDermott
Friday, April 29th, 2022
- Theory Seminar (High Energy/Cosmology)
- A chiral SU(5) theory with three generations
- Time: 1:00 pm
- Place: Chamberlin 5280
- Speaker: Daniel Stolarski, Carleton University
- Abstract: I will present a study of an interesting strongly coupled chiral quantum field theory. This theory has the same particle content as the simplest grand unified theory of the Standard Model. I will employ tools such as 't Hooft anomaly matching and softly broken supersymmetry to analyze the non-perturbative dynamics of the theory. I will also speculate on the more general lessons of my analysis.
- Host: George Wojcik
- Thesis Defense
- Intensity Mapping: Science and Instrumentation Across the Electromagnetic Spectrum
- Time: 2:00 pm
- Place: B343 Sterling or join online:
- Speaker: Trevor Oxholm, Physics PhD Graduate Student
- Abstract: Line intensity mapping is a growing technique for obtaining tomographic maps of the universe. Line intensity maps feature the integrated emission of a target spectral line from all galaxies within the field of view, making it an unbiased tracer of galaxy emission and a strong tool for galaxy evolution studies. Furthermore, line intensity mapping surveys may probe unprecedented volumes of the universe with modest time requirements, allowing for leading sensitivities of cosmological parameters. In this thesis, I describe modeling efforts for measurements of the intensity mapping signal and for instrumentation developed for the Experiment for Cryogenic Large- aperture Intensity Mapping (EXCLAIM!). EXCLAIM is a pathfinding balloon-borne intensity mapping instrument aiming to map ionized carbon ([CII]) and carbon monoxide (CO) at redshifts 2.5 < z < 3.5 and z < 0.64, respectively. I characterize the target observables in the survey and describe methods for forecasting the performance of the instrument. I apply these forecasting tools to the EXCLAIM survey and to a hypothetical space-based survey, which may be free from the limitations of cosmic variance. The EXCLAIM detectors and optical systems are also described in detail, and with a dual focus on system-level requirements. EXCLAIM features nascent superconducting spectrometer and detector technologies, which must be carefully characterized and modeled before the flight. I describe an operational procedure that may be used to optimize the detectors for an evolving signal, providing a critical advantage for EXCLAIM’s detectors over competing technologies. Finally, the optical system is modeled and shown to comply with system-level mission goals.
- Host: Peter Timbie
- Physics Department Colloquium
- Structural Dynamics in Biology using LCLS
- Time: 3:30 pm
- Place: 2103 Chamberlin Hall
- Speaker: Mark Hunter, SLAC
- Abstract: The resolution revolution of cryo-EM for experimental structure determination of biomacromolecules combined with the breakthrough results of AlphaFold and its derivatives for structure prediction of biomacromolecules have ushered in a new era in structural biology. This poses the question of what is the place for x-ray crystallography and x-ray Free Electron Lasers (xFELs) such as the Linac Coherent Light Source (LCLS) in structural biology moving forward? We believe that one compelling area of research using LCLS is studying the structural dynamics of biomacromolecules. LCLS and other xFELs offer very high temporal resolution combined with atomic spatial resolution while eliminating the ill effects of conventional radiation damage. This unique combination will facilitate the study of both triggered and stochastic biological dynamics. For example, the spatiotemporal resolving power of LCLS can be used to study the initial photophysics and photochemistry in light-sensitive proteins as well as short time points in an enzymatic reaction between a biomacromolecule and substrate. The structural methods can also be combined with powerful complimentary techniques, such as x-ray absorption and emission spectroscopies, to understand the structure and chemical environment of biomacromolecules. The presentation will cover the unique properties of LCLS and the upcoming upgrades to LCLS-II and LCLS-II-HE and how we can use a variety of additional technologies and methodologies to access a myriad of biologically relevant time scales.
- Host: Uwe Bergmann