## Events - Weekly

**May 2013 >>**

Sunday,
May 12 |
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Monday,
May 13 |

Condensed Matter Seminar, Liang Fu, MIT, From Topological Crystalline Insulator to Anderson Transition Structure and symmetry play important roles in determining electronic properties of periodic solids. The interplay between crystalline symmetry and electronic topology leads to new phases of matter dubbed topological crystalline insulators, which possess protected surface states with unique and tunable electronic properties. In this talk, I will describe theoretical prediction of topological crystalline insulators in the SnTe class of IV-VI semiconductors, and experimental observation of topological surface states. The robustness of such surface states against strong disorder has motivated a re-examination of theory of Anderson localization. I will describe a new field theory for Anderson transition in the two-dimensional symplectic class, in which topological defects drive localization and the sign of defect fugacity determines the topological class of the localized phase. This leads to a unifying picture that all metal-insulator transitions in two dimensions are topological phase transitions. References: [1] L. Fu, Phys. Rev. Lett. 106, 106802 (2011). [2] T. H. Hsieh, H. Lin, J. Liu, W. Duan, A. Bansil, and L. Fu, Nat. Commun., 3, 982 (2012). [3] L. Fu and C. L. Kane, Phys. Rev. Lett. 109, 246605 (2012). PCTS Seminar Room · 1:15 p.m.– 2:30 p.m.High Energy Theory Seminar - IAS - Alexander B. Zamolodchikov, Rutgers, The State University NJ - Classical Conformal Block and Painleve VI Classical conformal blocks appear in the limit c->infinity ofthe Virasoro conformal blocks. Classical conformal blocks have close relationship to monodromy of the second order differential equations with regular singularities. I will discuss relation of 4-point classicalconformal blocks to special solutions of Painleve VI equation. Bloomberg Lecture Hall - Institute for Advanced Study · 2:30 p.m.– 4:00 p.m. |

Tuesday,
May 14 |

High Energy Theory Seminar - IAS - Josef Pradler, Johns Hopkins University - Dark Photons in Cosmology, Astrophysics and Experiment Light new particles with masses well below the GeV-scale are an often considered and plausible extension of the Standard Model. In this talk I will present new results on dark photons, a massive vector boson kinetically mixed with the photon. The model serves as a prototype scenario for energy injection in the early Universe and we will use it to survey more recent developments in Big Bang Nucleosynthesis which includes a new solution to the cosmological lithium problem. If dark photons have masses below 10 keV they will also be emitted from the interior of stars. In a second part of the talk, we identify a new stellar energy loss mechanism originating from a resonant production of dark photons. Compared to previous analyses, limits on dark photons are significantly improved, to the extent that many dedicated experimental searches now find themselves deep inside astrophysically excluded regions. In a final part of the talk, we demonstrate that constraints on the atomic ionization rate imposed by the results of the XENON10 experiment make low-threshold Dark Matter experiments the most sensitive dark vector helioscopes, surpassing even the most stringent astrophysical and cosmological limits. Bloomberg Lecture Hall - Institute for Advanced Study · 1:30 p.m.– 2:30 p.m. |

Wednesday,
May 15 |

Thursday,
May 16 |

Friday,
May 17 |

High Energy Theory Seminar - Radu Roiban, Penn State - On the one-loop S matrix of certain reduced supersymmetry supergravity theories We construct all supergravity theories that can be obtained through factorized projections of N = 8 supergravity, exposing their double-copy structure, and calculate their one-loop four-point scattering amplitudes. We derive representations of gluon amplitudes in N=1 and N=2 theories obeying color/kinematics duality and discuss their properties vis a vis those of N=4 super-Yang-Mills amplitudes and highlight the contribution to supergravity amplitudes of terms that integrate to zero. We also discuss a large (but not exhaustive) set of projections leading to theories with no obvious double-copy structure and observe a unified structure in both matter and gravity amplitudes. For N=4 supergravity with and without further matter vector multiplets we discuss the anomaly of a U(1) subgroup of the duality group, construct the anomalous part of the one-loop effective action and identify the reflection of the anomaly in the supergravity S-matrix. A similar anomalous symmetry exists for N<4 supergravities as well. PCTS Seminar Room · 1:30 p.m.– 2:30 p.m. |

Saturday,
May 18 |