Prof. Yacine Ali-Haimoud, NYU

"Cosmological recombination as testing grounds for new physics"

Abstract: Cosmic Microwave Background (CMB) anisotropies are highly sensitive to cosmological recombination, the period during which the Universe transitioned from an ionized plasma to a mostly neutral gas. As a consequence, one can test a variety of non-standard physics through their imprint on recombination, hence, indirectly, on the CMB. In this talk I will highlight recent work on the topic in collaboration with Nanoom Lee and Trey Jensen. I will start by briefly reviewing the underlying standard recombination physics and numerical codes [in particular 2007.14114]. I will then discuss what it would take to solve the Hubble tension from small modifications to cosmological recombination [2212.04494]. Lastly, I will present a new observational test of accreting primordial black holes, based on the CMB trispectrum sourced by their inhomogeneous effect on recombination [2106.10266 and 2212.00075].

My brief bio: I graduated in 2011 from Caltech, where I did my PhD with professor Chris Hirata I then went to the Institute for Advanced Study for a postdoc from 2011 to 2014, and to Johns Hopkins University, in Marc Kamionkowski's group, for a second postdoc from 2014 to 2017. I have been faculty at NYU since 2017. I am interested in a broad range of topics in theoretical cosmology and astrophysics, including dark matter, the cosmic microwave background, interstellar dust, and modified gravity.