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Monday, February 19th 2018

09:30 am:

12:15 pm:

In the coming decade we will witness the completion of CMB and 21 cm experiments that promise to lift the veil on reionization. Up until now, the details of reionization have remained shrouded in mystery across the chasm of space and time that separates us from the billion years after the big bang in which it occured, more than 12 billion years ago and 30 billion light years away due to cosmic expansion. CMB observations probe the distribution of what we think was a complicated network of growing and overlapping ionized bubbles created by UV and X-ray ancient dwarf galaxies and newborn supermassive black holes, while 21 cm observations probe the neutral patches left behind. As such, these two types of observations provide complementary information about the first billion years. I will discuss the exciting new prospects for understanding reionization by analyzing upcoming 21 cm and CMB observations jointly, emphasizing how simulations can help us avoid the pitfalls associated with teasing out the faint signals from nearby foregrounds, instrumental noise, and systematics.

3:30 pm:

I will provide an introductory level overview of recent

applications of resurgent trans-series and Picard-Lefschetz theory to

quantum mechanics and quantum field theory.

Resurgence connects local perturbative data with global topological

structures. In quantum mechanical systems, this program provides a

constructive relation between different saddles. For example, in

certain cases it has been shown that all information around the

instanton saddle is encoded in perturbation theory around the

perturbative saddle. In quantum field theory, such as sigma-models

compactified on a circle, neutral bions provide a semi-classical

interpretation of the elusive IR-renormalon, and fractional kink

instantons lead to the non-perturbatively induced mass gap exactly of

order of the strong scale. I also describe the concept of hidden

topological angle, a phase associated with Lefschetz thimbles.

Hidden topological angle may provide destructive/constructive

interference effects between equally dominant saddles in the Lefschetz

thimble decomposition, providing resolution to some time standing

puzzles in non-perturbative analysis.

Tuesday, February 20th 2018

12:20 pm:

The current generation of gravitational-wave (GW) detectors has already made phenomenal discoveries. One of the next frontiers of GW astrophysics is a measurement of the stochastic gravitational-wave background (SGWB). The SGWB is a superposition of many unresolvable stellar sources of GWs and potentially GWs from the earliest epochs of the Universe. Current searches for an SGWB rely on long cross-correlation measurements made with data from detectors separated by thousands of kilometers. The most likely source of correlated noise between detectors this far apart is extremely low frequency, persistent, electromagnetic waves like Schumann resonances. I'll discuss how these waves are produced, some recent measurements made using a global network of magnetometers, and how the waves can couple into GW detectors. Finally, I'll discuss development of methods to budget for and potentially subtract them from the GW data.

1:00 pm:

2:30 pm:

Microseconds after the Big Bang, the Universe cooled into an exotic phase of matter. There the fundamental building blocks of Quantum Chromodynamics (QCD), known as quarks and gluons, were not confined inside the core of atomic nuclei. Tiny specks of this early Universe matter, called the Quark-Gluon Plasma (QGP), are now being copiously produced in heavy ion collisions at both RHIC and the LHC. These experiments provide overwhelming evidence that the QGP flows like a nearly frictionless strongly coupled liquid over distance scales not much larger than the size of a proton. Thus, the QGP formed in particle colliders is the hottest, smallest, densest, most perfect liquid known to humanity. Yet, the theoretical underpinnings behind the liquid-like behavior of QCD matter remain elusive.

In this talk I will present first principles calculations performed within string theory and relativistic kinetic theory that have shed new light on the emergence of hydrodynamic behavior in QCD and challenged the very foundations of fluid dynamics. New techniques to determine the real time, far-from-equilibrium dynamics of QCD in the large baryon density regime will also be discussed to lead current experimental efforts to discover critical phenomena in the fundamental theory of strong interactions.

