Cosmology

Albert Einstein predicted a century ago the existence of gravitational waves – ripples in the fabric of spacetime moving at the speed of light. It was believed that these ripples were so faint that no experiment would ever be precise enough to detect them. But in September 2015, LIGO did exactly that. The teams working with the Laser Interferometer Gravitational-wave Observatory (LIGO) detectors in Louisiana and Washington measured a loud gravitational wave signal as it traveled through the Earth after a billion-year journey from the violent merger of two black holes.

Since that first detection, scientists have measured many more gravitational waves, including a signal produced by colliding neutron stars captured by LIGO and the Virgo detector in Europe in 2017. That cataclysm also generated electromagnetic waves – light – detected by numerous other telescopes, and helped scientists understand how gold is created in deep space.

In a special public lecture webcast at Perimeter Institute on October 23, 2019, Gabriela González will provide a first-hand account of LIGO’s century-in-the-making breakthrough, and explain observations made as recently as this year. González, a professor of physics and astronomy at Louisiana State University and former spokesperson of the LIGO collaboration, will take the audience on a journey to some of the universe’s most violent places, and explain how such distant events can lead to a very bright future here on Earth.

A massive U(1)' gauge boson known as a “dark photon” or A', has long been proposed as a potential explanation for the muon g − 2 anomaly. Recently, experimental results have excluded this possibility for a dark photon decaying visibly and invisibly. I revisit this idea and consider a model where A' couples to inelastic dark matter, leading to a semi-visible decay mode. I show that for large mass splittings between the dark sector states this decay mode is enhanced, weakening the invisibly decaying dark photon bounds. As a consequence, A' resolves the g −2 anomaly in a region of parameter space the thermal dark matter component of the Universe is readily explained.

Large galaxy surveys have dramatically improved our understanding of astrophysics and cosmology in the high-redshift universe, but they are fundamentally limited by the need to integrate long enough to detect each individual source. Line intensity mapping has recently arisen as a powerful alternative to these surveys, offering access to fainter sources and larger volumes than conventional techniques. There has been a surge of experimental interest in this technique, with surveys planned or in progress across the electromagnetic spectrum. In this talk, I will describe the wide variety of science which we will obtain from these experiments in the next few years and illustrate the methods by which we can go from maps of confused line emission to useful astrophysics. I will show how intensity maps can give new insights into topics ranging from star formation to the high-redshift ISM to the Hubble constant tension. I will further discuss the utility of combining intensity maps with conventional surveys, both for systematics control and for studying processes like AGN feedback. I will close with a discussion of how modern machine learning methods can be used to further extend what we can learn from these surveys.