High Energy Physics

For thousands of years, astronomy was restricted to what we could see with our eyes. But visible light makes up only a tiny fraction of a spectrum emitted by celestial objects.

We now know that light is not the universe’s sole means to reveal the mysteries of the heavens. Until recently, we simply lacked the windows through which to view these aspects of our universe.

Over the last few decades, astronomers have revolutionized our windows on the universe with telescopes of unprecedented sensitivity to light beyond what we can see with our eyes.

Observatories now allow us to see ghostly particles called neutrinos, and ripples in the fabric of space itself - called gravitational waves.

In his Perimeter Public Lecture on April 3, 2019, Chad Hanna will describe how these new windows have changed our view of the cosmos and explore what new wonders may be unveiled in the decades to come.

Hanna is an associate professor at Pennsylvania State University. His research focuses on studying the universe with gravitational waves using the Laser Interferometer Gravitational-Wave Observatory (LIGO).

Hanna and his research group work to enable multi-messenger astronomy through gravitational wave observations of merging neutron stars and black holes. Prior to joining Penn State, he was a senior postdoctoral researcher at Perimeter Institute.

I will give an overview of recent results on three-dimensional N=2 supersymmetric gauge theories placed on arbitrary half-BPS geometries. In particular, I will explain an explicit computation of the supersymmetric partition function on any Seifert three-manifold; such manifolds can have very intricate and interesting topology (for instance, a nice example is the Poincaré sphere) and can provide new interesting observables in 3d SCFTs. I will also discuss to which extent these results exhibit a generalisation of the 3d TQFT structure of Chern-Simons theory to non-topological (but supersymmetric) theories.
 

Bosonic ultra-light dark matter (ULDM) would form cored density distributions at the centres of galaxies. These cores admit analytic description as the lowest energy bound state solution ("soliton") of the Schrödinger-Poisson equations. Numerical simulations of ULDM galactic halos found empirical scaling relations between the mass of the large-scale host halo and the mass of the central soliton. 
We connect the simulation results of different groups to basic properties of the soliton. Importantly, simulations imply that the specific kinetic energy in the soliton and in the host halo should be approximately equal. This relation predicts that the peak circular velocity, measured for the host halo in the outskirts of the galaxy, should repeat itself in the central region. Contrasting this prediction to the measured rotation curves of low surface-brightness galaxies, we show that ULDM in the mass range m ~ 10⁻²²-10⁻²¹ eV, which has been invoked as a possible solution of small-scale puzzles of ΛCDM, is in tension with the data. We discuss the potential of detailed dynamical modelling of the Milky Way and other well-resolved galaxies to probe ULDM up to m ~ 10⁻¹⁹ eV.

Magnetohydrodynamics (MHD) describes the low-energy physics of electromagnetically conducting plasmas. In the conventional formulation of MHD, one introduces dynamical electromagnetic fields on top of the usual hydrodynamic setup by hand. In this talk, we will explore an alternate effective view of MHD purely based on symmetries, as a "string fluid" of magnetic field lines, without any assumption about the underlying microscopic field content. We will argue that MHD is described by a novel theory of superfluidity with a partially broken one-form symmetry. We will also discuss the implications of this broken symmetry for constructing hydrostatic partition functions describing MHD. The talk is based on [arXiv:1808.01939, arXiv:1811.04913].