Gravity Group Lunch Seminar
October 7, 2016
Paul Steinhardt, Anna Ijjas et al.
Early Universe Bootcamp
These two meetings will be a frank examination of current theories of the origin and evolution of the large-scale structure of the universe, especially aimed at experimentalists and observers, with ample time for questions and discussion.
The first meeting will focus primarily on big bang inflationary cosmology; the second will continue the discussion and introduce bouncing cosmology, including some recent advances.
September 30, 2016
Marc Kamionkowski, Johns Hopkins University
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.
Sep 23, 2016
Ira Thorpe, Goddard Space Flight Center
The success of LISA Pathfinder and the prospects for a space-based gravitational wave observatory.
A space-based gravitational wave observatory targeting the milliHertz frequency band has the potential to inform many areas of physics and astrophysics including the nature of gravity in the strong-field limit, the formation and growth of massive black holes and their host galaxies, and the demographics of stellar compact objects. This strong science case has led to the Laser Interferometer Space Antenna (LISA) mission concept consistently receiving high rankings in major reviews in both the US and Europe. In 2016, the ESA-led LISA Pathfinder mission validated several key technologies for LISA and further strengthened the case for a timely implementation of LISA. In this talk, I will discuss the preliminary results from LISA Pathfinder and the outlook for a LISA-like mission in light of the successes of Pathfinder and LIGO.
Huan Yang (short talk)
Global Crustal Dynamics of Magnetars in Relation to Their Transient X-ray Outbursts", based on arXiv:1608.02633
In this talk, I will briefly discuss the yielding response of a neutron star crust to smooth, unbalanced Maxwell stresses imposed at the core-crust boundary, and the coupling of the dynamic crust to the external magnetic field. We have developed a global and time-dependent model of elastic, plastic, magnetic, and thermal evolution. Such model provides an unified framework to understand various Magnetar bursts: the (~0.1s) short bursts, and giant flares and quasi-periodic oscillations (QPOs).