Past Events

  • Astro Seminar: "Insights Into Dark Matter From the Stellar Halos of Galaxies"

    David Rittenhouse Laboratory, A2

    Robyn Sanderson (Caltech)

    Cosmological simulations can now make specific and detailed predictions for the shapes, masses, and substructure fractions in galactic dark matter halos that depend on the dark matter model assumed. Comparing these predictions to the observed mass distributions of galaxies should in principle lead to constraints on the nature of dark matter, but observable dynamical tracers can be scarce in regions where the dark matter distribution is best able to discriminate between models.

  • 32nd Primakoff Lecture: "Metamaterials and Topological Mechanics"

    David Rittenhouse Laboratory, A8

    Tom Lubensky (University of Pennsylvania)

    Metamaterials are materials engineered to have a property or properties not found in nature, such as a negative optical index of refraction, one-way light or vibration waves, or exotic elastic behavior.  Advances in materials processing, like 3D printing and laser cutting, over the last 10 to 15 years have made it possible to fabricate metamaterials with made-to-order structure at length scales as short as a micron.

  • Astro Seminar: "The Chaotic Life Cycles of Planetary Systems"

    David Rittenhouse Laboratory, A4

    Daniel Tamayo (University of Toronto)

    The past two decades have seen the discovery of thousands of new planetary systems in our galactic neighborhood, many of which look drastically different from our own. However, despite this remarkable observational achievement, we are still struggling to generate theoretical frameworks capable of explaining their divergent evolutionary paths. In particular, a central challenge is modeling the often chaotic orbital evolution of planetary systems over typical lifetimes of billions of years, which sculpts the distribution of orbital architectures that we observe at the present day.

  • HET & HEE Joint Seminar: "Unification from Scattering Amplitudes"

    David Rittenhouse Laboratory, 4N12

    Cliff Cheung (Caltech)

    Scattering amplitudes are fundamental observables that encode the dynamics of interacting particles. In this talk, I describe how to systematically construct these objects without reference to a Lagrangian or an underlying spacetime. The physics of real-world particles like gravitons, gluons, and pions are thus derived from the properties of amplitudes rather than vice versa. Remarkably, the expressions gleaned from this line of attack are marvelously simple, revealing new structures long hidden in plain sight.

  • High Energy Theory Seminar: "Coarse-Graining Holographic Entanglement"

    David Rittenhouse Laboratory, 2N36

    Netta Engelhardt (Princeton)

  • Astro Seminar: "Cosmic Microwave Backlight: Illuminating Large-Scale Structure with the Universe's Oldest Photons"

    David Rittenhouse Laboratory, A2

    Colin Hill (IAS/Flatiron Institute)

    Studies of the cosmic microwave background (CMB) radiation have driven the current era of precision cosmology.  The tightest cosmological constraints to date have been derived from the primary CMB anisotropies, which predominantly probe the universe in its infancy.  However, CMB experiments have recently entered a new regime in which constraints derived from the secondary anisotropies -- sourced by effects between our vantage point and the surface of last scattering -- substantially improve upon those derived from the primary anisotropies alone.

  • Condensed Matter Seminar: "Structure and Topology of Band Structures in the 1651 Magnetic Space Groups"

    David Rittenhouse Laboratory, A4

    Ashvin Vishwanath (Harvard University)

    We describe a powerful theoretical approach to studying electronic band structures, which associates them with elements of a vector space. The set of consistent band structures in a space group can then be expanded in terms of a small set of basis vectors. We calculate the dimension of this vector space, and the necessary electron fillings to obtain band insulators in all magnetic space groups.

  • Astro Seminar: "Moving Mesh Astrophysics"

    David Rittenhouse Laboratory, A4

    Paul Duffel (UC Berkeley)

    Novel methods in recent years have been developed for numerically solving the hydrodynamical and MHD equations relevant to all kinds of astrophysical flows.  I will first (briefly) present one such computational technique, where the numerical grid follows the MHD flow using a "moving mesh".  I will then present some astrophysical scenarios for which I have applied this method, including planet formation and high-energy transients such as supernovae and gamma ray bursts.

  • High Energy Theory Seminar: "Some New Mechanisms for Baryogenesis"

    David Rittenhouse Laboratory, 2N36

    Jeremy Sakstein (U of Penn)

    There is more matter than antimatter in the universe, and the origin of this asymmetry is still a mystery. The asymmetry can be generated dynamically in the early universe in a process referred to as baryogenesis but the standard model is not able to produce the amount observed. This is one hint that there is physics beyond the standard model. In this talk, I will present two new baryogenesis mechanisms, one using scalar-tensor theories and the other using Lorentz violating theories.

  • Condensed Matter Seminar: "Enhanced optical and magnetic microscopy by orientation-dependent modulation of single-molecule and nitrogen-vacancy-center emission"

    David Rittenhouse Laboratory, A4

    Mikael Backlund (Harvard University)

    Selection rules impose geometrical constraints on the interactions of light and matter. In
    particular, an emitter with a well-defined orientation will emit photons of a characteristic
    polarization and wavevector distribution, even as viewed in the far field. Knowledge of these
    distributions can be leveraged to enhance a number of state-of-the-art microscopy techniques. In
    the first part of the talk I will discuss such an approach to single-molecule localization
    microscopy, relevant for single-molecule tracking and super-resolution imaging. It is known that