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Events During the Week of May 9th through May 16th, 2010

Monday, May 10th, 2010

No events scheduled

Tuesday, May 11th, 2010

Special Astronomy Colloquium
Extragalactic Globular Cluster Systems: Relics from the Early Epochs of Galaxy Formation
Time: 3:30 pm - 5:00 pm
Place: 3425 Sterling Hall
Speaker: Dr. Eric Peng, Kavli Institute for Astronomy and Astrophysics & Peking University
Abstract: Globular clusters are our most easily accessible local window onto the high redshift Universe. Visible out to distances of hundreds of Mpc, they are the "tip of the iceberg" for the oldest stars -- populations which are otherwise extremely difficult to study in distant galaxies.
HST and ground-based surveys of nearby galaxy clusters are transforming our view of these halo populations. I will discuss the ways in which extragalactic globular systems are teaching us about galaxy assembly, and will present recent results from the ACS Virgo and Fornax Cluster Surveys, the HST/ACS Coma Cluster Treasury Survey, and the Next Generation Virgo Survey.
Host: Christy Tremonti
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Wednesday, May 12th, 2010

String Theory Seminar
(Note special date & time)
Stability of non-BPS states in heterotic string theory
Time: 4:00 pm
Place: 5280 Chamberlin Hall
Speaker: Jihye Seo, Harvard University
Abstract: We study BPS and non-BPS states in heterotic string theory compactified on 4-torus. A non-BPS state can decay into a set of BPS states with same total charge and smaller total mass. We organize conservation of the charges using a set of eight 16 by 16 transformation matrices acting on a 16 dimensional lattice, in order to constrain possible decay modes allowed by charge conservation. We find that a non-BPS state with spinor representation is rather robust against decays into BPS states. We identify its huge stability region in moduli space of a 4-torus, and we prove that no other decays into BPS states are possible. Without fine tuning, we achieve an exact stablity for a non-BPS state, and this may turn useful for string-inspired model building. This study on non-BPS objects and their stability may also provide non-trivial tests of weak-strong duality between heterotic string theory compactified on 4-torus and Type IIA string theory on K3 surface.
Host: Shiu
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Thursday, May 13th, 2010

R. G. Herb Condensed Matter Seminar
Spin-triplet superconductivity in Co-based Josephson junctions
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Norman Birge, Michigan State University

Superconducting/Ferromagnetic (S/F) hybrid systems exhibit a number of interesting properties due to the interplay between the competing symmetries of their order parameters. With conventional spin-singlet superconductors, the proximity effect in S/F systems decays over an extremely short length scale in the ferromagnet due to the large exchange splitting between the spin-up and spin-down electron bands. In S/F/S Josephson junctions, the critical current oscillates and decays rapidly as a function of the ferromagnetic layer thickness. If there were spin-triplet superconducting correlations present, however, then both the proximity and Josephson effects would persist over much longer distances. Such correlations have been predicted to occur in S/F systems with certain forms of magnetic inhomogeneity near the S/F interface. Moreover, these correlations exhibit a strange symmetry never before observed: they are odd in frequency or time. In this talk I will discuss our efforts to produce and measure these elusive spin-triplet correlations in S/F/S Josephson junctions, culminating in our very recent success.1

1 T.S. Khaire, M.A. Khasawneh, W.P. Pratt, Jr., and N.O. Birge, Phys. Rev. Lett. 104, 137002 (2010).

Host: Robert McDermott
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Atomic Seminar
Polarization and hyperfine transitions of metastable <sup>129</sup><i>Xe</i> in discharge cell, & Nonlinear Pressure Shifts of Cs Atoms in Neon
Time: 2:00 pm
Place: 5280 Chamberlin
Speaker: Tian Xia, Princeton University

Part I: Polarization and hyperfine transitions of metastable 129Xe in discharge cell

The polarization and relaxation rates of metastable 129Xe atoms are measured with magnetic resonance spectroscopy, at both microwave frequencies, where ΔF = 1 transitions are induced between the sublevels, and at radiofrequencies, corresponding to ΔF = 0 transitions. Unlike earlier work, which mostly used ΔF = 0 radiofrequency (rf) resonances for monitoring spin polarization of even isotopes of the metastable atoms, the work reported here was focused on the isotope 129Xe , where we used both ΔF = 0 rf resonances and Δ F = 1 microwave resonances. This permits us to more unambiguously determine the degree of nuclear spin polarization of the optically pumped metastable atoms. The nuclear spin polarization of the resonant velocity group is measured to be 22 +/- 2%. The relaxation of metastable xenon atoms is dominated by depolarizing collisions with ground state atoms, with lesser contributions from metastability exchange collisions.

Part II: Nonlinear Pressure Shifts of Cs Atoms in Neon

I demonstrate that the hyperfine resonance frequency of ground state Cs atoms have a nonlinear dependence on the pressure of the buffer gas Ne at a fixed temperature. The hyperfine resonance frequency of alkali-metal atoms is shifted by an amount, which had long been assumed to be linear with the buffer gas pressure until Fei Gong discovered that the shift of Rb and Cs hyperfine resonance frequency has a nonlinear dependence on the pressure of the buffer gas Ar and Kr. I found that the nonlinear pressure shift of Cs hyperfine frequency in Ne is positive. The reason of the nonlinear shift is the three body collision (eg: Cs-Ne-Ne) and the formation of Van der Waals molecules of a Cs atom and a buffer gas atom of Ar, Kr, or Ne. The hyperfine precession rate of a Cs atom bound in molecule has a shift respect to a free Cs atom.

Host: Mark Saffman & Thad Walker
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Joint Seminar with String Theory
Inflationary Cosmology on Trial
Time: 4:00 pm
Place: 4274
Speaker: Paul Steinhardt, Princeton University
Host: Gary Shiu
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Friday, May 14th, 2010

Theory/Phenomenology Seminar
Title to be announced
Time: 2:30 pm - 3:30 pm
Place: 5280 Chamberlin Hall
Speaker: Jong-Chul Park, Korea Institute for Advanced Study
Host: Ian-Woo Kim
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