Aspen Center for Physics

2021 Colloquia

Thursdays at 3 p.m. MDT, 9 p.m. UTC

via Zoom

Click Here To Access the Talks



  • June 3, 2021
    Dynamical Tests of Dark Matter in the Milky Way
    Speaker: Robyn Sanderson,  University of Pennsylvania, Flatiron Institute
    The results of the Gaia astrometric mission have ushered in a new era of "precision Galactic dynamics". Using this new phase-space map of Galactic stars with unprecedented volume and accuracy, we are beginning to obtain new insights into the dark matter distribution in our Galaxy as well as its formation history. Thanks to significant advances on the computational front, meanwhile, we can now compare these insights directly with, and test our modeling strategies on, simulations of Milky-Way-mass galaxies where the influence of baryons and the cosmological context on the dark matter structure are realistically taken into account. I will demonstrate how this convergence of new data and better models improves our understanding of the Milky Way's dark matter distribution, leading to better constraints on the nature of dark matter.
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  • June 10, 2021
    Atmospheric Dynamics of Hot-Jupiters
    Speaker: James Cho, Flatiron Institute
    Close-in “hot planets” present a new opportunity for enriching our understanding of atmospheric dynamics of all planets. Not only are they presently the most well observed exoplanets, subject to an unusual forcing arrangement (i.e., steady irradiation on the same side of the planet throughout its orbit, leading to “perpetual day and night sides”), the dynamics on these planets is also unlike that on any of the solar system planets. Moreover, characterizing the flow pattern and temperature distribution on the extrasolar planets is critical for reliable interpretation of data currently being collected, as well as of data from large missions soon to come online (e.g., JWST and Ariel). In this talk, the flow structures (e.g., storms and jets) and the variability they induce on a large class of exoplanets, known as “hot-Jupiters”, will be discussed.
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  • June 17, 2021
    Modeling the Within Host Dynamics of SARS-CoV-2 Infection
    Speaker: Alan S Perelson, Los Alamos National Laboratory
    SARS-CoV-2 has infected more than 170 million people and caused more than 3.5 million deaths.  Mathematical modeling of the infection dynamics within individual hosts can provide quantitative information about disease pathogenesis and host-viral interactions.  Here I will discuss recent modeling work involving simple target cell-limited models and then more complex models with innate immune responses, models involving both upper and lower respiratory tract infection, and models of the effects of antiviral agents given either prophylactically or as treatment. If time permits, I will also discuss a mechanistic model that aims to relate the amount of virus in the upper respiratory tract to the probability of transmitting the virus to another person during a contact, and how this then relates to issues of importance in epidemiology.
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  • June 24, 2021
    Searching for Massive Black Holes in Dwarf Galaxies
    Speaker: Vivienne Baldassare, Washington State University
    The present-day population of supermassive black holes in low-mass galaxies offers a window into massive black hole formation in the early universe. While we cannot yet observe the formation of "black hole seeds" at high redshift, the fraction of small galaxies that host a massive black hole -- and the properties of those black holes -- are thought to depend on the mechanism by which they form. However, black holes in the smallest galaxies can be difficult to find, requiring creative new approaches. I will present recent work showing that long-term optical photometric variability in low-mass galaxies can identify active galactic nuclei that are missed by other selection techniques. I will also discuss implications for black hole formation and future opportunities for progress with upcoming surveys and facilities.
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  • July 1, 2021
    Measuring the Radii of Neutron Stars
    Speaker: Coleman Miller, University of Maryland
  • The last few years have seen remarkable progress in astronomical measurements of neutron stars that have bearing on the properties of matter beyond nuclear saturation density.  These measurements include the gravitational-wave constraint on tidal deformability from the double neutron star coalescence GW170817, and measurements of the radii of two neutron stars of significantly different masses (PSR J0030+0451 at ~1.4 solar masses, using data from the NICER X-ray telescope, and PSR J0740+6620 at ~2.1 solar masses, using a combination of NICER, XMM-Newton, and radio data).  I will discuss these results and their implications, with a particular focus on the methods used to obtain radii from X-ray measurements, including an evaluation of possible systematic errors.
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  • July 8, 2021
    Topological Quantum Computation with Majorana Zero Modes
    Speaker: Roman Lutchyn, Microsoft Station Q
  • Research in quantum computing has offered many new physical insights and a potential to exponentially increase the computational power that can be harnessed to solve important problems in science and technology. The largest fundamental barrier to building a scalable quantum computer is errors caused by decoherence. Topological quantum computing overcomes this barrier by exploiting topological materials which, by their nature, limit errors. In this colloquium I will discuss how to engineer topological superconductors at the interface of a conventional superconductor and a semiconductor with spin-orbit interaction. I will discuss recent experiments aiming to detect Majorana zero-energy modes at the ends of the proximitized nanowires. Finally, I will present designs for scalable quantum computers composed of qubits involving superconducting islands in a Coulomb blockade regime hosting aggregates of four or more Majorana zero modes.
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  • July 15, 2021
    The Universe from a Single Particle
    Speaker: Michael Freedman, Microsoft Station Q
    This talk derives from a mathematical look at the foundations of quantum mechanics and attempts a “creation story”. It is based on joint work with Modj Shokrian Zini, arXiv:2011.05917. The purest question “Why is there something instead of nothing?” seems out of reach; we, instead, attempt an answer to: “Why does there appear to be a multitude of things?” In more technical language we propose that spontaneous symmetry breaking (SSB), not on the usual level of states but rather on the level of (probability distributions on Hamiltonian) operators, can “break” single particle quantum mechanics into interacting physics. I will speculate at then end on how this story may eventually dovetail with the more famous creation stories: string theory and ADS/CFT.
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  • July 22, 2021
    Supernovae Ignited by Nuclear Fission: The Aspen Primer
    Speaker: Charles Horowitz,  Indiana University
  • Type 1A supernovae (SN Ia) are giant stellar explosions that are important distance indicators in cosmology.  Presently there is tension between Hubble constant values determined from SN and other means.  SN Ia are thought to involve white dwarf stars, but it is unclear how they explode.  We propose a new mechanism involving a natural nuclear fission explosion.  White dwarfs cool and eventually crystalize.   Our molecular dynamics simulations find that the first solids to form, as the star cools, are greatly enriched in actinides such as uranium.  This is because actinides have the highest nuclear charge.  These solids may support a fission chain reaction that, in turn, could ignite carbon fusion and explode the star.  This physics parallels that in terrestrial nuclear weapons. 
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  • July 29, 2021
    The Measurement Induced Phase Transition in Open Quantum Many-Body Systems
    Speaker: Jedediah Pixley, Rutgers University
  • The ability to control and measure properties of quantum many-body systems has reached an unprecedented level of experimental accuracy. The dynamical states that emerge in these systems can be theoretically characterized by their entanglement structure. Generically, the unitary time evolution of a quantum many-body system couples its microscopic constituents leading to a highly entangled quantum state. On the other hand, performing a global measurement to learn something about the physical content of the system will collapse the wavefunction, destroying any entanglement. However, if a quantum system undergoing unitary time evolution is measured locally at a small but non-zero rate, it was recently discovered that the highly entangled state survives. Only after a critical measurement rate will the wavefunction essentially collapse leading to a measurement induced phase transition in the structure of the entanglement. This talk will discuss the recent progress in our understanding of this measurement induced phase transition in a wide array of open quantum many body systems.  Focusing on a chain of qubits we demonstrate that this transition belongs to a novel universality class that is described by a non-unitary conformal field theory with multifractal correlations in space-time.
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  • August 5, 2021
    The Naturally Unnatural Standard Model of Particle Physics
    Speaker: Nausheen Shah, Wayne State University
  • The Standard Model (SM) of Particle Physics provides an excellent description of nature. However, it is very much an empirical model: Why are there 3 generations of matter with such large mass hierarchies? What is the origin of their mixings? What is dark matter (DM)? What dynamics govern the Higgs mechanism? If Ultraviolet symmetry breaking governs the structure we observe at the weak scale, apparent fine-tunings may be a hint of the global structure dictating beyond the SM physics. In this talk I will discuss some fine-tunings that may be responsible for the structure we observe in Higgs couplings, fermion masses and mixings, and possible connections of the Higgs sector with DM 
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  • August 12, 2021
    Searching for New Particles in the Sky
    Speaker: Maria Baryakhtar, New York University

