## Events - Weekly

Sunday,
September 25 |
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Monday,
September 26 |

Biophysics Seminar speaker Jane Wang, Cornell "Insect flight: from Newton’s law to Neurons" Joseph Henry Room · 12:00 p.m.– 1:00 p.m.HET Seminar | Vijay Balasubramanian | University of Pennsylvania | “New Forms of Entanglement and Holography” Jadwin 111 · 2:30 p.m.– 3:30 p.m. |

Tuesday,
September 27 |

Pheno & Vino Seminar, Rouven Essig, Stony Brook, "New Direct-Detection Probes of sub-GeV Dark Matter" Dark matter with MeV-to-GeV masses is a theoretically and phenomenologically interesting possibility. In this talk, I will describe how direct-detection experiments can probe this largely unexplored mass range. A particularly promising possibility is that dark matter scatters off electrons, causing ionization or excitation of atoms in a detector target material, which can lead to events containing one or more electrons or photons. I will review how existing XENON10 data probes dark matter with masses as low as a few MeV, and present an improved constraint using recent XENON100 data. After reviewing the challenges for xenon-based experiments to make further progress, I will discuss how experiments with different materials could significantly improve the sensitivity. This includes upcoming experiments using semiconductors (e.g. SuperCDMS, DAMIC) as well as new dedicated experiments using scintillators and other materials. I will focus on ideas that could be realized within the next five years, but also mention other efforts. I will also present a few simple sub-GeV dark matter models, which provide concrete experimental targets, and contrast direct-detection probes with searches at colliders and fixed-target experiments. Jadwin 303 · 4:00 p.m.– 5:30 p.m.Math Physics Seminar, Eliran Subag, Weizmann, "Critical points and the Gibbs measure of a spherical spin glass model" For integers N let H_N(x) be an isotropic Gaussian field on the N-dimensional unit sphere, meaning that Cov(H_N(x),H_N(y)) is a function, f_N, of the inner product of <x,y>. The spherical spin glass models of statistical mechanics are such random fields, with f_N = N f with the function independent of the dimension N. The intricate landscape of the graph of H_N(x) may be studies through its critical points and the corresponding values. Focusing on the pure p-spin models, I will review recent developments concerning the distribution of the number of critical values at a given height and the associated extremal point process. Combining these results with a local investigation of the behaviour of H_N(x) in neighborhoods around the critical points, we obtain a detailed geometric picture for the Gibbs measure at low enough temperature. The measure concentrates on spherical "bands" around the deepest critical points. The main focus of the talk will be on the structure of such states, and its consequences. The talk is based on a joint work with Ofer Zeitouni. Jadwin 343 · 4:30 p.m.– 5:30 p.m. |

Wednesday,
September 28 |

Thursday,
September 29 |

Special Condensed Matter Seminar, Adam Nahum, MIT, "Quantum entanglement growth under random unitary dynamics" A quantum many-body system, prepared initially in a state with low entanglement, will entangle distant regions dynamically. How does this happen? I will discuss entanglement entropy growth for quantum systems subject to random unitary dynamics — i.e. Hamiltonian evolution with time-dependent noise, or a random quantum circuit. I will show how entanglement growth in this ‘noisy’ situation exhibits remarkable universal structure, which in 1D is related to the Kardar—Parisi—Zhang equation. I will argue that understanding this structure leads us to heuristic pictures for entanglement growth which may be useful for more general (non-noisy) dynamics. PCTS Seminar Room · 2:00 p.m.– 3:30 p.m.Hamilton Colloquium Series: Frans Pretorius, Princeton; "The Dynamical Strong-field Regime of General Relativity" In this talk I will describe the recent detection of gravitational waves by the LIGO/Virgo collaboration. The main event heard, GW150914, is consistent with the emission of gravitational waves from the late inspiral, merger and ringdown of two heavy stellar mass black holes. Many aspects of this event are fortuitous and remarkable, and I will discuss what it has taught us about strong-field gravity, binary black hole populations in the universe, and what it implies we can further learn over the next few years once LIGO is upgraded to design sensitivity. Jadwin A10 · 4:30 p.m.– 6:00 p.m. |

Friday,
September 30 |

Gravity Group Seminar, Mark Kamionkowski (JHU), "Dust polarization and interstellar turbulence" Perhaps the most surprising result from the Planck satellite is the observation that the E-mode power in the dust polarization is twice that in the B mode, in stark contrast to pre-Planck expectations of roughly equal dust powers in E and B modes. I will show how the E- and B-mode powers are determined by fluctuations in the magnetized interstellar medium, the slow, fast, and Alfv\'en magnetohydrodynamic (MHD) waves. I will argue that the observed E/B ratio, as well as the TE (temperature-polarization) cross-correlation (which is observed to be positive) are not easily reconciled with expectations for the spectrum of fluctuations expected in the models of MHD turbulence usually invoked to account for the fluctuations. I will then discuss some alternative explanations (including the possibility that the scales probed by Planck overlap the outer scale for interstellar turbulence) for the dust-emission patterns seen in the Planck temperature-polarization maps. I will then outline some interesting directions for future related research. Joseph Henry Room · 12:00 p.m.– 1:30 p.m. |

Saturday,
October 1 |