Physics

Most of the matter in the Universe is dark; determining the composition and interactions of this dark matter is among the defining challenges in particle physics today. I will briefly summarize the present status of dark matter searches and the case for exploration beyond the WIMP paradigm, particularly “light dark matter” close to but beneath the weak scale. I will define sharp milestones in sensitivity needed to decisively explore the best-motivated light dark matter scenarios, and describe experimental techniques to reach these milestones over the next several years.

The spatially-indirect exciton condensates (SIXC) is an interesting ordered electronic state in which coherence is spontaneously established between particles localized in separate two-dimensional layers. I will discuss some of the properties SIXCs, commenting on their counterflow superfluidity, their collective excitations, and on similarities and differences relative to superconductors, easy-plane ferromagnets and anti-ferromagnets, and the standard model of particle physics.  Finally I will discuss the prospects of achieving SIXC states at elevated temperatures in multi-layer 2D material systems.   

In the last few years there has been significant interest in the possible applications of gauge-gravity duality to condensed matter systems. In this talk I will discuss recent applications of these holographic techniques to strongly correlated systems out of equilibrium. I will argue that insights from general relativity, hydrodynamics and quantum field theory may be combined to yield quantitative predictions for quantum transport.

Over Twenty-five years into the internet era, over twenty years into the WorldWideWeb era, fifteen years into the Google era, and a few years past the Facebook/Twitter era, we've yet to converge on a new long-term methodology for scholarly research communication. I will provide a sociological overview of our current metastable state, and then a technical discussion of the practical implications of literature and usage data considered as computable objects, using arXiv as exemplar. From the physics standpoint, there is a surprising amount of statistical mechanics in text-mining and machine learning.

There is an analogy between the propagation of fields in the vicinity of astrophysical black holes and the that of small excitations in fluids and superfluids. This analogy allows one to test, challenge and verify, in tabletop experiments, the elusive processes of black hole mass and angular momentum loss.

I will first present a brief overview on analogue black hole experiments, and then discuss in more detail some of my earlier and more recent experimental and theoretical results on the subject.

Galileons are higher-derivative effective field theories with curious properties which have attracted much recent interest among cosmologists.  I will review their origins, their properties, their generalizations, and some recent developments.

Calculations in General Relativity inevitably involve tricky manipulations of tensor equations. In many cases, the tensor algebra involved is at best tedious and fraught with error, and at worst impossible. It is, however, ideally suited to implementation in a computer algebra system such as Mathematica. In this talk I will show how the xAct tensor algebra package can be used to make light work of difficult tensor calculations. I will illustrate its wide-reaching functionality using applications in my own research, with relevance to black hole perturbations, numerical relativity and quantum gravity.

In holographic duality a gravitational spacetime emerges as an equivalent description of a lower-dimensional conformal field theory (CFT) living on the asymptotic boundary. Traditionally, the dimension not present in the CFT is interpreted in terms of its Renormalisation Group flow. In this talk I exploit the relation between boundary entanglement entropies and bulk minimal surfaces to define a quantitative framework for the holographic Renormalisation Group, in which quantum information theory plays a fundamental role. I will provide operational, quantitative, information-theoretic characterizations of several geometric concepts in asymptotically AdS3 spacetimes, including the radial direction and lengths of bulk curves.

Perhaps the biggest conceptual benefit of the information-theoretic framework for holographic Renormalisation Group is a quantitative correspondence between holography and the Multi-Scale Entanglement Renormalisation Ansatz (MERA). I also discuss prospects for understanding the near-horizon structure of black holes.

After 50 years of dreaming about it, space-based microlensing observations are now underway.  A 2014 100-hr Spitzer Pilot Program generated "microlens parallaxes" for dozens of lenses, opening the prospect of measuring the Galactic distribution of planets.  This program will be expanded 8-fold in 2015.  Analogous observations by Kepler will measure the mass function of free-floating planets.

WFIRST microlensing observations will, as advertised, "complete the planetary census" but they will do an immense amount of astrophysics as well.  I discuss how microlensing's take off builds on rapid, ongoing, ground-based developments.

Water Stress:
Seeking Solutions in the
Unusual Properties of Water

Water is ubiquitous, but the availability of fresh water is limited. Today, one in six people is under “water stress,” meaning that they have no access to clean water. It is one of the many paradoxes of water. This essential liquid, which in many ways is so commonplace, is also very peculiar. Water behaves differently than other materials in more than 70 ways. These anomalies not only keep our bodies in balance, but secure the thermal stability of our planet as well. Whereas most liquids contract when cooled, water does the opposite – it expands as temperature drops, which, among other effects, allows fish to survive the winter. What’s more, water diffuses more quickly as a system becomes denser – the opposite behaviour to most other fluids.

In her Perimeter Institute Public Lecture, physicist Dr. Marcia C. Barbosa will examine how we can better understand this precious resource that is both incredibly abundant on Earth, yet dangerously scarce to millions of people. Decoding the strange properties of water, Barbosa argues, may be essential to resolving the widespread problem of water stress.

We investigate through non-equilibrium molecular dynamic simulations the flow of anomalous
fluids inside rigid nanotubes. Our results reveal an anomalous increase of the overall mass flux
for nanotubes with sufficiently smaller radii. This is explained in terms of a transition from a
single-file type of flow to the movement of an ordered-like fluid as the nanotube radius increases.
The occurrence of a global minimum in the mass flux at this transition reflects the competition
between the two characteristic length scales of the core-softened potential. Moreover, by increasing
further the radius, another substantial change in the flow behavior, which becomes more evident at
low temperatures, leads to a local minimum in the overall mass flux. Microscopically, this second
transition is originated by the formation of a double-layer of flowing particles in the confined
nanotube space. These nano-fluidic features give insights about the behavior of confined isotropic
anomalous fluids.

The remnant accretion disk formed in binaries involving neutron stars and/or black holes is a source of non-relativistic ejecta. This 'disk wind' is launched on a thermal and/or viscous timescale, and can provide an amount of material comparable to that in the dynamical ejecta. I will present recent work aimed at characterizing

the properties of these winds through time-dependent radiation-hydrodynamic simulations that include the relevant physics needed to follow the ejecta composition. I will focus on the effect of black hole spin and/or hypermassive neutron star lifetime on the disk wind, and on the interaction of the wind with the dynamical ejecta. I will also discuss the implications of these results for the optical/IR signal from these events, and for the origin of r-process elements in the Galaxy.