Physics and Astronomy Colloquia, Academic Year 2015-2016

Colloquium committee: Leonardo Rastelli (Chair),  Alexandre Abanov, Thomas Allison, Matthew Dawber, Abhay Deshpande, Joanna Kiryluk, and Rosalba Perna.

Coffee & Tea served at 3:45 pm.

Talk begins at 4:15 pm.

Location: Harriman 137 (bottom of square C4 on the campus map)


Fall 2015 colloquia




Local Host

Sept. 1

Axel Drees

Stony Brook University 

Chair’s Colloquium

[recorded movie]

Sept. 8

no classes and no colloquium

Sept. 15

Andrew MacFadyen


Binary Black Hole Accretion

The centers of nearly all galaxies are now known to host super-massive black holes with masses of millions to billions times the mass of the Sun. As galaxies merge with each other over cosmic history these black holes fall to the center of the new merged galaxies and form binary systems of two black holes in orbit around each other. The black holes can merge with each other in the presence of gaseous accretion flows and are prime candidates for simultaneous observations of both gravitational waves and electromagnetic signals. I will present the results of 2D hydrodynamical simulations of circum-binary accretion disks using our new moving-mesh code DISCO. These simulations demonstrate that gas accretion is not impeded by binarity as had been previously predicted. Rather, gas is efficiently stripped from the inner edge of the circum-binary disk and enters the cavity along accretion streams, which feed persistent “mini-disks” surrounding each black hole. I will discuss characteristic periodicity in the measured accretion rate onto each BH, with implications for the quasar PG 1302-102 which has recently shown evidence for periodic variability. I will also discuss the dependence of the accretion flow on the binary mass ratio and characteristic modifications to the spectrum which arise from shock heated gas inside the circum-binary cavity. Finally, I will discuss simulations which include binary inspiral and merger due to gravitational wave emission in order to track the changes in accretion and electromagnetic radiation as the orbit shrinks.

[recorded movie]


Sept. 22

Gene Sprouse

Stony Brook University

APS Editor in Chief 2007-2015

Physics Publishing in the Internet Age
Journals still play an important role in communicating physics even though we have all sorts of other communication methods: Facebook, Twitter, Blogs, arXiv, and the internet, to name a few.  We will discuss the reasons why journals still exist, and why scientists choose different journals in which to publish.  Although most physicists are not aware of the cost, librarians are, and some journals are very expensive while others are relatively cheap.  Why do they have to cost anything?  Why don’t we just put it all on the arXiv and be done with it?  I plan to explain and discuss new developments such as ORCID, ResearchGate, SCOAP3, and Open Access journals, and answer general questions about publications.

[recorded movie]


Sept. 29

Premi Chandra

Rutgers University

The Hidden Order Mystery:  35 Years on the Trail of an Undetected Order Parameter      The development of collective long-range order by means of phase transitions occurs by the spontaneous breaking of fundamental symmetries. Magnetism is a consequence of broken time-reversal symmetry, whereas superfluidity results from broken gauge invariance.  The broken symmetry and the associated hidden order that develops below 17.5 kelvin in the heavy-fermion compound URu2Si2 has eluded identification for more than thirty years.  Here I'll review recent measurements, the constraints they place on theory, and the more general experimental support for the presence of a spinorial order parameter.  The broader symmetry implications of this radical proposal will also be discussed.  Work done in collaboration with Piers Coleman and Rebecca Flint.

References:  PC, P. Coleman and R. Flint Nature 493, 421 (2013), Phil. Mag. 94, 32 (2014), PRB 91, 205103 (2015)

[recorded movie]


Oct. 6

Hitoshi Murayama

UC Berkeley, Kavli IPMU

When a Symmetry Breaks

What is common among a magnet, a flounder, a rack of laundry, your heart on the left of your body, and the Higgs boson?  The concept of spontaneous symmetry breaking is ubiquitous among many natural phenomena.  I’ll describe the basic concept and its applications.  In particular, the original theorem does not quite work in many systems that include a magnet on your fridge.  I generalize the concept so that it is applicable to all known natural phenomena around us.  And its application to dark matter may be tested using Prime Focus Spectrograph on Subaru telescope.

