High Energy Physics

In this talk, I will detail two ways to search for low-mass axion dark matter using cosmic microwave background (CMB) polarization measurements. These appear, in particular, to be some of the most promising ways to directly detect fuzzy dark matter. Axion dark matter causes rotation of the polarization of light passing through it. This gives rise to two novel phenomena in the CMB. First, the late-time oscillations of the axion field today cause the CMB polarization to oscillate in phase across the entire sky. Second, the early-time oscillations of the axion field wash out the polarization produced at last-scattering, reducing the polarized fraction (TE and EE power spectra) compared to the standard prediction. Since the axion field is oscillating, the common (static) ‘cosmic birefringence’ search is not appropriate for axion dark matter. These two phenomena can be used to search for axion dark matter at the lighter end of the mass range, with a reach several orders of magnitude beyond current constraints. I will present a limit from the washout effect using existing Planck results, and discuss the significant future discovery potential for CMB detectors searching in particular for the oscillating effect.

[1903.02666]

The near horizon region of any black hole looks like flat space and displays an approximate Poincare symmetry. We study the way these symmetries are realized for near extremal black holes.

We construct SL(2) generators that move matter fields relative to the boundaries. The construction is exact to all orders in the gravitational coupling. We also display an approximate realization of these generators in terms of simple operators defined at the boundary. These can also be realized in the boundary quantum mechanical theory. We also discuss the realization of these in the SYK model.

Defects and their RG flows play an important role in many systems, with perhaps the most famous example being the Kondo effect. We study Kondo-like interface flows in D1/D5 holography from the point of view of both probe branes and of the corresponding backreacted supergravity solutions.

I will discuss the computation of second-order terms in the entanglement entropy and subregion complexity for a spherical entangling region in the AdS black hole background relative to pure AdS. I will suggest an extension of the conjectured relationship between subregion complexity and Fisher information into a relation that is reminiscent of the first law of thermodynamics. By analogy, entanglement and complexity play the roles of heat and work, respectively. Time permitting, I will also discuss the computation of third- and fourth-order terms in the relative entropy. 

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.