Bulletin of the American Physical Society
2021 Annual Meeting of the APS Four Corners Section
Volume 66, Number 11
Friday–Saturday, October 8–9, 2021; Virtual; Mountain Daylight Time
Session D01: Lustig Award Session |
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Chair: Stacy Palen, Weber State University |
Friday, October 8, 2021 1:30PM - 2:00PM |
D01.00001: A Machine Learning Approach Using Gravity and Cosmic Ray Muon Data for Shallow Subsurface Density Prediction at the Showa-Shinzan Lava Dome, Usu, Japan Invited Speaker: Katherine Cosburn Imaging shallow subsurface anomalies at volcanic structures is important for understanding magma transport and hazard monitoring. In recent years, the use of machine learning has gained increasing attention for solving complex inversion problems, particularly within the field of seismology. Here we present a physics-based, machine learning method for imaging static density variations at the Showa-Shinzan lava dome in Japan. We generate synthetic cosmic-ray muon and gravity datasets using theoretical knowledge of the forward kernels, which we use to train a machine learning (ML) algorithm to interpret subsurface density anomalies. The accuracy of our trained ML algorithm is determined by comparing against the known forward calculation and we validate our model on previously published gravity and muography data from the Showa Shinzan lava dome, which we then compare methodologies with a more traditional inversion. Our work thus far has focused on static imaging, however, we explore the feasibility of the ML algorithm for generating a time series of images if given time-varying geophysical observations. Another advantage of using a (supervised) physics-based approach is its applicability to a range of observables, such as seismic travel times and electrical conductivity. [Preview Abstract] |
Friday, October 8, 2021 2:00PM - 2:30PM |
D01.00002: Second-harmonic generation and the conservation of spatiotemporal orbital angular momentum of light Invited Speaker: Guan Gui Light with spatiotemporal orbital angular momentum (ST-OAM) is a recently discovered type of structured and localized electromagnetic field. This field carries characteristic space--time spiral phase structure and transverse intrinsic OAM. Here, we present the generation and characterization of the second harmonic of ST-OAM pulses. We uncover the conservation of transverse OAM in a second-harmonic generation process, where the space--time topological charge of the fundamental field is doubled along with the optical frequency. Our experiment thus suggests a general ST-OAM nonlinear scaling rule, analogous to that in conventional OAM of light. Furthermore, we observe that the topology of a second-harmonic ST-OAM pulse can be modified by complex spatiotemporal astigmatism, giving rise to multiple phase singularities separated in space and time, depending on group velocity mismatch or phase mismatch. We also analyzed the spatiotemporal momentum density and energy density flows of a fundamental ST-OAM pulse and its second-harmonic field. Our study opens a new route for nonlinear conversion and scaling of light carrying ST-OAM, with the potential for driving other secondary ST-OAM sources in electromagnetic, thermoacoustic, electron waves and beyond. [Preview Abstract] |
Friday, October 8, 2021 2:30PM - 3:00PM |
D01.00003: Neutrinos and quantum fields in the Universe Invited Speaker: Mainak Mukhopadhyay A core-collapse supernova (CCSN) serves as nature’s own laboratory. In this talk, I will discuss how neutrinos from various phases of a CCSN can be used to gain insights and understanding in the broader context. I will focus on my work on localizing a progenitor prior to collapse using pre-supernova neutrinos. Hours before a nearby star, like Betelgeuse, becomes a supernova, a modern neutrino detector will record $\sim 200$ neutrino inverse beta decay interactions. Their topology can give the direction to the star with an error of $\sim 60^\circ$. This allows to narrow the list of potential stellar candidates to less than ten, thus facilitating astronomy searches and act as an early-warning system. Next, I will talk about my work in multi-messenger astronomy which involves combining supernova neutrino observations with gravitational wave (GW) observations. When a burst of neutrinos from a CCSN passes by the Earth, it causes a permanent change in the local space-time metric, called the gravitational memory. Long considered unobservable, this effect will be detectable in the near future, for a galactic supernova, at deci-Hertz GW interferometers. I will discuss the physics potential of these next generation GW detectors like DECIGO and BBO to observe the neutrino memory effect in the context of multimessenger astronomy and for tests of gravity. [Preview Abstract] |
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