Talks

We will discuss how the process of superradiance, combined with
gravitational wave measurements, makes black holes into
nature's laboratories to search for new light bosons. We will present
analytic results for superradiance of light vector (spin-1) particles,
valid in the regime where the vector's Compton wavelength is much
larger than the horizon size of a black hole. If superradiance is
efficient, the occupation number of the vectors in the black hole's
vicinity grows exponentially and the black hole spins down. We will
present preliminary signatures of this process, including black hole
spin measurements and gravitational wave signals. Current measurements
of black hole spins disfavor a range of masses of (gravitationally
coupled) vectors. Vectors annihilating to gravitons would emit
strong monochromatic gravitational wave signals, which may be
visible in future LIGO observations. 

The discovery of the Higgs boson at the LHC in 2012 was a watershed in particle physics. Its existence focuses attention on the outstanding questions about physics beyond the Standard Model: is `empty' space unstable? what is the dark matter? what is the origin of matter? what is the explanation for the small masses of the neutrinos? how is the hierarchy of mass scales in physics established and stabilized? what drove inflation? how to quantize gravity Many of these issues will be addressed by future runs of the LHC, e.g., by studies of the Higgs boson, and also motivate possible future colliders.

Dicke's seminal 1954 paper introduced the notion of `superradiance' in a system of spins coupled to a common photon mode.

Certain quantum states of the spins dominate the radiation process so that the spins radiate coherently. Dicke's original thought experiment has recently been recreated in the lab using cavity-QED setups with two spins. I will explore extending this experiment to $N$ spins and show that the radiation process naturally gives rise to entangled states. This suggests a new experimental tool to create multi-particle entanglement in the lab. In particular, a null-observation (non-observation of emitted photon) can be used to collapse the wavefunction onto a dark state. Remarkably, this dark state has resonating valence bond character. We show that the probability of collapse onto RVB state scales as $N^{-1}$, making it possible to generate entangled states of more than 20 spins.

Reference: arXiv:1609.04853

In the first part of the talk, I will explain how the lengths of non-minimal geodesics in AdS3 conical defect backgrounds can be interpreted as the entanglement entropy of certain subalgebras in the dual CFT. This part will be based on 1608.02040. In the second part of the talk, I will discuss how the Ryu-Takayanagi area term seems to be the analog of a certain edge term for EE in a gauge theory, and how one might try to test this. This part is more speculative.

A very close supernova explosion could have caused a mass extinction

of life in Earth. In 1996, Brian Fields, the late Dave Schramm and the
speaker proposed looking for unstable isotopes such as Iron 60 that could
have been deposited by a recent nearby supernova explosion. A group from
the Technical University of Munich has discovered Iron 60 in deep-ocean
sediments and ferromanganese crusts due to one or more supernovae that
exploded O(100) parsecs away about 2.5 million years ago. These results
have recently been confirmed by a group from the Australian National
University, and the Munich group has also discovered supernova Iron 60 in
lunar rock samples and in microfossils of magnetotactic bacteria. 
This colloquium will discuss the data and their interpretation
in terms of supernova models, and the possible implications for
life on Earth.