## Events - Weekly

Sunday,
April 13 |
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Monday,
April 14 |

Biophysics Seminar Series - Massimo Vergassola (UCSD) “Finding the needle in a biological haystack” Early T-cell activation is selected by evolution to discriminate a few foreign peptides rapidly from a vast excess of self-peptides, and it is unclear in quantitative terms how this is possible. It will be discussed how a generic proofreading cascade supplemented by a single negative feedback accounts quantitatively for early T-cell activation, including antagonistic effects. Modulation of the negative feedback mediated by the SHP-1 phosphatase explains previous counterintuitive observations and new experiments validate predictions. Absolute limits on the tradeoffs between decision speed and accuracy are then explored. In addition to the immune system, rapidly developing embryos, and cellular response to stress, provide examples where fast and accurate actions are required. Statistical theory under the rubric of 'exploit-explore' supplies rigorous performance bounds and algorithms that realize them. It will be shown that common protein phosphorylation networks can implement optimal decision theory algorithms, and speculated that the ubiquitous chemical modifications to receptors during signaling actually perform such analogue computations. Joseph Henry Room · 12:00 p.m.– 1:00 p.m.Condensed Matter Seminar, Gil Refael, "Light matters - from Floquet topological insulators to topological polaritons" In my talk I will present fresh findings on the possibility of producing a topological polariton (nicknamed topolariton) in trivial quantum-wells coupled to extended optical cavities. The idea of a topolariton emerges naturally from the concept of Floquet topological insulators. First, I will review how an external periodic drive can lead to a Floquet topological spectrum in a trivial 2d quantum well. Next, I will focus on exciton-polaritons, and present some toy models of quantum-wells coupled to optical cavities that exhibit 'topolaritons' - i.e., chiral edge modes that are superpositions of photons and excitons. PCTS Seminar Room · 1:15 p.m.– 2:30 p.m.High Energy Theory Seminar-"BTZ/CFT" -Raman Sundrum- Uni. of Maryland Bloomberg Lecture Hall - Institute for Advanced Study · 2:30 p.m.– 3:30 p.m. |

Tuesday,
April 15 |

Wednesday,
April 16 |

Particle Physics Seminar, Francesco D'Eramo, "Anomaly Mediation from Unbroken Supergravity" In this talk I will show how the sparticle soft masses generated by anomaly mediation, proportional to the gravitino mass, should be associated to unbroken supersymmetry (SUSY). This counterintuitive result arises because the underlying symmetry structure of (broken) supergravity in flat space is in fact (unbroken) SUSY in anti-de Sitter space. When quantum corrections are regulated in a way that preserves SUGRA, the underlying AdS curvature (proportional to the gravitino mass) necessarily appears in the regulated action, yielding soft masses without corresponding goldstino couplings. I will present an explicit calculation for a simple toy model, and then I will state the general result. PCTS Seminar Room · 3:00 p.m.– 5:00 p.m. |

Thursday,
April 17 |

Special Cosmology Seminar, Clem Pryke "Detection of B-mode Polarization at Degree Angular Scales" The BICEP2 collaboration recently reported detection of an excess of B-mode power in the polarization pattern of the CMB at few degree angular scales. I will review the experiment and analysis with particular reference to measurement and control of systematics. I will also review the several lines of evidence that the signal is cosmological rather than foreground. PCTS Seminar Room · 1:30 p.m.– 3:00 p.m.Hamilton Colloquium Series - Yayu Wang, Tsinghua University, "Quantum Anomalous Hall Effect in Topological Insulators" The anomalous Hall effect was discovered more than 130 years ago in a ferromagnet, where a Hall resistance exists even in the absence of an external magnetic field. The quantized version of the anomalous Hall effect has attracted much interest since the discovery of quantum Hall effect in the 1980s. A few years ago, it was proposed that the quantum anomalous Hall effect may occur in magnetic topological insulators, but the experimental realization has been elusive. In this talk we report transport studies of magnetically doped topological insulator thin films grown by molecular beam epitaxy. We have achieved systematic tuning of the electronic band structure, magnetic ordering, and bulk band topology, which eventually led to the experimental realization of the quantum anomalous Hall effect, i.e., the quantum Hall effect in zero magnetic field. Reference: “Experimental observation of the quantum anomalous Hall effect in a magnetic topological insulator”, Science 340, 167 (2013). Jadwin A10 · 4:30 p.m.– 6:00 p.m. |

Friday,
April 18 |

Gravity Group Astrophysics|Cosmology Lunch: Sarah Shandera, "Cosmic Variance, Statistical Naturalness and Non-Gaussianity" The possibility of measuring or constraining correlations of the primordial curvature fluctuations beyond the power spectrum has opened up promising new avenues to differentiate models of inflation. Interestingly, mode coupling also introduces a new and significant uncertainty in matching observations to theory. In a universe much larger than our current Hubble volume, our local background need not agree with the global average background often used to theoretically predict the homogeneous and isotropic perturbations. If modes are coupled, the statistics of perturbations we observe (including the amplitude of non-Gaussianity) can depend on the long wavelength background which is not independently observable to us. I will discuss the implications of this result for interpreting the Planck satellite (and BICEP2) results and on the potential of future data to constrain the particle physics of inflation. Joseph Henry Room · 12:00 p.m.– 1:30 p.m.HET Seminar- Dan Harlow-PCTS-"Inflation after False Vacuum Decay: New Evidence from BICEP2". PCTS Seminar Room · 1:30 p.m.– 2:30 p.m. |

Saturday,
April 19 |