    Theories that seek to explain the outstanding puzzles of the Standard Model of particle physics often predict new, light, feebly-interacting particles whose discovery requires novel search strategies. Perhaps the most motivated of these particles is the QCD axion, which can elegantly solve the outstanding strong-CP problem of the Standard Model; cousins of the QCD axion can also appear, and are natural dark matter candidates.  In light of these particles' small masses and weak interactions, we turn to the sky for clues of their existence. We will see how extreme astrophysical environments --- from our Sun to neutron stars to black holes --- produce large numbers of axions which lead to indirect signatures, or can be directly measured in the lab. I will discuss how rotating black holes source exponentially large numbers of gravitationally-bound axions, creating nature's laboratories for ultralight particles. These systems emit gravitational waves, allowing observatories such as LIGO to search for new particles. If the axions interact with one another, black holes instead turn into axionic beacons, populating the universe with axion waves.
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  • August 19, 2021
    Extracting Dynamics in Quantum Field Theory from Conformal Field Theory Data
    Speaker: Andrew Liam Fitzpatrick, Boston University
  • A compelling view of Quantum Field Theories (QFTs) is that they are points along the RG flow between fixed points described by Conformal Field Theories (CFTs), which in turn are fully characterized by a discrete set of "CFT data".  In this talk, we describe how this picture can be turned into a useful calculational tool for studying QFT at strong coupling in infinite volume in the continuum limit, by applying a variational method motivated by the conformal structure of the ultraviolet CFT fixed point of the theory.  We demonstrate how dynamical quantities can be obtained, including energy eigenvalue statistics, Lorentzian correlation functions, and the evolution of excited states.
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  • August 26, 2021
    Machine Learning Quantum Emergence
    Speaker: Eun-Ah Kim, Cornell University
  • Decades of efforts in improving computing power and experimental instrumentation were driven by our desire to better understand the complex problem of quantum emergence. The resulting "data revolution" presents new challenges. I will discuss how these challenges can be embraced and turned into opportunities through machine learning. The scientific questions in the field of electronic quantum matter require fundamentally new approaches to data science for two reasons: (1) quantum mechanics restricts our access to information, (2) inference from data should be subject to fundamental laws of physics. Hence machine learning quantum emergence requires collective wisdom of data science and condensed matter physics. I will review rapidly developing efforts by the community in using machine learning to solve problems and gain new insight. I will then present my group’s results on the machine-learning-based analysis of complex experimental data on quantum matter.
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  • September 2, 2021
    NoTORIous Neutrinos
    Speaker: Mu-Chun Chen, University of California Irvine
  • The discovery of non-zero neutrino masses has provided arguably the most compelling evidence for Physics beyond the Standard Model. Their observed small masses hint at Physics at a very high energy scale, and thus offers a unique window into the theory that underlies the Standard Model of Particle Physics. In this talk, I will describe how the pattern of neutrino masses may be closely connected to the intricate mathematics of modular symmetries.