[recorded movie]


Oct. 13

Aaron Lindeberg

Stanford University

Ultrafast studies of materials as they transform
Novel characterization techniques developed over the past decade or so have revolutionized our ability to visualize the microscopic processes that determine the functional properties of materials. The overarching challenge here is that the relevant time-scales and length-scales for these processes are typically 10-13 seconds (100 femtoseconds) and 10-10 m (1 Å) such that our view of how a material functions is often blurred out in time or in space.  In this talk I will describe recent experiments using femtosecond x-ray, electron, and optical pulses as a means of probing (and directing) the dynamics of materials as they transform in-situ. I will focus on two broad examples: (1) I will describe experiments probing electric field-driven structural changes in which all-optical biases at terahertz frequencies enable us to elucidate fundamental time-scales for switching in both ferroelectric and phase-change materials.  These results show, surprisingly, that one can drive large-scale reorientations of the polarization of a ferroelectric thin film on femtosecond time-scales. With respect to phase-change materials, I will show, contrary to established ideas in the field, that sub-picosecond duration electric field pulses can initiate threshold switching processes and amorphous-to-crystalline transitions, associated with novel possibilities for data storage devices operating at terahertz frequencies. (2) Finally, I will discuss experiments (and coupled first principles molecular dynamics simulations) probing dynamic rippling and deformations of monolayer transition metal dichalcogenide MoS2 films on femtosecond time-scales, as well as studies probing the interlayer coupling in multilayer MoSe2 and ReS2 films that gives rise to many of their unique functional properties. 

[recorded movie]


Oct. 20

Henriette Elvang

Michigan University

Exciting New Approaches to Scattering Amplitudes                                                        In particle physics experiments, such as the Large Hadron Collider at CERN, the scattering cross-section is the key physical observable. We calculate the cross-section from scattering amplitudes, which traditionally are expressed in terms of Feynman diagrams. When many particles are involved in a scattering process -- as for example in multi-gluon scattering -- the Feynman diagram approach becomes very difficult, even at leading order (tree-level). However, in recent years, it has been realized that amplitudes possess a very interesting mathematical structure that can be exploited to find more efficient calculational methods. Surprisingly, it also turns out that some amplitudes have interpretations as volumes of certain abstract geometric objects. Without assuming any prior knowledge of quantum field theory or Feynman rules, I will review the background and recent progress in this exciting field of research.

[recorded movie]


Oct. 27

Alberto Nicolis

Columbia University

String theory in the bathtub                                                                                                                I will describe the peculiar mechanical properties of certain string-like objects that can exist in fluids and superfluids: vortex lines and vortex rings. I will then show how these properties follow straightforwardly from the principles of effective field theory applied to strings living in a medium.

[recorded movie]


Nov. 3

Krishna Rajagopal


Doping and Probing the Original Liquid: Opportunities and Challenges from Heavy Ion Collisions

Heavy ion collisions at RHIC and the LHC recreate droplets of the matter that filled the

microseconds old universe.  These experiments have shown that this stuff, conventionally

called quark-gluon plasma (QGP), is the hottest, and most liquid, liquid phase of matter that we know of. And, it was the earliest complex matter to form in the history of the universe. After a look back at these discoveries I will focus on the central questions that they are

posing today and look at the challenges and opportunities ahead as we strive to answer them in the coming decade.  Questions that I will pose, but that cannot yet be answered, include:  How does QGP work? How does its liquidness emerge from its simple microscopic dynamics? Using the probes that we have at our disposal, how can we best “look under the hood”?  What is the smallest possible droplet of QGP that behaves hydrodynamically?  How does QGP form in heavy ion collisions? (One thing we know is that the answer is different than in cosmology, because heavy ion collisions are lumpy and rapid.) What is the phase diagram of doped QGP? Can we see the quantum aspects of QGP?

[recorded movie]


Nov. 10

Thomas Guhr

University of Duisburg-Essen

Random Matrices: Tour d’Horizon 

Random Matrix Theory (RMT) for dynamical systems was introduced by Wigner in the 50's and found fruitful applications for modeling spectral properties in many-body systems, particularly in nuclei. RMT is closely connected to various aspects of harmonic analysis in mathematics. In the 80's a burst of activities started, when the relevance of RMT for mesoscopic systems and quantum chaos was discovered. Moreover supersymmetry became indispensable for calculations which now also catches the attention in the mathematics community. RMT is nowadays ubiquitous in physics, statistics and mathematics, and continues to find new applications in, e.g., wireless communication and finance. I will try to give a broad overview for non-experts without going into the technical details. Given the enormous range of RMT applications, I have to restrict myself to a selection of conceptually important aspects. 

