Applied Physics / Physics Colloquium

Applied Physics/Physics Colloquium: Top Quarks: The New Flavor

Topic: 
Top Quarks: The New Flavor
Abstract / Description: 

The Large Hadron Collider is providing an enormous dataset of proton-proton collisions at the highest energies ever achieved in a laboratory.

With our new ability to study the Higgs boson and the unprecedentedly large sample of top quarks, a new frontier has opened: the flavor physics of the top quark - at heart, the question of how the top quark interacts with the Higgs field. We can start to ask questions such as whether the Higgs field is the unique source of the top quark's mass and whether there are unexpected interactions between the top quark and the Higgs boson. The answers to these questions will shed light on what may lie beyond the particle physics Standard Model and have cosmological implications.

Date and Time: 
Tuesday, April 10, 2018 - 4:30pm
Venue: 
Hewlett 201

Applied Physics/Physics Colloquium: The Search for Dark Energy and NASA’s WFIRST mission

Topic: 
The Search for Dark Energy and NASA’s WFIRST mission
Abstract / Description: 

Over the last twenty years, there has been growing evidence that our universe is dominated by dark energy. The nature of this dark energy remains a mystery. Is it the signature of the breakdown of general relativity or vacuum energy associated with quantum gravity? I will review the current observations and note the intriguing tensions between measurements based on the cosmic microwave background (CMB) and local measurements of the expansion rate of the universe and the amplitude of density fluctuations. I will then discuss on-going and upcoming CMB experiments and the role of the WFIRST mission in studying the nature of dark energy. I will also discuss the broader scientific mission of the WFIRST mission and its current status.

Date and Time: 
Tuesday, March 13, 2018 - 4:30pm
Venue: 
Hewlett 201

Applied Physics/Physics Colloquium: The Entropic Matter(s) of an Ordered Universe

Topic: 
The Entropic Matter(s) of an Ordered Universe
Abstract / Description: 

Cosmic Information Theory and Analysis, CITA@CITA, uses entropy constrained by control/order parameters to relate our increasingly highly-entangled Cosmic Microwave Background and Large Scale Clustering big-sky data to how our Universe morphed from a coherently smooth accelerating Hubble-patch into the intricate evolving complexity of the cosmic web. I will chat about ongoing problems in (non-equilibrium) Information-Entropy generation: in post-inflation shock-in-time heating, stored now mostly in the cosmic photon and neutrino seas; in the space-shocked web of galaxies and clusters and its accompanying nuclear/black hole cosmic infrared waste. Central to our statistical analyses are the all-sky deep-volume ensembles of "webskys" we build to mock the real-sky webskys we observe. As in particle physics, simulating and discovering what lies Beyond the Standard Model of Cosmology is the goal, as yet with no B in the SMc in spite of tantalizing 2sigma-ish SMc anomalies and tensions.

Date and Time: 
Wednesday, March 7, 2018 - 4:30pm
Venue: 
Hewlett 201

The 2018 Robert Hofstadter Memorial Lecture: The Dawn of Gravitational-Wave Astrophysics

Topic: 
The Dawn of Gravitational-Wave Astrophysics
Abstract / Description: 

In the past two years the gravitational-wave detections enabled by the LIGO detectors have launched a new field in observational astronomy allowing us to study compact object mergers involving pairs of black holes and neutron stars. I will discuss what current results reveal about compact object astrophysics, from binary black hole formation to short gamma-ray bursts and nuclear matter physics. I will also highlight what we can expect in the near future as detectors' sensitivity improves and multi-messenger astronomy further advances.

Date and Time: 
Tuesday, April 3, 2018 - 4:30pm
Venue: 
Hewlett 201

The 2018 Robert Hofstadter Memorial Lecture: Cosmic Collisions Reveal Einstein's Gravitational-Wave Universe

Topic: 
Cosmic Collisions Reveal Einstein's Gravitational-Wave Universe
Abstract / Description: 

For the first time, scientists have observed ripples in the fabric of spacetime called gravitational waves, arriving at the earth from a cataclysmic event in the distant universe. This confirms a major prediction of Albert Einstein's 1915 general theory of relativity and opens an unprecedented new window onto the cosmos. Gravitational waves carry unique information about their dramatic origins and about the nature of gravity that cannot otherwise be obtained. Detected gravitational waves were produced during the final fraction of a second of the mergers of two black holes but also during the last hundred seconds of the collision of two neutron stars. The latter is the first ever cosmic event to be observed both in gravitational waves and in electromagnetic waves, shedding light on several long-standing puzzles, like the production of gold in nature and the physics origins of brief gamma-ray flashes. I will review the beginnings of this exciting field of cosmic exploration and the unprecedented technology and engineering that made it possible.

