Past Events

High Energy Theory Seminar: "Discrete Superconformal Matter"
March 19, 2018  2:00 pm
David Rittenhouse Laboratory, 2N36
Paul Oehlmann (Virginia Tech)
We construct a novel type of (2,0) discrete charged superconformal matter coupled to 6d supergravity using Ftheory. For this, we consider smooth genusone fibered and compact CalabiYau threefolds quotiented by a freely acting automorphism. The resulting geometries exhibit orbifold singularities in the base with socalled multiple fibers over them which is where the (2,0) discrete charged matter resides. We show this presence to be necessary for anomaly cancellation which we proof in generality.

Astro Seminar: "Insights Into Dark Matter From the Stellar Halos of Galaxies"
March 16, 2018  1:00 pm  2:00 pm
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"
March 14, 2018  4:00 pm
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, oneway 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 madetoorder structure at length scales as short as a micron.

Astro Seminar: "The Chaotic Life Cycles of Planetary Systems"
March 14, 2018  2:00 pm
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"
March 13, 2018  1:30 pm
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 realworld 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: "CoarseGraining Holographic Entanglement"
March 12, 2018  2:00 pm
David Rittenhouse Laboratory, 2N36
Netta Engelhardt (Princeton)

Astro Seminar: "Cosmic Microwave Backlight: Illuminating LargeScale Structure with the Universe's Oldest Photons"
March 2, 2018  1:00 pm
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"
February 28, 2018  4:00 pm  5:00 pm
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"
February 28, 2018  2:00 pm
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 highenergy transients such as supernovae and gamma ray bursts.

High Energy Theory Seminar: "Some New Mechanisms for Baryogenesis"
February 26, 2018  2:00 pm
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 scalartensor theories and the other using Lorentz violating theories.