  • September 9, 2021
    Searching for New Physics in the Universe's Oldest Light
    Speaker: Colin Hill, Columbia University and Flatiron Institute
    I will discuss recent and ongoing work focused on attempts to restore concordance amongst cosmological data sets, motivated by discrepancies amongst some probes of the cosmic expansion rate (H0) and the matter clustering amplitude (S8).  Particular attention will be paid to models invoking new physics at or prior to recombination, including small-scale baryon-clumping models (e.g., due to primordial magnetic fields) and quasi-accelerating early dark energy models.  In particular, I will discuss constraints on these scenarios derived using the latest data from the Atacama Cosmology Telescope (ACT).  I will conclude with a look ahead to forthcoming CMB measurements from ACT, which will provide a powerful test of these models in the low-noise, high-resolution regime.

  • September 16, 2021
    Gravitational-wave Detection, Macroscopic Quantum Mechanics and Quantum Gravity in the Lab
    Speaker: Yanbei Chen, Caltech
  • Experimental progress in quantum optomechanics has allowed preparing, manipulating, and probing the mechanical motions of macroscopic objects in the quantum regime.  For example, laser interferometer gravitational-wave detectors are now sensitive to displacements of kg-scale test masses near the free-mass Standard Quantum Limit, which arises from applying the Heisenberg Uncertainty Principle to kg-scale test masses.  Upcoming and future upgrades of these interferometers will benefit from techniques that substantially surpass the Standard Quantum Limit.  Quantum optomechanics also provides new opportunities for testing quantum mechanics, quantum measurement theory, and possibly studying the quantum nature of gravity. If these tests confirm conventional predictions, we will demonstrate the validity of quantum mechanics in unprecedented regimes.  Deviations from conventional predictions will lead to new physics.