[recorded movie]


Nov. 17

Chang Kee Jung

Stony Brook University

Neutrinos, Nobel Prizes, Breakthroughs and Future 

Neutrinos are perhaps the most enigmatic particles among the matter-field particles. Because of its fundamental "lack of interactions" it took many decades for its properties to be studied in detail since its existence was conceived by Pauli in 1930's. Also because of these intrinsic difficulties historically the experimental findings on neutrinos have been often surprising, often disagreeing with theoretical expectations and sometimes even controversial. I would say that in the neutrino field overall the experiments have led the theories, not the other way around as is the case in the collider physics field. Consequently, several Nobel prizes have been awarded to the neutrino experiments. In particular, most recently, the Nobel Prize in Physics 2015 was awarded to Takaaki Kajita and Art McDonald for the discovery of neutrino oscillations. Also just last week, the Breakthrough Prize for Fundamental Physics 2016 has been awarded to the neutrino oscillation expriments. 

In this talk, I will discuss some breakthrough advances in neutrino physics through historical perspectives, especially in connection with the Nobel prizes. I will discuss what makes an experiment a Nobel prize worthy, who gets the prize and why some prizes are given so late. I will also share some personal anedotes that I have gained during my a quarter century of research in the neutrino field.

Our study on neutrinos has not been completed yet. For example, matter-antimatter asymmetry is one of the most outstanding mysteries of the universe that provides a necessary condition to our own existence. It is generally agreed that experimental observation of CPV in the lepton sector could provide us with a critical clue to this profound mystery.

Recent T2K data show an intriguing initial result on the ΔCP, which is further corroborated by the Super-Kamiokande atmospheric neutrino results as well as the most recent results from NOvA. Ultimately, however, in order to establish unequivocal results on leptonic CPV, we need a next generation experiment with a more powerful beam, and a larger and/or higher resolution detector. The Deep Underground Neutrino Experiment (DUNE) in US is such an experiment.

[recorded movie]


Nov. 24

Albert Stolow

University of Ottawa and Molecular Photonics Group

Molecules in Laser Fields: Non-adiabatic Dynamics, Quantum Control, Strong Field Physics

The most general molecular dynamic processes involve the coupled flow of both electronic charge and vibrational energy. Experimental methods such as Time-Resolved Photoelectron Spectroscopy are powerful probes of these ultrafast non-adiabatic dynamics in molecules [1]. The most information, however, obtains by observing such dynamics from the Molecular Frame of reference, avoiding loss of information due to orientational averaging. Borrowing techniques from particle physics, Time-Resolved Coincidence Imaging Spectroscopy observes the kinematically complete 3D momentum recoil vectors of emitted molecular fragments and electrons - in coincidence and as a function of time. This allows for study of the time evolution of both scalar and vector correlations during molecular processes. One important Molecular Frame vector correlation permits imaging of electronic wavefunction evolution [2] during dynamic processes. An alternative method, based on using the non-resonant Dynamic Stark Effect to align molecules in space, also permits direct time-resolved imaging of electronic dynamics in the Molecular Frame [3,4]. As laser fields get stronger still, a new laser-matter physics emerges for polyatomic systems wherein the approximations implicit in standard atomic strong field ionization models can fail dramatically. A new Nonadiabatic Multi-Electron dynamics emerges [6] and has important consequences for all strong field processes in polyatomic molecules, including high harmonic generation [7] and attosecond spectroscopy. An experimental method, Channel-Resolved Above Threshold Ionization, directly unveils the multiple electronic continua participating in the attosecond molecular strong field response [8,9].

