University of Minnesota
School of Physics & Astronomy

Physics and Astronomy Calendar

Friday, February 17th 2017
Speaker: Masha Baryakhtar, Perimeter Institute
Subject: Searching for Ultralight Particles with Black Holes and Gravitational Waves

The LIGO detection of gravitational waves has opened a new window on
the universe. I 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, from axions to
dark photons. When a bosonic particle's Compton wavelength is
comparable to the horizon size of a black hole, superradiance of these
bosons into bound "Bohr levels" extracts energy and angular momentum
from the black hole. The occupation number of the levels grows
exponentially and the black hole spins down. One candidate for such an
ultralight boson is the QCD axion with decay constant above the GUT
scale. Current black hole spin measurements disfavor a factor of 30
(>100) in axion (vector) mass; future measurements can provide
evidence of a new boson. Particles transitioning between levels and
annihilating to gravitons may produce thousands of monochromatic
gravitational wave signals, and turn LIGO into a particle detector.

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