Dwarf Galaxies as Astrophysical LaboratoriesJosh Simon
Room Auditorium 11:15 11:00 Coffee, Tea and more The dwarf galaxies orbiting the Milky Way are the oldest, least luminous, most dark matter-dominated, and least chemically evolved stellar systems known. To begin, I will provide a brief introduction to these galaxies, highlighting the recent discovery of large numbers of ultra-faint dwarf galaxies. I will then explain how we can measure their dark matter content and describe some of the numerous ways that dwarfs are being used to constrain the properties of dark matter. Finally, I will show how chemical abundance measurements of dwarf galaxy stars provided critical insight into r-process nucleosynthesis prior to the LIGO discovery of a neutron star merger.
Radiation-Dominated Black Hole Accretion FlowsJames Stone
Room Auditorium 00:00 11:00 Coffee, Tea and more At high accretion rates, the outward force of radiation pressure generated by energy released by infalling matter can exceed the inward pull of gravity. Such super-Eddington accretion flows occur in many systems, such as the inner regions of quasars and luminous AGN, ultra-luminous X-ray sources (ULXs), and tidal disruption events. Understanding such flows is important not only for interpreting the spectra and variability of these sources, but also to predict the rate of growth of black holes in the early universe, and to quantify energy and momentum feedback into the medium surrounding the black hole, a process likely to be important in galaxy formation. New results from a study of the magnetohydrodynamics of luminous accretion flows, in which radiation pressure dominates, will be presented. Our results reveal new physical effects, such as turbulent transport of radiation energy, that require extension of standard thin-disk models. We discuss the implications of our results for the astrophysics of accreting black holes.
Designing the optimal waveStefan Rotter
Room Auditorium 11:15 11:00 Coffee, Tea and more I will speak about newly emerging approaches for designing wave fronts that are optimal for various purposes such as for focusing waves on a target, for manipulating small particles with light, or for precision measurements in general. The theoretical concept enabling the optimal solutions for all of these diverse applications turns out to be an operator introduced by Wigner and Smith based on a system’s scattering matrix. I will provide a review of this concept and shall illustrate how experimental access to the Wigner-Smith operator enables wave-front shaping protocols at the optimal level of efficiency.
Highly magnified gravitationally lensed stars as a probe to the nature of dark matterJordi Miralda-Escude
Room Auditorium 11:15 11:00 Coffee, Tea and more Dark matter continues to pose one of the most important questions in modern cosmology. Gravitationally lensed multiple images of galaxies, quasars and stars provide several opportunities for testing the clumpiness of dark matter on small scales due to, for example, compact objects, axion mini-clusters and waves, or subhalos orbiting on galactic or cluster dark matter halos. The idea of using highly magnified stars by lensing clusters to probe this small-scale granularity in the dark matter will be discussed.
Testing Gravity with Cold AtomsGuglielmo M. Tino
Room Auditorium 11:15 11:00 Coffee, Tea and more The ability to control the quantum degrees of freedom of atoms using laser light opened the way to precision measurements of fundamental physical quantities. I will describe experiments for precision tests of gravitational physics using new quantum devices based on ultracold atoms, namely, atom interferometers and optical clocks. I will report on the measurement of the gravitational constant G with a Rb Raman interferometer, on experiments based on Bloch oscillations of Sr atoms confined in an optical lattice for gravity measurements at small spatial scales, and on new tests of the Einstein equivalence principle. I will also discuss prospects to use atoms as new detectors for gravitational waves and for experiments in space.
Growing Droplets in Cells and GelsEric Dufresne
Room Auditorium 11:15 11:00 Coffee, Tea and more To function effectively, living cells compartmentalize myriad chemical reactions. In the classic view, distinct functional volumes are separated by thin oily-barriers called membranes. Recently, the spontaneous sorting of cellular components into membraneless liquid-like domains has been appreciated as an alternate route to compartmentalization. I will review the essential physical concepts thought to underly these biological phenomena, and outline some fundamental questions in soft matter physics that they inspire. Then, I will focus on the coupling of phase separation to elastic stresses in polymer networks. Using a series of experiments spanning living cells and synthetic materials, I will demonstrate that bulk mechanical stresses dramatically impact every stage in the life of a droplet, from nucleation and growth to ripening and dissolution. These physical phenomena suggest new mechanisms that cells could exploit to regulate phase separation, and open new routes to the assembly of functional materials
The three jewels in the crown of the LHCYossi Nir
Room Auditorium 11:15 11:00 - Coffee, Tea and more The ATLAS and CMS experiments have made three major discoveries: The discovery of an elementary spin-zero particle, the discovery of the mechanism that makes the weak interactions short-range, and the discovery of the mechanism that gives the third generation fermions their masses. I explain how this progress in our understanding of the basic laws of Nature was achieved.
Gravity, entanglement, and bit threadsMatthew Headrick
Room Auditorium 11:15 11:00 - Coffee, Tea and more In trying to understand quantum gravity at a fundamental level, one of the most confusing questions is where the degrees of freedom are. So-called holographic dualities help with this question, by showing that certain quantum gravity theories are equivalent to conventional quantum field theories, in which we understand in principle where the degrees of freedom are and how they interact. Using such dualities, a new way of understanding entanglement in quantum gravity, involving so-called “bit threads”, has recently been developed. From this point of view, space becomes a channel for carrying entanglement of fundamental degrees of freedom. We will explain what holographic dualities are, what bit threads are, and what they might tell us about the nature of space in quantum gravity.
Pulling Yourself by your Bootstraps in Quantum Field TheoryLeonardo Rastelli
Room Auditorium 11:15 11:00 - Coffee, Tea and more Quantum field theory (QFT) is the universal language of theoretical physics, underlying the Standard Model of elementary particles, the physics of the early Universe and a host of condensed matter phenomena such as phase transitions and superconductivity. A great achievement of 20th-century physics was the understanding of weakly coupled quantum field theories where interactions can be treated as small perturbations of otherwise freely moving particles. Critical challenges for the 21st century include solving the problem of strong coupling and mapping the whole space of consistent QFTs. In this lecture, I will overview the bootstrap approach, the idea that theory space can be determined from the general principles of symmetry and quantum mechanics. This strategy provides a new unifying language for QFT and has allowed researchers to make predictions for physical observables even in strongly coupled theories. By holographic duality, the bootstrap program has also implications for the space of consistent quantum gravity theories.
The Large Synoptic Survey Telescope: Status Update and Prospects for ScienceSteven M. Kahn
Room Auditorium 11:15 11:00 - Coffee, Tae and more The Large Synoptic Survey Telescope (LSST) is a large-aperture, wide-field ground-based telescope designed to provide a time-domain imaging survey of the entire southern hemisphere of sky in six optical colors (ugrizy). Over ten years, LSST will obtain ~ 1,000 exposures of every part of the southern sky, enabling a wide-variety of distinct scientific investigations, ranging from studies of small moving bodies in the solar system, to constraints on the structure and evolution of the Universe as a whole. The development of LSST is a collaboration between the US National Science Foundation, which is supporting the development of the telescope and data system, and the US Department of Energy, which is supporting the development of the 3.2 gigapixel camera, the largest digital camera ever fabricated for astronomy. Approved in 2014, LSST is now well into construction, and is on track to beginning operations in 2022. I will review the design and technical status of the Project, and provide an overview of some of the exciting science highlights that we expect to come from this facility.