[1] Nature 401, 52, (1999).  [2] Science 311, 219 (2006).  [3] Science 323, 1464 (2009).  [4] Phys.Rev.Lett. 97, 173001 (2006);  97, 173001 (2006).  [6] Phys.Rev.Lett. 86, 51 (2001); 93, 203402 (2004); 93, 213003 (2004).  [7]. Science 322, 1207 (2008).  [8] Science 335, 1336 (2012).  [9] Phys.Rev.Lett. 110, 023004 (2013)

[recorded movie]


Dec. 1

Julie McEnery


Exploring the Extreme Universe with Fermi

Following its launch in June 2008, high-energy gamma-ray observations by the Fermi Gamma-ray Space Telescope have unveiled thousands of new sources and opened an important and previously unexplored window on wide variety of phenomena. These have included the discovery of a population of pulsars pulsing only in gamma rays; the detection of photons up to 10s of GeV from gamma-ray bursts, enhancing our understanding of the astrophysics of these powerful explosions; the detection of hundreds of active galaxies; a measurement of the high energy cosmic-ray electron spectrum which may imply the presence of nearby astrophysical particle accelerators; the determination of the diffuse gamma-ray emission with unprecedented accuracy and the constraints on phenomena such as supersymmetric dark-matter annihilations and exotic relics from the Big Bang.  Continuous monitoring of the high-energy gamma-ray sky has uncovered numerous outbursts from active galaxies and the discovery of transient sources in our galaxy. In this talk I will describe the current status of the Fermi observatory, review the science highlights and discuss future opportunities with Fermi.

[recorded movie]






Spring 2016 colloquia




Local Host

Jan. 26

Abhay Deshpande
Stony Brook University

Reaching the next QCD Frontier: Physics of the Electron Ion Collider

In its 2015 Long Range Plan the US Nuclear Science Advisory Committee recommended that a high-energy high-luminosity polarized Electron Ion Collider (EIC) be the highest priority new facility to be constructed in the US — after the completion of the FRIB (Facility for Radioactive Isotope Beams) — which is currently being built. In this talk I will summarize the  physics case for the Electron Ion Collider and how it will address some of the most compelling and fundamental questions in QCD. I will present the status of the project and the prospects of its realization in the next decade.

[recorded movie]

Feb. 2

Jeremy Levy
University of Pittsburgh

Etch-a-Sketch Nanoelectronics


The study of strongly correlated electronic systems and the development of quantum transport in nanoelectronic devices have followed distinct, mostly non-overlapping paths.  Electronic correlations of complex materials lead to emergent properties such as superconductivity, magnetism, and Mott insulator phases.  Nanoelectronics generally starts with far simpler materials (e.g., carbon-based or semiconductors) and derives functionality from doping and spatial confinement to two or fewer spatial dimensions.  In the last decade, these two fields have begun to overlap.  The development of new growth techniques for complex oxides have enabled new families of heterostructures which can be electrostatically gated between insulating, ferromagnetic, conducting and superconducting phases.   In my own research, we use a scanning probe to “write” and “erase” conducting nanostructures at the LaAlO3/SrTiO3 interface with a precision of two nanometers.  A wide variety of nanoscale devices have already been demonstrated, including nanowires, nanoscale photodetectors, THz emitters and detectors, tunnel junctions, diodes, field-effect transistors, single-electron transistors, superconducting nanostructures and quantum point contacts. These building blocks may form the basis for novel technologies, including a platform for complex-oxide-based quantum computation and quantum simulation.

[recorded movie]


Feb. 9

David Simmons-Duffin

The Conformal Bootstrap: From Magnets to Boiling Water

Conformal Field Theory (CFT) describes the long-distance dynamics of numerous quantum and statistical many-body systems. The long-distance limit of a many-body system is often so complicated that it is hard to do precise calculations. However, powerful new techniques for understanding CFTs have emerged in the last few years, based on the idea of the Conformal Bootstrap. I will explain how the Bootstrap lets us calculate critical exponents in the 3d Ising Model to world-record precision, how it explains striking relations between magnets and boiling water, and how it can be applied to questions across theoretical physics.

[recorded movie]


Feb. 16

Philip Bucksbaum

Stanford University

Molecular movies: how to make them and what are the good for?

Strong laser fields can induce motion in molecules through sudden momentum transfer to electrons.  Tools now exist to extract both spatial and temporal information about the subsequent electronic and atomic motion on time scales as short as attoseconds. I will show how ultrashort pulse lasers, high harmonics and x-ray free electron lasers are important tools for this quantum cinematography.

