Past Events

Condensed Matter Seminar: "Ideas on magma motion within the lithosphere: percolation, channelization, and stressdriven segregation"
March 28, 2018  4:00 pm  5:00 pm
David Rittenhouse Laboratory, A4
Mousumi Roy (University of New Mexico)
Although we know that magma is generated by partial melting of rocks at depth, we have less of an understanding of the processes that transport magma from great depths (>100150 km) into the shallower (200 km) crustal plumbing systems of volcanic zones. I shall discuss how interstitial melt migrates via percolative flow, and ideas on how it eventually becomes focused and reorganized into networks. Field and geochemical observations suggest that these networks are characterized by thermal and chemical disequilibrium between the magma and surrounding rock. I

Astro Seminar: "Dark Matter Clustering in the Dissipationless Limit"
March 28, 2018  2:00 pm
David Rittenhouse Laboratory, A4
Michael Joyce (Sorbonne Université, Paris)
An accurate description and understanding of matter clustering in the strongly nonlinear regime, even neglecting baryonic physics, remains a problem which is relevant to cosmology and of fundamental interest. My talk will be structured around three questions about it: (1) How well do current simulations resolve this clustering? (2) Is the socalled "stable clustering" approximation a relevant one? (3) Are there really "universal" properties of nonlinear clustering?

High Energy Theory Seminar: (TBA)
March 26, 2018  2:00 pm
David Rittenhouse Laboratory, 2N36
Ted Jacobson (U of Maryland)

Condensed Matter Seminar: "Geometry and mechanics of feet and fins"
March 21, 2018  4:00 pm  5:00 pm
David Rittenhouse Laboratory, A4
Mahesh M. Bandi (Okinawa Institute of Science and Technology Graduate University)
The stiffness of propulsive appendages, such as feet and fins, is important in locomotory function. In this talk, I show that curvatureinduced stiffness is the common principle underlying the stiffness of both primate feet and rayed fish fins. We use mathematical models, physical models, and biological experiments to arrive at this conclusion. The principle is evident in a drooping dollar bill that significantly stiffens upon slightly curling it in the transverse direction.

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.

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.