Scientific Series

Almost fifteen years after LIGO started listening to the cosmos, and 100 years after Einstein discovered general relativity, gravitational waves have been detected by ground-based interferometers, opening a new window on the universe. In this talk I will address some of the most exciting areas of research advanced LIGO will allow us to explore in the coming years. Detection and characterization of gravitational wave transients will be discussed, as well as their impact on astrophysics.

I will discuss the recent LHC excess in the di-photon distribution at an invariant mass of 750 GeV.  Various explanations in terms of weakly coupled and strongly coupled physics will be presented. Possible connection with Dark Matter will also be discussed.

In recent decades probing for the subtle indications of new physics in
experimental data has become increasingly difficult. The datasets have gotten
much bigger, the experiments more complex, and the signals ever smaller. Success
stories, like LIGO and Kepler, require a sophisticated combination of statistics
and computation, coupled with an appreciation of both the experimental realities
and the theoretical framework governing the data.

In this talk I will look broadly at data science in physics, and how and why it
has taken an increasingly central role. I'll highlight specifically my current
area of research, radio cosmology: discussing why it is one of the most
challenging areas for data science, and describing my work developing optimal
and efficient statistical methods for turning terabytes of timestreams into
cosmology.

In this talk, I will investigate the structure of certain protected operator algebras that arise in threedimensional N = 4 superconformal field theories. I will show that these algebras can be understood as a quantization of (either of) the half-BPS chiral ring(s). An important feature of this quantization is that it has a preferred basis in which the structure constants of the quantum algebra are equal to the OPE coefficients of the underlying superconformal theory. I will present evidence in examples that for a given choice of quantum algebra (defined up to a certain gauge equivalence), there is at most one choice of canonical basis, and conjecture that this is true in general.

Our physical theories often admit multiple formulations or variants.  Although these variants are generally empirically indistinguishable, they nonetheless appear to represent the world as having different structures.   In this talk, I will discuss several criteria for comparing empirically equivalent theories that may be used to identify (1) when one variant has more structure than another (i.e., when a formulation of a theory has “excess structure”) and (2) when two variants are theoretically equivalent, even though they appear to represent the world differently.  I will then discuss where this leaves the philosopher trying to use our empirically successful theories as a guide to the structure of the world.

I will discuss the cosmology of galileon models with a Minkowski limit and discuss whether they can account for the currently observed cosmological model. The full galileon model predicts the speed of gravitational waves to be different from that of photons. I will discuss this and compare with observations. I will then discuss a subdominant galileon model which is compatible. Finally I will discuss the shape dependence of screening in galileon models, showing that the fifth force is unscreened for planar objects.

I will begin by giving an overview of the current state of exoplanet
science, a field that has advanced tremendously in just the last few
years.  While specialized instrumentation and observational facilities
have provided the data driving this advance, the development and
application of statistical techniques to interpret this data have been
of critical importance.  These same tools are also at the core of all
data-driven science, and are thus applicable to many other fields of
astrophysics that will be acquiring increasingly large and rich
datasets in the coming years.  I will highlight a few examples of
particular interest to fundamental physics, including gravitational
wave observations, fast radio bursts, and cosmological surveys.

Understanding the microscopic nature of dark matter (DM) is one of the most outstanding problems facing modern physics.  There is to-date no evidence for non-gravitational interactions of DM with the rest of the Standard Model and also no hint for any particular DM mass.  My talk with focus on new techniques to search for GeV-TeV scale weakly-interacting DM by looking for DM annihilating in the cosmos into cosmic rays such as gamma-rays and neutrinos. These potential signs of new physics are easily confused with standard but poorly understood astrophysical backgrounds, such as populations of dim point sources (PSs) like millisecond pulsars.  I will present new methods to characterize Galactic and extra-Galactic PS populations, which have complicated DM searches in these regions.  I will show that accounting for unresolved PSs in Fermi gamma ray data leads both to new constraints on the dark sector along with some unexpected surprises.  I will conclude by briefly describing a new idea for a laboratory experiment able to probe ultra-light axion DM, with masses some 20 orders of magnitude smaller than the weak scale.

The fact that the Einstein-Hilbert action, by itself, does not lead to a well-posed variational principle has become textbook knowledge. It can be made well-posed by the addition of suitable boundary terms. There are many boundary terms available in the literature, of which the most famous and most widely used is the Gibbons-Hawking-York (GHY) boundary term. The GHY term is ostensibly defined only for a non-null boundary. There have been very few efforts in the literature to extend its definition to null boundaries. The speaker will present his group's work towards finding a boundary term to render the Einstein-Hilbert action well-posed in the presence of null boundaries. He shall discuss a proposed boundary term, associated boundary conditions, outstanding issues and possible applications.