Asymptotics in Astrophysics Seminar
4 events
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Seminar
Asymptotic gravity waves in core-collapse progenitor stars
October 22 (Wed) 16:30 - 17:30, 2025
Lucy McNeill (Hakubi Assistant Professor, The Hakubi Center for Advanced Research, Kyoto University)
Internal gravity waves (IGW) are generically excited at convective boundaries inside stars. During the final months before a massive stars’ core-collapse, the excited IGW carry energy and angular momentum so large that the wave transport can e.g. completely set the rotation period of the neutron star remnant. In this talk, I present the first three-dimensional simulation of a core-collapse progenitor with which we can characterise IGW generation and transport preceding core-collapse. First I will show that the energy carried by convectively generated IGW in our simulation is described remarkably well by the established asymptotic theory, which utilizes e.g. the WKB approximation. But, the IGW’s subsequent propagation and dissipation depends very sensitively on the rotation. And in 3D, the equilibrium rotation patterns that develop are too complex to be captured in the established asymptotic theory for wave transport. I will present the rich nonlinear wave dynamics in our 3D simulation responsible for angular momentum transport and wave dissipation. I will propose that the angular momentum transport is governed by a “mean flow” interaction between global rotation and IGW transport. Mean flow interactions can explain the periodic Easterly <-> Westerly sudden reversal of winds at the equator on Earth, Saturn and Jupiter. If such reversals are realised in massive stars, it has implications for several exotic phenomena. This includes IGW driven mass loss outbursts observed in the final months before core-collapse supernova, and also gamma ray burst progenitor stars - which require very extreme rotation at core collapse.
Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359
Event Official Language: English
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Seminar
Non-perturbative formulation of resonant quantum mechanics within unified exact WKB framework
May 28 (Wed) 16:00 - 17:30, 2025
Okuto Morikawa (Special Postdoctoral Researcher, Division of Fundamental Mathematical Science, RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS))
We study quasi-stationary states in quantum mechanics using the exact WKB analysis as a non-perturbative framework. We explore unstable states such as resonances by analyzing the inverted Rosen-Morse potential, which exhibits barrier resonance. This model allows exact solutions, enabling a direct comparison with exact WKB predictions. We provide a simple analytic picture of resonance and demonstrate consistency between exact and WKB-based results. A unified exact WKB framework is developed for exploring the equivalence and complementarity of different well-established regularizations \`a la Zel'dovich, complex scaling, and rigged Hilbert space within this framework.
Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359
Event Official Language: English
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Seminar
Asymptotic Waves in Stars
April 23 (Wed) 14:00 - 15:30, 2025
Jim Fuller (Professor, Division of Physics, Mathematics, and Astronomy (TAPIR), California Institute of Technology (Caltech), USA)
Waves propagating through stars often have very short wavelengths in the radial direction, enabling WKB approximations that facilitate understanding. The main types of waves that propagate in stars are acoustic waves (restored by pressure forces) and gravity waves (restored by buoyancy forces). I will also discuss how the properties of these waves are changed by rotation (adding Coriolis and centrifugal forces) and magnetic fields (adding Lorentz forces). Finally, I will discuss how these waves carry energy and angular momentum through stars, and discuss some potential consequences for stellar evolution.
Venue: Hybrid Format (3F #359 and Zoom), Seminar Room #359
Event Official Language: English
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Seminar
asymptotics in astrophysics SG session 4: helioseismology
November 29 (Fri) 10:30 - 12:00, 2024
Ryota Shimada (Ph.D. Student, Department of Astronomy, Graduate School of Science, Kyoto University)
Constraining the distribution of internal magnetic fields through observations is considered to advance solar dynamo models aimed at understanding the 11-year cycle of solar magnetic activity. This paper [1] is on the frequency shift of standing acoustic waves inside the Sun caused by internal magnetic fields. Quasi-degenerate perturbation theory is applied to treat perturbation by magnetic fields. I’d like to discuss their methods and application in the session.
Venue: Seminar Room #359 / via Zoom
Event Official Language: English
4 events