Past Events

Condensed Matter Seminar: "Topological protection of photons"
January 10, 2018  4:00 pm  5:00 pm
David Rittenhouse Laboratory, A4
Mikael Rechtsman (Penn State University)
Topological insulators are solidstate materials whose transport properties are immune to defects and disorder due to underlying topological order. Perhaps the first such phenomenon was the quantum Hall effect, wherein the Hall conductivity is quantized and hence extremely robust. In this talk, I will present the experimental observation of the topological protection of the transport of photons (rather than electrons in the solid state) in complex dielectric structures. I will then present the obser

HET & HEE Joint Seminar: (TBA)
December 12, 2017  1:30 pm
Center for Particle Cosmology
Josh Ruderman (NYU)

Rittenhouse Lecture: "GW170817: Hearing and Seeing a Binary Neutron Star Merger"
December 6, 2017  4:00 pm
David Rittenhouse Laboratory, A8
Daniel Holz (Enrico Fermi Institute and Kavli Institute for Cosmology, U of Chicago) hosted by Bhuvnesh Jain
With the discovery of GW170817 in gravitational waves, and the discovery of an associated short gammaray burst, and the discovery of an associated optical afterglow, we have finally entered the era of gravitationalwave multimessenger astronomy. We will discuss LIGO/Virgo's detection of this binary coalescence, and explore some of the scientific implications, including confirmation of the kilonova model and implications for the origin of gold and platinum in the universe, tests of general relativity, and the first standard siren measurement of the Hubble constant.

Penn Cafe Event: "Unseen Objects in Our Solar System"
December 5, 2017  6:00 pm  7:00 pm
World Cafe Live 3025 Walnut Street
Masao Sako (U of Penn)
Masao Sako will discuss his research on searching for new orbits in the solar system. He will describe efforts to discover objects beyond the orbit of Neptune, some of which contain valuable information about the complicated dynamical history of the system. Dr. Sako will also discuss why astronomers think that there is a massive previouslyunseen planet out there, called Planet nine, and how it might be found.

High Energy Theory Seminar: “Cosmology of a FineTuned SUSY Higgs”
December 4, 2017  2:00 pm
David Rittenhouse Laboratory, 2N36
Matthew Reece (Harvard)
I will discuss some work in progress that explores whether a mildly finetuned Higgs boson, as in (mini)split supersymmetry, can have interesting or observable cosmological consequences. As moduli fields oscillate, the Higgs can respond and perhaps acquire very large values along a Dflat direction. Possible consequences involve a burst of gravitational wave production and an altered estimate of the number of efolds of inflation.

Condensed Matter Seminar: "Striped Ground States in the Hubbard Model"
November 29, 2017  4:00 pm  5:00 pm
David Rittenhouse Laboratory, A4
Steven White (University of California, Irvine)
Solving the 2D Hubbard model is one of the most wellknown outstanding problems in theoretical condensed matter physics. Various simulation techniques, such has DMRG and quantum Monte Carlo, have made dramatic strides in recent years, but they have still not provided clearcut answers for the nature of the ground state of the strongcoupling doped model.

Dissertation Defense: "Exploring the Universe with the Atacama Cosmology Telescope: PolarizationSensitive Measurements of the Cosmic Microwave Background"
November 27, 2017  3:00 pm
David Rittenhouse Laboratory, 3W2
Marius Lungu (UPenn)

High Energy Theory Seminar: "BMS Invariant Fluids"
November 27, 2017  2:00 pm
David Rittenhouse Laboratory, 2N36
Robert Penna (Columbia University)
The Bondivan der BurgMetznerSachs (BMS) group is the asymptotic symmetry group of asymptotically flat spacetime. It is related to flat gravity in the same way that the conformal group is related to anti de Sitter gravity. However, while the conformal group is well known throughout field theory, the BMS group is rather mysterious. We show that the BMS group is closely related to infinite dimensional symmetry groups governing fluid dynamics. We use a relationship between gravitating systems and lower dimensional fluids on their boundaries to give a new derivation of

High Energy Theory Seminar: "Entanglement at a Scale and Recovery Maps"
November 20, 2017  2:00 pm
David Rittenhouse Laboratory, 2N36
Nima Lashkari (MIT)
I discuss the amount of information in quantum field theory states reduced to a region, that cannot be recovered from its subregion density matrices. One can reconstruct the density matrix from its subregions using recovery maps. The vacuum of a conformal field theory is a quantum Markov state and the fixed point of both transformations. I define the entanglement of scaling as a measure of entanglement at a scale, and mention connections with Ctheorems proofs in 2, 3 and 4 dimensions.

Astro Seminar:"Probes of Primordial Black Hole Dark Matter"
November 15, 2017  2:00 pm
David Rittenhouse Laboratory, A4
Ely Kovetz (Johns Hopkins)
The LIGO observatory has reported several detections of gravitational waves from the coalescence of binary black holes. We consider the extraordinary possibility that the detected events involving heavier masses are mergers of primordial black holes making up the dark matter in the Universe.