[recorded movie]


Feb. 23

Samir Mathur

Ohio State

Resolution of the black hole information paradox

Some 40 years ago Hawking found a remarkable contradiction: if we accept the standard behavior of gravity in regions of low curvature, then the evolution of black holes will violate quantum mechanics. Resolving this paradox would require a basic change in our understanding of spacetime and/or quantum theory. This paradox has found an interesting resolution through string theory. While quantum gravity is normally expected to be important only at distances of order planck length, the situation changes when a large number N of particles are involved, as for instance in the situation where we make a large black hole. Then the length scale of quantum gravity effects grows with N, altering the black hole structure to a "fuzzball"; this effect resolves the paradox. 

[recorded movie]


Mar. 1

Sergei Klimenko

The LIGO collaboration and the VIRGO collaboration

Observation of Gravitational Waves by LIGO

On September 14, 2015 at 5:51 a.m. Eastern Daylight Time,  the twin Laser Interferometer Gravitational-wave Observatory (LIGO)  detectors, located in Livingston, Louisiana, and Hanford, Washington,  USA both measured ripples in the fabric of spacetime – gravitational waves  – arriving at the Earth from a cataclysmic event in the distant universe.  A century after the fundamental predictions of Einstein and  Schwarzschild, the gravitational waves are captured.

This discovery comes at the culmination of decades of instrument research and development, through a world-wide effort of thousands of researchers. I will talk about the LIGO detectors, detection details, nature of the source and the results of this observation.

[recorded movie]

Dmitri Tsybychev

Mar. 8

Nuh Gedik


Shining light on Topological Insulators

Topological insulators are novel materials that do not conduct electricity in their bulk but possess exceptional conducting electronic states on their surface. These surface electrons have a number of highly unusual characteristics: (i) they behave like massless relativistic particles similar to photons (ii) their spin is locked perpendicular to their momentum and (iii) this state is robust against moderate disorder. Understanding and characterizing unique properties of these materials can lead to novel applications such as current induced magnetization or extremely robust quantum memory bits. In this talk, I will first give a brief introduction to these materials and then describe our recent experiments in which we used ultrashort laser pulses to probe and control properties of the topological surface states. Utilizing the short duration of these pulses, we succeeded in capturing femtosecond movies of the electronic energy bands in a three dimensional manner. These movies reveal an exotic hybrid state between electrons and light, which was predicted theoretically but has never been observed in solids before.

[recorded movie]


Mar. 15

no colloquium—Spring Break

Mar. 22

Jane Wang

Cornell University

Insect Flight: From Newton's Law to Neurons

Why do animals move the way they do? Bacteria, insects, birds, and fish share with us the necessity to move so as to live. Although each organism follows its own evolutionary course, it also obeys a set of common laws. At the very least, the movement of animals, like that of planets, is governed by Newton’s law: All things fall. On Earth, most things fall in air or water, and their motions are thus subject to the laws of hydrodynamics. Through trial and error, animals have found ways to interact with fluid so they can float, drift, swim, sail, glide, soar, and fly. This elementary struggle to escape the fate of falling shapes the development of motors, sensors, and mind. Perhaps we can deduce parts of their neural computations by understanding what animals must do so as not to fall.

I will discuss recent developments along this line of inquiry in the case of insect flight. Asking how often a fly must sense its orientation in order to balance in air has shed new light on the role of motor neurons and steering muscles responsible for flight stability.

[recorded movie]


Mar. 29

David Huse

Princeton University

Many-body Anderson localization and quantum thermalization

In Anderson's 1958 localization paper, he started with the many-body problem of interacting spins doped in to a semiconductor, conjecturing many-body localization at high temperature. Then he simplified to noninteracting particles, where he could much more cleanly demonstrate localization, and this simplified problem is what later became known as "Anderson localization". Many-body localization at high temperature was then mostly neglected for the remainder of the 20th century. But now, developments in many-body atomic physics and in quantum information have inspired much recent work on many-body localization, most of which is theoretical, although experimental activity is now picking up speed. Many-body localization is a breakdown of equilibrium statistical mechanics because the many-body localized system does not go to thermal equilibrium under its own quantum dynamics: it fails to be able to serve as a thermal reservoir for itself. This breakdown occurs at a new type of quantum phase transition that is very different from previously known phase transitions. I will review some of our present understanding of this fascinating topic.