Wednesday, February 21st 2018

1:25 pm:

In normal metals, the electron's mean free path is much larger than its wavelength, allowing a semiclassical treatment of transport. Conversely, whenever scattering is so strong that the mean free path becomes comparable to the electron's wavelength, the concept of a quasiparticle becomes ill defined, and a new theoretical framework is needed. I will introduce a family of lattice models for interacting electrons that can be solved exactly in the limit of a large number of interacting electron flavors and/or phonon modes. Depending on details, these models exhibit either "resistivity saturation" at high temperatures to a value of the order of the quantum of resistance, or "bad metallic behavior" where the resistivity grows without bound with increasing temperature. Translationally invariant higher-dimensional generalizations of the Sachdev-Ye-Kitaev model can capture a variety of phenomena arising purely from electron-electron interactions, including local criticality, non-Fermi liquid, and marginal Fermi liquid behavior. I will describe the implications of these results for the problem of non-quasiparticle transport at large, local quantum criticality, and fundamental bounds on dissipation rates in quantum systems.

3:35 pm:

Thursday, February 22nd 2018

10:10 am:

12:05 pm:

3:35 pm:

Critical phenomena are one of the cornerstones of classical statistical mechanics. Quantum critical points (i.e., continuous phase transitions at zero temperature) in insulating materials are relatively well understood, by analogy with classical critical points in one spatial dimension higher. In contrast, the theory of quantum critical behavior in metals is still, to a large degree, open. Such metallic critical points are believed to play an important role in the physics of several "strongly correlated" materials, such as high temperature superconductors. Fortunately, many classes of metallic quantum critical points can be simulated efficiently using quantum Monte Carlo without the notorious "sign problem", which often hinders numerical simulations of fermionic systems. I will describe some recent progress along these lines, and how it sheds new light on some of the outstanding puzzles in the field.

Friday, February 23rd 2018

10:10 am:

12:20 pm:

Thermally activated hopping between energy minima in a double well system is expected to follow an Arrhenius Law. Experiments have shown that the rate of switching between two wells is proportional to the Boltzmann factor but little work has been done to probe the nature of the characteristic dwell time. A square, permalloy, mesoscale dot with an applied magnetic field can be used to create a double well system to explore the characteristic dwell time. I will show that the characteristic dwell time has an exponential dependence on the height of the barrier. There is a significant quantitative disagreement between accepted models of the dwell time and our results.

12:45 pm:

If the Peccei-Quinn symmetry breaking field is displaced from its minimum

during inflation, the axion isocurvature spectrum is generically strongly

blue tilted with a break transition to a flat spectrum. A test of this

scenario with the Planck and BOSS DR11 data will be presented. Encouraging

results and its implications for future probes of axions and inflationary

cosmology will be discussed.

2:30 pm:

The far-infrared (FIR) and (sub)millimeter bands provide us with unique views of structure formation in the Universe and the Galaxy alike. At these wavelengths we have the most adept probes of active star-formation that sample almost all of the reionized Universe (z~1--10) with essentially no bias. The Sunyayev Zel'dovich effect traces the assembly of galaxy clusters regardless of cosmological distance. Locally, in the Galaxy, FIR polarimetry probes the magnetic environments and dust properties around optically obscured young stars and cores, while FIR spectroscopy can spy on the ices in planetary disks. I will also highlight some of the ground-braking recent and upcoming instrumentation and technologies I work on to can deliver this scientific treasure trove.

3:35 pm:

It has long been maintained that Galenic/Hippocratic humoral theory reigned supreme in Islamic societies from when Greek medical texts were translated into Arabic in the ninth century till the arrival of European colonial powers in the nineteenth. Historians have provided various explanations for the persistence of humoral theory in Islamic societies ranging from the (alleged) religious prohibition against dissection to a predisposition amongst medical writers towards systematizing and summarizing rather than critical inquiry. Yet, medical writers engaged critically with medical theory in their commentaries on the Canon of Medicine and the Epitome. The leading figure in this critical engagement was Ibn al-Nafīs (d. 1288). Underlying his modification of humoral theory was a sustained critique of the Galenic physiological and anatomical understanding of digestion. Consequently, the paper provides evidence for Ibn al-Nafīs conducting anatomical observations on dead animals. Moreover, the fact that his new proposals were debated and accepted by later Islamic physicians counters the prevalent assumption that his works were ignored in the later period, and thus raises the distinct possibility that these new ideas on the humors and digestion were appropriated by Renaissance physicians such as Jean Fernel.

3:35 pm:

4:40 pm:

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