Light scalar fields arise naturally in beyond-the-standard-model scenarios in particle physics. They could contribute to the dark matter, the dark energy, or drive variation in the fundamental constants, such as the electric charge. I will review the imprint of (and resulting limits on) such models from the cosmic microwave background (CMB). I will then present new results on how to test these models using the high-redshift galaxy luminosity function and 21-cm radio emission during the cosmic dark ages, the era preceding star formation, beginning after CMB decoupling and continuing on to ~200 million years after the big bang.
Daniel Grin (Assoc. Prof, Dept of Physics & Astronomy, Haverford College) did his Ph.D. in astrophysics at Caltech, advised by Profs. Marc Kamionkowski and Chris Hirata. He then did postdoctoral fellowships at the Princeton Institute for Advanced Study and University of Chicago before coming to Haverford College. Dan works on a broad range of topics, including cosmic hydrogen recombination, axion dark matter (and dark energy), model-independent constraints to the dark sector, isocurvature fluctuations, variations in the fundamental constants, cosmic microwave background probes of new physics broadly, 21-cm cosmology, and more recently, the impact of dark matter physics on radio observations of galaxy and high-redshift luminosity function measurements.