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Events During the Week of November 14th through November 20th, 2021

Monday, November 15th, 2021

No events scheduled

Tuesday, November 16th, 2021

Network in Neutrinos, Nuclear Astrophysics, and Symmetries (N3AS) Seminar
The fate of twin stars on the unstable branch
Time: 2:00 pm
Place: Meeting ID: 994 6425 2867
Speaker: Pedro Espino, University of California, Berkeley and Pennsylvania State University
Abstract: Hybrid hadron-quark equations of state that give rise to a third family of stable compact stars have been shown to be compatible with the LIGO-Virgo event GW170817. Stable configurations in the third family are called hybrid hadron-quark stars. The equilibrium stable hybrid hadron-quark star branch is separated by the stable neutron star branch with a branch of unstable hybrid hadron-quark stars. The end-state of these unstable configurations has not been studied, yet, and it could have implications for the formation and existence of twin stars — hybrid stars with the same mass as neutron stars but different radii. We modify existing hybrid hadron-quark equations of state with a first-order phase transition in order to guarantee a well-posed initial value problem of the equations of general relativistic hydrodynamics, and study the dynamics of non-rotating or rotating unstable twin stars via 3-dimensional simulations in full general relativity. We find that unstable twin stars naturally migrate toward the hadronic branch. Before settling into the hadronic regime, these stars undergo (quasi)radial oscillations on a dynamical timescale while the core bounces between the two phases. Our study suggests that it may be difficult to form stable twin stars if the phase transition is sustained over a large jump in energy density, and hence it may be more likely that astrophysical hybrid hadron-quark stars have masses above the twin star regime. We also study the minimum-mass instability for hybrid stars, and find that these configurations do not explode, unlike the minimum-mass instability for neutron stars. Additionally, our results suggest that oscillations between the hadronic and quark phases could provide gravitational wave signals associated with such phase transitions in core-collapse supernovae and white dwarf-neutron star mergers. Meeting ID: 994 6425 2867
Host: Baha Balantekin
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Wednesday, November 17th, 2021

Theory Seminar (High Energy/Cosmology)
No Page curves for the de Sitter horizon
Time: 1:00 pm
Place: Chamberlin 5280
Speaker: Evita Verheijden, University of Amsterdam
Abstract: One of the greatest puzzles in our universe, which can -- to good approximation -- be described by de Sitter space, is a proper understanding of the cosmological horizon that surrounds any observer. Over the past few years, a semi-classical approach involving quantum extremal surfaces and so-called ‘islands’ has been very successful to increase our understanding of the black hole information problem; in light of these advancements, it could prove fruitful to undertake a similar approach to investigate an evaporating de Sitter horizon. In this talk I will consider such an approach for two-dimensional de Sitter space. Starting from three-dimensional de Sitter space, I will show how a partial dimensional reduction supplies 2D JT de Sitter with an auxiliary system acting as a heat bath. I will then contrast the time-dependent entropy of radiation collected by an observer at future infinity with that collected by an observer inside the static patch. Central to the analysis in the static patch is the identification of a weakly-coupled region close to the cosmological horizon. I will highlight how backreaction considerations crucially obstruct both observers from witnessing unitary evaporation.
Host: Lars Aalsma
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Thursday, November 18th, 2021

Astronomy Colloquium
Testing Galaxy Formation Models with Large-scale Surveys of the Milky Way Stellar Halo
Time: 3:30 pm
Place: 4421 Sterling Hall, Coffee and Cookies at 3:30 pm, Talk starts at 3:45 pm
Speaker: Emily Cunningham, Flatiron Research Fellow, Center for Computational Astrophysics
Abstract: While the vast majority of the light from our galaxy comes from the Galactic disk, the vast majority of the mass of the Milky Way (MW) is in its dark matter halo. Because we cannot directly observe the MW's dark matter halo, we must use luminous tracer populations to study the mass distribution indirectly. Fortunately, there are stars strewn throughout the MW's dark matter halo. According to the hierarchical paradigm for galaxy evolution, the MW built up its halo of dark matter over cosmic time by accreting smaller dwarf galaxies. The remnants of these accreted dwarfs make up the MW's stellar halo. Halo stars can therefore be used both to constrain the dark matter distribution of the MW as well as inform us about the dwarf galaxies in which they formed. I will present my ongoing theoretical and observational work using halo stars to map the dark matter distribution and disequilibrium in the MW, as well as study the faint, low-mass galaxies that were consumed by the MW during its formation. I will discuss the crucial roles of current and upcoming large-scale surveys of the MW halo for addressing fundamental questions in galaxy formation.

We strongly encourage you to attend the colloquium in person. If that is impossible, it is available over zoom at the following link:

Host: Elena D'ONghia
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Friday, November 19th, 2021

Graduate Introductory Seminar (Physics 701)
Cosmic neutrinos with IceCube - results and future steps.
Time: 12:05 pm
Place: 2241 Chamberlin
Speaker: Albrecht Karle, UW Madison Department of Physics
Host: Sridhara Dasu
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Physics Department Colloquium
Scaling down the laws of thermodynamics
Time: 3:30 pm
Place: 2103 Chamberlin Hall
Speaker: Christopher Jarzynski, UMD
Abstract: Thermodynamics provides a robust conceptual framework and set of laws that govern the exchange of energy and matter. Although these laws were originally articulated for macroscopic objects, nanoscale systems also exhibit “thermodynamic¬-like” behavior – for instance, biomolecular motors convert chemical fuel into mechanical work, and single molecules exhibit hysteresis when manipulated using optical tweezers. To what extent can the laws of thermodynamics be scaled down to apply to individual microscopic systems, and what new features emerge at the nanoscale? I will describe some of the challenges and recent progress – both theoretical and experimental – associated with addressing these questions. Along the way, my talk will touch on non-equilibrium fluctuations, “violations” of the second law, the thermodynamic arrow of time, nanoscale feedback control, strong system-environment coupling, and quantum thermodynamics.
Host: Alex Levchenko
Presentation: Jarzynski-title+abstract.pdf
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