Date and Time: 
Monday, April 2, 2018 - 7:30pm
Venue: 
Hewlett 200

Applied Physics/Physics Colloquium: Topological Quantum Chemistry

Topic: 
Topological Quantum Chemistry
Abstract / Description: 

The past decade has seen tremendous success in predicting and experimentally discovering distinct classes of topological insulators (TIs) and semimetals. We review the field and we propose an electronic band theory that highlights the link between topology and local chemical bonding, and combines this with the conventional band theory of electrons. Topological Quantum Chemistry is a description of the universal global properties of all possible band structures and materials, comprised of a graph theoretical description of momentum space and a dual group theoretical description in real space. We classify the possible band structures for all 230 crystal symmetry groups that arise from local atomic orbitals, and show which are topologically nontrivial. We show how our topological band theory sheds new light on known TIs, and demonstrate the power of our method to predict a plethora of new TIs.

Date and Time: 
Tuesday, February 27, 2018 - 4:15pm
Venue: 
Hewlett 201

Applied Physics/Physics Colloquium: Magic Angle Graphene: A New Platform for Strongly Correlated Physics

Topic: 
Magic Angle Graphene: A New Platform for Strongly Correlated Physics
Abstract / Description: 

The understanding of strongly-correlated quantum matter has challenged physicists for decades. Such difficulties have stimulated new research paradigms, such as ultra-cold atom lattices for simulating quantum materials. In this talk I will present a new platform to investigate strongly correlated physics, based on graphene moiré superlattices. In particular, I will show that when two graphene sheets are twisted by an angle close to the theoretically predicted 'magic angle', the resulting flat band structure near the Dirac point gives rise to a strongly-correlated electronic system. These flat bands exhibit half-filling insulating phases at zero magnetic field, which we show to be a Mott-like insulator arising from electrons localized in the moiré superlattice. These unique properties of magic-angle twisted bilayer graphene open up a new playground for exotic many-body quantum phases in a 2D platform made of pure carbon and without magnetic field. The easy accessibility of the flat bands, the electrical tunability, and the bandwidth tunability though twist angle may pave the way towards more exotic correlated systems, such as quantum spin liquids. I will end my talk with an unconventional experimental surprise.

Date and Time: 
Tuesday, February 13, 2018 - 4:30pm
Venue: 
Hewlett 201

Applied Physics/Physics Colloquium: Sloppy models, Differential geometry, and How Science Works

Topic: 
Sloppy models, Differential geometry, and How Science Works
Abstract / Description: 

Models of systems biology, climate change, ecosystems, and macroeconomics have parameters that are hard or impossible to measure directly. If we fit these unknown parameters, fiddling with them until they agree with past experiments, how much can we trust their predictions? We have found that predictions can be made despite huge uncertainties in the parameters – many parameter combinations are mostly unimportant to the collective behavior. We will use ideas and methods from differential geometry to explain what sloppiness is and why it happens so often. We show that physics theories are also sloppy – that sloppiness may be the underlying reason why the world is comprehensible.

Date and Time: 
Tuesday, February 20, 2018 - 4:30pm
Venue: 
Hewlett 201

Applied Physics/Physics Colloquium: Extrasolar Planets

Topic: 
Extrasolar Planets
Abstract / Description: 

Over the past two decades, thousands of planets have been discovered orbiting nearby stars, and our perspective on the universe has changed. We now know planets are not rare. We also know planets are diverse - with our biased measurements, a vast range of planetary types and system architectures have been discovered, from systems containing hot Jupiter-like planets orbiting incredibly close to their star, to densely-packed systems of "super-Earth" planets in dynamically complex configurations. Most known systems are radically different than our own; to what extent this is a measurement bias remains unclear, and the question of the frequency of habitable planets is not yet settled. I will review key discoveries over the past decade, by both the Kepler mission and ground-based facilities, and provide perspective on the uncertainties. I will also focus on results from the Gemini Planet Imager, which has produced high-SNR images and spectra of giant planets orbiting far (10-100 AU) from young (10-300 million year) stars. Finally, I will review prospects from the near future (the James Webb Space Telescope) to potential Earth-characterizing missions.

Date and Time: 
Tuesday, February 6, 2018 - 4:30pm
Venue: 
Hewlett 201

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