Colloquium Archives

Devin Walker, Stanford University

Title: The Quest to Understand the Nature of Dark Matter  (Video)

Abstract: I review the current status of and discuss the future prospects for accelerator, direct and indirect searches for dark matter.  I describe how each search impacts our understanding of various candidate theories as we look to the future.  Finally, I briefly emphasize how new (theoretical) “self-consistency” conditions on thermal dark matter can help to exclude candidate theories as we look toward the future.

 

David Griffiths, Reed College

Title: Hidden Momentum  (Video)

Abstract:  Electromagnetic fields carry energy, momentum, and even angular momentum. The momentum density is 0(E×B), and it accounts (among other things) for the pressure of light. But even static fields can harbor momentum, and this would appear to contradict a general theorem: if the center of energy of a closed system is at rest, then its total momentum must be zero. Evidently in such cases there lurks some other momentum, not electromagnetic in nature, which cancels the field momentum. But finding this “hidden momentum” can be surprisingly subtle. I’ll discuss a particularly nice example.

 

Christine Jones Forman, Harvard University

Title:  The Most Massive Clusters of Galaxies in the Universe

Abstract: ESA's Planck Mission has provided a large, statistically representative sample of massive clusters, detected over the full sky through their SZ effect.  Since the strength of the SZ signal is directly correlated with total cluster mass, the Planck detections provide a good estimate of the cluster mass. To better understand the growth of massive clusters, we are using Chandra observations of 165 Planck detected clusters at redshifts z<0.35 to determine cluster morphologies.  I will show a comparison of the cluster morphologies in SZ selected samples compared to X-ray and optically    selected samples.  In addition, among these very massive systems are the HST Frontier Field clusters.  For these we are combining deep X-ray, radio and optical/IR observations to better understand cluster mergers, the transformations of cluster galaxies, the generation of radio halos and relics, as well as to identify X-ray and radio AGN that are lensed by the cluster.

Robert Caldwell, Dartmouth College

Title: Echoes of the Big Bang  (Video)

Abstract: A prediction of an inflationary epoch in the early universe -- responsible for the *bang* in the Big Bang -- is a spectrum of primordial gravitational waves. In this talk, we review the mechanism that creates these waves, deconstruct the tell-tale imprint that these relics leave on the cosmic microwave background, and summarize the observational status. We also report on recent work suggesting these gravitational waves may have a preferred handedness.

Maura E. Hagan, NCAR, Boulder, CO

Title: Dynamical Connections between Meteorological and Space Weather  (Video)

Abstract: Recent investigations reveal an important and previously inconspicuous set of drivers of quiescent variability in the region of near geospace known as the thermosphere-ionosphere. These results confirm that the Earth’s atmosphere is a complex and coupled system, rather than a series of independent layers.

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