Colloquium Archives (before June 2017)

More recent colloquia are posted on the Physics & Astronomy Colloquia page.

David Hatch, University of Texas at Austin

Title: "Kinetic Plasma Turbulence: New Insights Into Its Fundamental Nature and Implications for Fusion Energy" (Video)

Abstract:  Turbulence is ubiquitous in both space and laboratory plasmas. These plasmas are often hot and/or diffuse, which requires the use of kinetic theory, the description of particle distribution functions in a high-dimensional phase space.  Turbulence in this phase space exhibits a rich variety of dynamics, altering standard fluid turbulence paradigms in fascinating ways. I will describe new insights into the fundamental nature of kinetic plasma turbulence (applicable to both natural and laboratory plasmas). I will also discuss breakthroughs in understanding and modeling plasma turbulence in fusion devices, addressing the question: what do plasma turbulence simulations say about the prospects for fusion energy and how can such simulations advance these prospects?

Zackaria Chacko, University of Maryland

Title: Neutral Naturalness   (Video)

Abstract: I explain the hierarchy problem of the standard model of particle physics, and discuss some of the ideas which have been put forward to resolve it. I then show that a specific class of theories, built around a framework known as neutral naturalness, can help address this problem while remaining consistent with all current experimental tests. I explain that while certain theories in this class give rise to striking signals, others are extremely difficult to test, and require a detailed study of the properties of the Higgs boson. I consider the implications of these results for the Large Hadron Collider, and for future experimental programs.

Yi-Hsin Liu, NASA-Goddard Space Flight Center

Title: "Magnetic Reconnection in Plasmas" (Video)

Abstract: Magnetic reconnection is the process whereby a change in topology of magnetic field lines allows for a rapid conversion of magnetic energy into thermal and kinetic energy of the surrounding plasma. This physical process plays a key role in many astrophysical and laboratory contexts, ranging from magnetospheric substorms, solar eruptions, sawtooth crashes in fusion devices and potentially the super-flares in Crab Nebula. The recently launched Magnetospheric Multiscale (MMS) mission provides an unprecedented view of the three-dimensional fine-scale structure of magnetic reconnection. It offers the amazing opportunity to combine key insights from numerical models with high quality in-situ measurements that promise to greatly increase our understanding of this crucial physical process.

Jack Sankey, McGill University

Title: "Toward Optically Defined Micromechanical Systems" (Video)

Abstract: Mechanical systems are ubiquitous throughout society, from oscillators in timekeeping devices to accelerometers and electronic filters in automobiles and cell phones. They also represent an indispensable set of tools for fundamental science, providing a means of sensing atomic-scale forces and masses or even the minuscule spacetime distortions from passing gravitational waves. In the field of optomechanics, we exploit the forces exerted by radiation to gain a new level of control over these systems at all size scales.

Andrew Fitzpatrick, Boston University

Title: "Effective Field Theory and the Phenomenology of Dark Matter Direct Detection” (Video)

Abstract: Direct detection searches for dark matter have made significant advances in their level of sensitivity and are expected to improve further in the near future.  The results of these experiments are often interpreted in a limited context of certain kinds of interactions between dark matter and standard matter, but the full range of possible interactions is much richer.  We discuss the theoretical and experimental motivation for considering a broad range of possible structure in the dark matter content of the universe, and a framework for systematically describing this wider range of possibilities.  We describe results from on-going work bringing together this framework with nuclear physics results in order to provide a complete `dictionary’ for the experimental predictions in this larger parameter space.

Mark Trodden, University of Pennsylvania

Title: "Pushing Einstein's Boundaries: Gravitational Approaches to the Challenges of Modern Cosmology" (Video)

Abstract: Einstein’s general theory of relativity (GR) is one of the most successful and well-tested physical theories ever developed. Nevertheless, modern cosmology poses a range of questions, from the smallest scales to the largest, that remain currently unresolved by GR coupled to the known energy and matter contents of the universe. This raises the logical possibility that GR may require modification on the relevant scales.

I will discuss the status of some modern approaches to alter GR to address cosmological problems. We shall see that these efforts are extremely theoretically constrained, leaving very few currently viable approaches. Meanwhile, observationally, upcoming missions promise to constrain allowed departures from GR in exciting new ways, complementary to traditional tests within the solar system. I will finish by describing some promising very recent ideas.