[recorded movie]


Apr. 5

Andrew Strominger

Harvard University

The Black Hole Information Paradox,  Revisited

Recent investigations have uncovered an infinite number of conserved quantities in essentially all theories with gravity or electromagnetism. We will give a review of these developments and their implications for the black hole information paradox. 

The talk will be in the Simons Center auditorium. Tea in the SCGP lobby at 3:45pm.

[recorded movie]


Apr. 12

Rosalba Perna 

Stony Brook University

Compact Objects from the death of massive stars: Probes of Fundamental Physics and Cosmological Tools

Massive stars, and the exotic compact objects they leave behind upon death, play a major role in shaping the evolution of the Universe. In addition, they provide an avenue for peeking into the early Universe, and probing aspects of fundamental physics. In this talk, I will focus on two special, albeit dramatic, subsets of phenomena associated with massive star deaths and their remnants:

gamma-ray bursts (GRBs) and magnetars, i.e. highly magnetized neutron

stars.  I will discuss how GRBs can be used to study the interstellar medium in very distant galaxies, and how their detection from the death of the first stars in the Universe can help set constraints on the small-scale power spectrum of density fluctuations, and hence on dark matter models. I will then present some ideas on using magnetars to probe axions, and I will conclude with a discussion of ongoing work on using gravitational waves from binary neutron star mergers to constrain the equation of state of dense matter.

[recorded movie]


Apr. 19

Stanley Brodsky


Novel Physics at the EI

A high energy electron-ion collider will bring exciting new perspectives to the study of hadron and nuclear physics, measuring the fundamental quark and gluon structure of hadrons and nuclei at the speed of light. I will discuss a number of novel effects predicted by quantum chromodynamics (QCD) which also can be tested at the EIC.  These include:

Tri-Jet Production -- Materializing the Proton's Light-Front Wavefunction.

Tests of Supersymmetric Relations between Meson and Baryons.

Studies of Shadowing and Flavor-Dependent Anti-Shadowing of Nuclear Structure Functions. Tests of the Validity of Fundamental Sum Rules for Nuclei.

Measurements of Intrinsic Heavy Charm and Bottom Quarks Distributions in the Proton at High Momentum. Probing the Physics of Diffractive Deep Inelastic Scattering. Measuring Charge Asymmetries due to Odderon-Pomeron and Z-Photon Interference. Single-Spin Asymmetries and the Breakdown of QCD Factorization Theorems. Creation of Exotic Hadrons: Tetraquarks, Pentaquarks, and Octoquarks. Tests of QCD Color Transparency. Tests of the Hidden-Color Properties of Nuclear Wavefunctions. Studies of the Ridge Phenomena and Novel Polarization Correlations in High Multiplicity Events at the EIC. Interference Effects from Virtual Photon and Z Exchange. Measurements of Virtual Photon-Photon and Virtual Z -Photon Collisions. Studies of Direct, Color-Transparent Hard Subprocesses and the Origin of the Baryon Anomaly.

I will also briefly discuss a new approach to quark confinement and the structure of hadrons from the fifth dimension which will also allow the study of hadronization at the amplitude level. This light-front AdS/QCD holographic approach gives a frame-independent, analytic,  first approximation for studying the  dynamics, spectroscopy, and excitation spectra of relativistic hadronic bound states in QCD which can be probed at the EIC.

[recorded movie]


Apr. 26

Anatoly Spitkovsky

Princeton University

Particle acceleration and magnetic field generation in astrophysical plasmas

Shocks in low density plasmas (so-called "collisionless shocks") are ubiquitous throughout the Universe, and are thought to be responsible for the generation of nonthermal particles that extend over decades in energy. I will describe the progress in modeling collisionless shock structure and particle acceleration using ab-initio kinetic simulations, focusing on the current understanding of magnetic field amplification mechanisms, the conditions necessary for particle injection into the acceleration process, and the physics behind the electron-to-ion ratio in cosmic rays.

[recorded movie]


May 3

graduate director

Graduate Awards Colloquium

[recorded movie]